Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013 Article ID 157494 9 pageshttpdxdoiorg1011552013157494
Research ArticleThe Microstructure and Capacitance Characterizations ofAnodic Titanium Based Alloy Oxide Nanotube
Po Chun Chen1 Sheng Jen Hsieh2 Chien Chon Chen3 and Jun Zou1
1 Department of Electrical Engineering Texas AampM University College Station TX 77843-3128 USA2Department of Engineering Technology Texas AampM University College Station TX 77843-3367 USA3Department of Energy Engineering National United University Miaoli 36003 Taiwan
Correspondence should be addressed to Chien Chon Chen chentexasgmailcom and Jun Zou junzouecetamuedu
Received 15 April 2013 Accepted 18 June 2013
Academic Editor Anukorn Phuruangrat
Copyright copy 2013 Po Chun Chen et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
This paper presents a simple anodization process to fabricate ordered nanotubes (NTs) of titanium and its alloys (Ti-Mo and Ti-Ta)TiO2 MoO
3 and Ta
2O5are high dielectric constant materials for ultracapacitor application The anodic titanium oxide contains a
compact layer on the NT film and a barrier layer under the NT film However the microstructure of oxide films formed by anodicTi-Mo and Ti-Ta alloys contains six layers including a continuous compact layer a continuous partial porous layer a porous layera net layer an ordering NT film and an ordering compact barrier layer There are extra layers which are a partial porous layer anda porous layer not presented on the TiO
2NT film In this paper we fabricated very high surface area ordered nanotubes from Ti
and its alloys Based on the differences of alloys elements and compositions we investigated and calculated the specific capacitanceof these alloys oxide nanotubes
1 Introduction
The demands for energy storage and energy generation areincreasing rapidly with the global energy crisis Ultracapac-itor is a technology for energy storage with advantages oflow cost and high efficiency Barium titanate (BaTiO
3) which
exhibits a very high dielectric constant is a good materialfor ultracapacitor fabrication [1ndash4] However the processesof producing BaTiO
3 such as hydrothermal treatment [5
6] metal-organic process [7] alkoxide hydrolysis [8 9] RFsputtering [10] and sol-gel process [11] have been reportedand they are very complex and costly Titanium dioxide(TiO2) can be formed nanotube by one-step anodizing
process compared with the complex processes fabricatingBaTiO
3 However the dielectric constant of TiO
2is not
as high as BaTiO3 but TiO
2nanotube could be an ideal
dielectric template due to its high surface area A typical TiO2
nanotube fabrication can be achieved by anodization[12]and the ordered channel array of anodic titanium oxidenanotubes is able to serve as multiple parallel dielectric layersfor the ultracapacitor
On the other hand metals (Al [13] Hf [14] Nb [15]Ta [16] W [17] and V [18]) and alloys (Ti-Mo [19] Ti-W[20] Ti-Nb [21] Ti-V [22] Ti-Zr [23] Ti-Ta [24] and Ti-Al [25]) have been reported that they can also be formedhigh surface area of nanoporous oxide filmWO
3 Ta2O5 and
TaTiO3 which have higher dielectric constants than TiO
2 of
1000 [26] 110 [27] and 200 [28] are the alternate dielectricmaterials for ultracapacitor Unfortunately they cannot formnanotubes structures as good as TiO
2nanotubesThus in this
paper we used a simple process of anodization to fabricateTiO2 TiO2-MoO
3 and TiO
2-Ta2O5nanotubes Their high
dielectric constants and large surface areas are very usefulmaterials to build ultracapacitors Based on the nanotubestructural properties such as diameter porosity and lengthwe also investigated the specific capacitances of the differenttitanium alloys
2 Experimental Procedure
An ordered channel array of anodic titanium and titaniumalloy oxides was fabricated by anodizing Ti Ti-10Ta (90wt
2 Journal of Nanomaterials
135120583m
(a)
135120583m
(b)
05 120583m
(c)
135120583m
(d)
05 120583m
(e)
05 120583m
(f)
Figure 1 SEM images of TiO2NT (a) an unwanted film cover onTiO
2NT (b) partial unwanted film removed (c) all unwanted films removed
and TiO2NT presented (d) TiO
2NT side view (e) TiO
2NT bottom view and (f) a barrier layer on the TiO
2NT bottom
Ti + 10wt Ta) Ti-20Ta (80wt Ti + 20wt Ta) andTi-10Mo (90wt Ti + 10wt Mo) alloys The metal sub-strates were first put through electropolishing (EP) The EPelectrolyte included 5 volperchloric acid (HClO
4) 53 vol
ethylene glycol monobutylether (HOCH2CH2OC4H9) and
42 vol methanol (CH3OH) EP processes of Ti and Ti
alloys were conducted at 15∘C under 52V for 1 minute and28V for 13 minutes with platinum as a counter electrodeat a constant stirring rate of 200 rpm After EP the sampleswere etched in 5 vol HF for 5min to form an additionalthin anodic film on the metal substrates TiO
2 TiO2-Ta2O5
and TiO2-MoO
3nanotubes were anodized in an electrolyte
of 05 wt ammonium fluoride (NH4F 999) and 2wt
H2O in ethylene glycol (C
2H4(OH)2) solvent at a constant
voltage of 60V for 2 hours After anodic films were formedby anodization the films were then annealed in an airfurnace at 450∘C for 1 hour for crystallization The surfacemorphologies of the anodic oxides were observed by usinga scanning electron microscope (SEM FEI Quanta 600)The alloy oxide nanotubes compositions can be analyzed byEnergy Dispersive Spectrometer (EDS) (Oxford)
Cyclic voltammetry (CV) performances were evaluatedby an electrochemical analyzer (CH Instruments Model600B USA) using a standard three-electrode cell systemwithplatinum as a counter electrode and silver-silver chlorideelectrode (AgAgCl) as a reference electrode in 05M H
2SO4
solution at room temperature The CV scan rate was set as20mVs in a potential range of 0V to 09V (AgAgCl)
Journal of Nanomaterials 3
16
06
2 146 10Ti
pH
TiO
minus2
minus04
minus14
minus24
TiO3+3
TiO2+
Ti3+
Ti2+ Ti(OH)3
HTiOminus3
HTiOminus4
Ti(OH)4
E(V
)
TiO3middot2H2O
(a)
pH
0
1
2
0 4 8 12
Ta
TaO+2 Ta2O5
E(V
)
minus1
minus2
(b)
pH
02
07
12
0 3 6 9 12
Mo
H2MoO4
MoO3
MoO2minus4
MoO2
E(V
)
minus08
minus03 Mo3+
(c)
Figure 2 Pourbaix diagrams of (a) Ti (b) Ta and (c) Mo
3 Results and Discussion
Figure 1 presents the SEM images of long-range orderednanochannel TiO
2NT structures formed by anodizing pure
Ti foil (a) an unwanted film covered on TiO2NT (b) partial
unwanted film removed (c) all unwanted films removed andthe top view of TiO
2NT (d) side view of TiO
2NT (e) bottom
view of TiO2NT and (f) a barrier layer under the TiO
2NT
TiO2NT feature a pore diameter sim120 nm pore density sim8
times 109 porescm2 and wall thickness sim25 nm the length ofthe NT can be controlled from several 120583ms to hundred 120583mswith different types of the electrolytes (eg NH
4F) and the
anodization times at a constant applied voltage (eg 60V)Immersing titanium in electrolyte causes complex reac-
tions with 16 forms of Ti ions and oxides [29] The Pourbaixdiagram is useful to simplify the complex reactions [30]Based on the Pourbaix diagram of Ti (Figure 2(a)) TiO2+ion is a favorite formation when pH value is lower than 23and voltage is higher than minus02 V (SHE) at 25∘C TiO2+ canfurther react with H
2O to from Ti(OH)
4which is anodic
titanium oxide Similarly Ta Pourbaix diagram (Figure 2(b))shows that TiO2+ is formed and converted to Ta
2O5under the
condition of pH lt 51 and applying voltage gtminus12 V (SHE) atroom temperature Also Mo Pourbaix diagram (Figure 2(c))implies that Mo3+ can be produced and form MoO
3in the
condition of pH being below 42 and voltage being higherthan minus035V (SHE) at 25∘C However anodic TiO
2 MoO
3
and Ta2O5can be formed in the neutral pH value electrolyte
when it contains halogen element in it
Anodization of titanium forms close-packed and vertical-aligned nanotubes in a nonaqueous organic polar electrolytewith Fminus ions and minimizing water content These electro-chemical processes can be described as follows [31ndash34]
Ti 997888rarr Ti4+ + 4eminus (1)
H2O 997888rarr 2H++O2minus (2)
Ti4+ + 2O2minus997888rarr TiO2 (3)
Ti4+ + 2H2O 997888rarr 4H++ TiO2 (4)
6Fminus + TiO2 + 4H+997888rarr [TiF6]
2minus+ 2H2O (5)
[TiF6]2minus+ 119899H2O 997888rarr [TiF6minus119899(OH)
119899]2minus + 119899H+
+ 119899Fminus (6)
[TiF6minus119899(OH)119899]
2minus+ (6 minus 119899)H2O
997888rarr [Ti(OH)6]
2minus+ (6 minus 119899)H+ + (6 minus 119899) Fminus
(7)
[Ti(OH)6]
2minus+ 2H+ 997888rarr TiO
2+ 4H2O (8)
During anodization there are oxidation reactions at theinterface between metal and electrolyte Ti4+ is formed andthe water in the electrolyte is decomposed reactions (1) and(2) TiO
2is then formed between themetal and the electrolyte
through ion migration reactions (3) and (4) Fminus ions etch theTiO2forming [TiF
6]2minus and then combine with the H
2O to
form [TiF6minus119899(OH)119899]
2minus reactions (5) and (6) Because the Fminusions are doped in the TiO
2but do not form a compound
reaction (6) can be rewritten as (7) Finally [Ti(OH)6]
2minus
reacts with 2H+ to form TiO2nanotubes reaction (8)
4 Journal of Nanomaterials
10120583m
(a)
1120583m
(b)
125 120583m
(c)
125 120583m
(d)
05 120583m
(e)
Figure 3 SEM images of Ti-Ta NT film structure (a) compact layer (b) partial porous film (c) porous film (d) net film and (e) Ti-Ta NT
Based on reactions (1)ndash(8) anodization of Ta can bedescribed as
Ta 997888rarr Ta5+ + 5eminus (9)
H2O 997888rarr 2H++O2minus (10)
2Ta5+ + 5O2minus 997888rarr Ta2O5 (11)
2Ta5+ + 5H2O 997888rarr 10H+ + Ta
2O5
(12)
12Fminus + 2Ta2O5+ 10H+ 997888rarr 2[TaF
6]
minus+ 5H2O (13)
2[TaF6]
minus+ 2119899H
2O 997888rarr 2[TaF
6minus2119899(OH)2119899]
minus+ 2119899H+ + 2119899Fminus
(14)
2[TaF6minus2119899(OH)2119899]
minus+ (6 minus 2119899)H2O
997888rarr [Ta(OH)6]
minus+ (6 minus 2119899)H+ + (6 minus 2119899) Fminus
(15)
2[Ta(OH)6]
minus+ 2H+ 997888rarr Ta
2O5+ 7H2O (16)
Journal of Nanomaterials 5
1120583m
(a)
1120583m
(b)
1120583m
(c)
1120583m
(d)
Figure 4 SEM images of TiO2-Ta2O5nanotubes film by anodizing Ti-20Ta alloy (a) a net film on the NT top (b) without a net film on the
NT top (c) a barrier layer on the NT bottom and (d) partial barrier layer on the NT bottom
Also anodization of Mo can be described as
Mo 997888rarr Mo3+ + 3eminus (17)
H2O 997888rarr 2H++O2minus (18)
Mo3+ + 3O2minus 997888rarr MoO3
(19)
Mo3+ + 3H2O 997888rarr 6H++MoO
3(20)
6Fminus +MoO3+ 6H+ 997888rarr [MoF
6]
3minus+ 3H2O (21)
[MoF6]
3minus+ 119899H2O 997888rarr [MoF
6minus119899(OH)119899]
3minus+ 119899H+ + 119899Fminus
(22)
[MoF6minus119899(OH)119899]
3minus+ (6 minus 119899)H2O
997888rarr [Mo(OH)6]
3minus+ (6 minus 119899)H+ + (6 minus 119899) Fminus
(23)
[Mo(OH)6]
3minus+ 3H+ 997888rarr MoO
3+ 3H2O (24)
Figure 3 shows SEM images of TiO2-Ta2O5nanotubes
structure from anodizing Ti-10Ta alloy There was a compactlayer on the top of nanotubes in Figure 3(a) A continuousporous layer and grain boundary under the compact layer
are observed in Figure 3(b) Figure 3(c) shows a porous filmis covering the compact layer and following a net structure(Figure 3(d)) is covering the gap between ordered TiO
2-
Ta2O5nanotubes (Figure 3(e)) There were extra continuous
porous layers and net structures which were not presented onpure TiO
2nanotubes The compact layer continuous porous
layer andnet structurewere removed by 5wtof 1120583mAl2O3
powders in ethanol solvent assisted by ultrasonic vibrationSimilar to Ti-10Ta alloy Figure 4 shows SEM images ofTiO2-Ta2O5nanotube by anodizingTi-20Ta alloy Figure 4(a)
shows a net film on the NT top Figure 4(b) without a net filmon the NT top Figure 4(c) a barrier layer on the NT bottomand Figure 4(d) partial barrier layer under the NT
For the Ti-10Mo alloy Figure 5(a) shows partially re-moved continuous porous layer on the net structure largerpores on the top of TiO
2-MoO
3nanotubes (Figure 5(b))
smaller pores (Figure 5(c)) and barrier layer (Figure 5(d))on the bottom side According to Figures 3ndash5 Figure 6 is aschematic diagram of anodic Ti alloy oxide structure withcompact layer continuous porous layer net structure andordered nanotubes on the alloys surfaces
Figure 7 shows a schematic structure and geometry ofthe Ti alloy oxide nanotube Larger open pores are on the
6 Journal of Nanomaterials
125 120583m
(a)
05 120583m
(b)
1120583m
(c)
125 120583m
(d)
Figure 5 SEM images of TiO2-MoO
3nanotubes film by anodizing Ti-10Mo alloy (a) a porous film and a net film on theNT top (b) a cleaned
NT top (c) small pores on the NT bottom and (d) a barrier layer on the NT bottom
Table 1 EDS results of Ti alloys oxide nanotubes
TiO2 () Ta2O5 () MoO3 ()Ti-20Ta 839 161 0Ti-10Ta 913 87 0Ti-10Mo 928 0 72
top (Figure 7(a)) smaller closed pores and a barrier layerin a hexagonal pattern are on the bottom side (Figure 7(b))tube inner surface area (Figure 7(c)) and outer surfacearea (Figure 7(d)) Denoting 119877
1and 119877
2 and 119879
1and 119879
2are
the radius and pores width of the top and bottom poresrespective119882 is the thickness of the outer barrier layer and119867 and 119871 is the inner height and total length of the nanotubeWe have 119877
1+ 1198791= 1198772+ 1198792= 1198773 and total length of nanotube
is 119871 = 119867+119882 Thus the volume of a single alloy oxide can becalculated by119881 = 119881outer minus119881inner where119881outer and119881inner can beobtained by
119881outer = 1205871198772
3times 119871
119881inner =1
3
120587 times
119867
119877
1minus 119877
2
times (119877
3
1minus 119877
3
2)
(25)
Based on the SEM images in Figures 3 4 and 5119877111987721198773
and 119882 were 60 nm 25 nm 80 nm and 40 nm respectivelyFor two hours anodization process 20120583m length of Ti alloyoxide nanotubes (119871) could be formed on the Ti alloy surfaceThus 119881outer was 04120583m
3 and 119881inner was 012 120583m3 and the
volume of a single alloy oxide nanotube (119881) was 028120583m3The TiO
2nanotubes density has been recently reported by
Chen et al [29] such that there are 4510548978 nanotubesper cm2 Therefore the total volume of Ti alloy nanotubeswas 126 times 10minus3 cm3 in 1 cm2 sample area Moreover it hasalso been reported that nanotube surface area is greatlyincreased when 119871 = 10 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 and 119871 = 100 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 Figure 8 furthermore accumulated anodic Ti andTi alloy NT inner and outer surface areas increased withfilm thickness increased based on 1 cm2 substrate Hence theextremely high surface area is able to provide more chancesfor electrochemical reactions
According to the Pourbaix diagrams in Figure 2 anodiz-ing Ti Ti-20Ta Ti-10Ta and Ti-10Mo can form anodic oxidefilms of these Ti alloys Therefore the following alloy anodicoxide films densities are able to be calculated based on theTiO2 Ta2O5 andMoO
3densities of 42 gcm3 82 gcm3 and
Journal of Nanomaterials 7
Table 2 Specific capacitance based on TiO2 NT Ti-10Ta NT Ti-20Ta NT and Ti-10Mo NT films
Sample size (1 cm2times 20 120583m) TiO2 NT Ti-10Ta NT Ti-20Ta NT Ti-10Mo NT
Density (gcm2) 309 319 365 307Mass of unit area (mgcm2) 618 638 730 614119889119876 (mC) 6558 12002 14330 10292119889119864 (V) 09 09 09 09Specific capacitance (Fg) 118 209 218 186
(a)
(b)
(c)
(d)
Ti-Ta or Ti-Mo alloy
Barrier layer
TiO2-Ta2O5NT or TiO2-MoO3 NT
(e)
Figure 6The schematic diagram of TiO2-Ta2O5NT or TiO
2-MoO
3
NT film structure (a) compact layer (b) partial porous film (c)porous film (d) net film and (e) TiO
2-Ta2O5NT or TiO
2-MoO
3
NT and barrier layer on the Ti-Ta or Ti-Mo alloy
47 gcm3 respectively According to EDS results in Table 1Ti Ti-20Ta Ti-10Ta and Ti-10Mo formed 100 TiO
2 839
TiO2+ 161 Ta
2O5 913 TiO
2+ 87 Ta
2O5 and 928
TiO2+ 72MoO
3The densities of 100TiO
2 839TiO
2+
161 Ta2O5 913 TiO
2+ 87 Ta
2O5 and 928 TiO
2+
72 MoO3were 423 gcm3 484 gcm3 454 gcm3 and
424 gcm3 respectively Therefore the mass of nanotubesfilms 1 cm2 sample for each alloy was listed in Table 2 being532mgcm2 609mgcm2 572mgcm2 and 534mgcm2
Cyclic voltammograms (CV) are used to characterize thecapacitors behavior of the alloy oxide nanotubes Figure 9shows capacitance performance evaluations for the Ti alloyanodic oxide nanotubes by cyclic voltammograms It is clearthat Ti alloy oxide nanotubes had larger area of CV curvethan pure TiO
2nanotube did It means that Ti alloys oxide
nanotubes had larger capacitances than pure TiO2nanotubes
Besides more Ta2O5content can significantly enhance the
capacitor performance by comparing two Ti-Ta alloys curveswith different compositions Moreover Ti-10Mo alloy oxidenanotubes CV curve shows a symmetrical shape whichindicates that the revisable redox reaction of Mo2+Mo3+ washelpful to improve the capacitor performance The specificcapacitance (119862) can bemeasured by voltage step current stepor voltage ramp methods and evaluated by the equations of119862 = 119876119881 and 119862 = 119889119876119889119881 [35] where 119881 is applied voltageand 119876 is the quantity of charge on the electrode (whichcan be evaluated from the area of the CV curve) Table 2shows the specific capacitance based on 1 cm2 sample areaand 20120583m film thickness of pure Ti Ti-20Ta Ti-10Ta andTi-10Mo oxide nanotubes films which are 137 Fg 261 Fg233 Fg and 214 Fg respectively The specific capacitancesof Ti alloys oxide nanotubes films were higher than thatof TiO
2-B nanowiresMWCNTs hybrid supercapacitor with
specific capacitance of 177 Fg [36]
4 Conclusions
In summary we fabricated ultracapacitors based on thework-ing electrode made of highly ordered anodic TiO
2 Ta2O5
and MoO3nanotubes directly formed on pure Ti Ti-20Ta
Ti-10Ta and Ti-10Mo substrates The ordered alloys oxidenanotubes structure has a volume of 126 times 10minus3 cm3 in 1 cm2sample area with nanotube density of 45 times 109 tubescm2The mass of pure Ti and Ti alloys oxide nanotubes films with1 cm2 sample size and 20120583m film thickness can be calcu-lated as 532mg (TiO
2nanotubes) 609mg (Ti-20Ta oxide
nanotubes) 572mg (Ti-10Ta oxide nanotubes) and 534mg
8 Journal of Nanomaterials
H
W
R1
R2
R3
(a)
Top
Bottom
R1
R2
T1
T2
(b)
L
Inne
r sur
face
2120587R1
2120587R2
(c)
Out
er su
rface
H+W
4radic3(R1 + T1)
(d)
Figure 7 Estimation of TiO2NT surface (a) cone structure of inner
tube with radius of 1198773 and 119877
1 and 119877
2on the tube top and bottom
tube length with 119867 (b) pore wall thickness with 1198791and 119879
2on the
tube top and bottom (c) tube inner surface area and (d) outersurface area
0
500
1000
1500
2000
2500
0 25 50 75 100
Outer surface area
Inner surface area
Length (120583m)
Surfa
ce ar
ea (c
m2)
Figure 8 Accumulated anodic Ti and Ti alloy NT inner and outersurface areas based on 1 cm2 substrate
0
2
4
01SEC (V)
minus11minus6
minus4
minus2
minus08 minus05 minus02
Curr
ent d
ensit
y (m
Ac
m2)
TiO2
Ti-10MoO3
TiO2-10Ta2O5TiO2-20Ta2O5
Figure 9 Capacitance performance evaluations for TiO2NT TiO
2-
10 Ta2O5NT TiO
2-20 Ta
2O5NT and TiO
2-10 MoO
3NT by cyclic
voltammograms
(Ti-10Mo oxide nanotubes) respectively Furthermore Tialloy anodic oxide nanotubes films with 1 cm2 surface and20120583m thickness have an inner surface area of 2410 cm2 andouter surface area of 4804 cm2 Thus such large surface areaof dielectric oxides caused very high specific capacitancesThe specific capacitance can further be enhanced by (1)reacting with barium nitrate (Ba(NO
3)2) [37] or barium
hydroxide (Ba(OH)2) [38] to form a very high dielectric
constant BaTiO3film (2) increasing nanotubes length by
longer anodization process and (3) increasing nanotubessurface area by coating TiO
2nanoparticles on the nanotubes
surface [39]
Acknowledgment
This study was partially supported by a Grant from theNational Science Council Taiwan (102-3113-P-042A-005-)
References
[1] L E Cross ldquoFerroelectric materials for electromechanicaltransducer applicationsrdquo Materials Chemistry and Physics vol43 no 2 pp 108ndash115 1996
[2] A D Hilton and R Frost ldquoRecent developments in the manu-facture of barium titanate powdersrdquo Key Engineering Materialsvol 66 pp 145ndash184 1992
[3] L E Cross ldquoDielectric piezoelectric and ferroelectric compo-nentsrdquo American Ceramic Society Bulletin vol 63 no 4 pp586ndash590 1984
[4] D Pandey A P Singh and V S Tiwari ldquoDevelopments inferroelectric ceramics for capacitor applicationsrdquo Bulletin ofMaterials Science vol 15 no 5 pp 391ndash402 1992
[5] K Kajiyoshi N Ishizawa and M Yoshimura ldquoPreparation oftetragonal barium titanate thin film on titaniummetal substrateby hydrothermal methodrdquo Journal of the American CeramicSociety vol 74 no 2 pp 369ndash374 1991
[6] T Horikawa N Mikami T Makita et al ldquoDielectric propertiesof (Ba Sr)TiO
3thin films deposited by RF sputteringrdquo Japanese
Journal of Applied Physics vol 32 no 9 pp 4126ndash4130 1993
Journal of Nanomaterials 9
[7] A S Shaikh and G M Vest ldquoKinetics of BaTiO3and PbTiO
3
formation from metallo-organic precursorsrdquo Journal of theAmerican Ceramic Society vol 69 no 9 pp 682ndash688 1986
[8] H Okamura andH K Bowen ldquoPreparation of alkoxides for thesynthesis of ceramicsrdquo Ceramics International vol 12 no 3 pp161ndash171 1986
[9] K W Kirby ldquoAlkoxide synthesis techniques for BaTiO3rdquoMate-
rials Research Bulletin vol 23 no 6 pp 881ndash890 1988[10] P Bhattacharya T Komeda K-H Park and Y Nishioka
ldquoComparative study of amorphous and crystalline (Ba Sr)TiO3
thin films deposited by laser ablationrdquo Japanese Journal ofApplied Physics vol 32 no 9 pp 4103ndash4106 1993
[11] D M Tahan A Safari and L C Klein ldquoPreparation and char-acterization of Ba
119909Sr1minus119909
TiO3thin films by a Sol-Gel techniquerdquo
Journal of the American Ceramic Society vol 79 no 6 pp 1593ndash1598 1996
[12] C-C Chen J-H Chen C-G Chao and W C Say ldquoElectro-chemical characteristics of surface of titanium formed by elec-trolytic polishing and anodizingrdquo Journal of Materials Sciencevol 40 no 15 pp 4053ndash4059 2005
[13] C-C Chen Y Bisrat Z P Luo R E Schaak C-G Chao andD C Lagoudas ldquoFabrication of single-crystal tin nanowires byhydraulic pressure injectionrdquo Nanotechnology vol 17 no 2 pp367ndash374 2006
[14] H Tsuchiya and P Schmuki ldquoSelf-organized high aspect ratioporous hafnium oxide prepared by electrochemical anodiza-tionrdquo Electrochemistry Communications vol 7 no 1 pp 49ndash522005
[15] I Sieber H Hildebrand A Friedrich and P Schmuki ldquoForma-tion of self-organized niobium porous oxide on niobiumrdquo Elec-trochemistry Communications vol 7 no 1 pp 97ndash100 2005
[16] I Sieber B Kannan and P Schmuki ldquoSelf-assembled poroustantalum oxide prepared in H
2SO4HF electrolytesrdquo Electro-
chemical and Solid-State Letters vol 8 no 3 pp J10ndashJ12 2005[17] N Mukherjee M Paulose O K Varghese G K Mor and
C A Grimes ldquoFabrication of nanoporous tungsten oxide bygalvanostatic anodizationrdquo Journal ofMaterials Research vol 18no 10 pp 2296ndash2299 2003
[18] G B Stefanovich A L Pergament A A Velichko and L AStefanovich ldquoAnodic oxidation of vanadium and properties ofvanadium oxide filmsrdquo Journal of Physics Condensed Mattervol 16 no 23 pp 4013ndash4024 2004
[19] N K Shrestha Y-C Nah H Tsuchiya and P SchmukildquoSelf-organized nano-tubes of TiO
2-MoO
3with enhanced elec-
trochromic propertiesrdquo Chemical Communications no 15 pp2008ndash2010 2009
[20] I Paramasivam Y-C Nah C Das N K Shrestha and PSchmuki ldquoWO
3TiO2nanotubes with strongly enhanced pho-
tocatalytic activityrdquoChemistrymdashA European Journal vol 16 no30 pp 8993ndash8997 2010
[21] A Ghicov S Aldabergenova H Tsuchyia and P SchmukildquoTiO2-Nb2O5nanotubes with electrochemically tunable mor-
phologiesrdquo Angewandte ChemiemdashInternational Edition vol 45no 42 pp 6993ndash6996 2006
[22] Y Yang D Kim M Yang and P Schmuki ldquoVertically alignedmixed V
2O5-TiO2nanotube arrays for supercapacitor applica-
tionsrdquoChemical Communications vol 47 no 27 pp 7746ndash77482011
[23] H Jha R Hahn and P Schmuki ldquoUltrafast oxide nanotube for-mation on TiNb TiZr and TiTa alloys by rapid breakdown an-odizationrdquo Electrochimica Acta vol 55 no 28 pp 8883ndash88872010
[24] WWei S Berger N Shrestha and P Schmuki ldquoIdeal hexagonalorder formation of self-organized anodic oxide nanotubes andnanopores on a Ti-35Ta alloyrdquo Journal of the ElectrochemicalSociety vol 157 no 12 pp C409ndashC413 2010
[25] H Tsuchiya S Berger J M Macak A Ghicov and P SchmukildquoSelf-organized porous and tubular oxide layers on TiAl alloysrdquoElectrochemistry Communications vol 9 no 9 pp 2397ndash24022007
[26] R J D Tilley ldquoCorrelation between dielectric constant anddefect structure of non-stoichiometric solidsrdquo Nature vol 269no 5625 pp 229ndash231 1977
[27] J Lin N Masaaki A Tsukune and M Yamada ldquoTa2O5thin
films with exceptionally high dielectric constantrdquo Applied Phys-ics Letters vol 74 no 16 pp 2370ndash2372 1999
[28] H Segawa K Mori M Itagati K Sakurki and T Ishiwta ldquoIm-age sensing devicerdquo US patent no 4499384 1985
[29] C C Chen D Fang and Z Luo ldquoFabrication and characteriza-tion of highly-ordered valve-metal oxide nanotubes and theirderivative nanostructuresrdquo Reviews in Nanoscience and Nan-otechnology vol 1 no 4 pp 1ndash28 2012
[30] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions NACE Houston Tex USA 1974
[31] C W Lai and S Sreekantan ldquoEffect of applied potential onthe formation of self-organized TiO
2nanotube arrays and its
photoelectrochemical responserdquo Journal of Nanomaterials vol2011 Article ID 142463 7 pages 2011
[32] J H Lim and J Choi ldquoTitanium oxide nanowires originat-ing from anodically grown nanotubes the bamboo-splittingmodelrdquo Small vol 3 no 9 pp 1504ndash1507 2007
[33] J Tao J Zhao X Wang Y Kang and Y Li ldquoFabrication oftitania nanotube arrays on curved surfacerdquo ElectrochemistryCommunications vol 10 no 8 pp 1161ndash1163 2008
[34] D Kim F Schmidt-Stein R Hahn and P Schmuki ldquoGravityassisted growth of self-organized anodic oxide nanotubes ontitaniumrdquo Electrochemistry Communications vol 10 no 7 pp1082ndash1086 2008
[35] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons Singapore 1980
[36] G Wang Z Y Liu J N Wu and Q Lu ldquoPreparation and elec-trochemical capacitance behavior of TiO
2-B nanotubes for hy-
brid supercapacitorrdquoMaterials Letters vol 71 pp 120ndash122 2012[37] L Zhang Y Shi S Peng J Liang Z Tao and J Chen ldquoDye-
sensitized solar cells made from BaTiO3-coated TiO
2nano-
porous electrodesrdquo Journal of Photochemistry and PhotobiologyA vol 197 no 2-3 pp 260ndash265 2008
[38] XWei ldquoHydrothermal synthesis of BaTiO3thin films on nano-
porous TiO2covered Ti substratesrdquo Journal of Crystal Growth
vol 286 no 2 pp 371ndash375 2006[39] C-C Chen H-W Chung C-H Chen et al ldquoFabrication and
characterization of anodic titanium oxide nanotube arrays ofcontrolled length for highly efficient dye-sensitized solar cellsrdquoJournal of Physical Chemistry C vol 112 no 48 pp 19151ndash191572008
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
2 Journal of Nanomaterials
135120583m
(a)
135120583m
(b)
05 120583m
(c)
135120583m
(d)
05 120583m
(e)
05 120583m
(f)
Figure 1 SEM images of TiO2NT (a) an unwanted film cover onTiO
2NT (b) partial unwanted film removed (c) all unwanted films removed
and TiO2NT presented (d) TiO
2NT side view (e) TiO
2NT bottom view and (f) a barrier layer on the TiO
2NT bottom
Ti + 10wt Ta) Ti-20Ta (80wt Ti + 20wt Ta) andTi-10Mo (90wt Ti + 10wt Mo) alloys The metal sub-strates were first put through electropolishing (EP) The EPelectrolyte included 5 volperchloric acid (HClO
4) 53 vol
ethylene glycol monobutylether (HOCH2CH2OC4H9) and
42 vol methanol (CH3OH) EP processes of Ti and Ti
alloys were conducted at 15∘C under 52V for 1 minute and28V for 13 minutes with platinum as a counter electrodeat a constant stirring rate of 200 rpm After EP the sampleswere etched in 5 vol HF for 5min to form an additionalthin anodic film on the metal substrates TiO
2 TiO2-Ta2O5
and TiO2-MoO
3nanotubes were anodized in an electrolyte
of 05 wt ammonium fluoride (NH4F 999) and 2wt
H2O in ethylene glycol (C
2H4(OH)2) solvent at a constant
voltage of 60V for 2 hours After anodic films were formedby anodization the films were then annealed in an airfurnace at 450∘C for 1 hour for crystallization The surfacemorphologies of the anodic oxides were observed by usinga scanning electron microscope (SEM FEI Quanta 600)The alloy oxide nanotubes compositions can be analyzed byEnergy Dispersive Spectrometer (EDS) (Oxford)
Cyclic voltammetry (CV) performances were evaluatedby an electrochemical analyzer (CH Instruments Model600B USA) using a standard three-electrode cell systemwithplatinum as a counter electrode and silver-silver chlorideelectrode (AgAgCl) as a reference electrode in 05M H
2SO4
solution at room temperature The CV scan rate was set as20mVs in a potential range of 0V to 09V (AgAgCl)
Journal of Nanomaterials 3
16
06
2 146 10Ti
pH
TiO
minus2
minus04
minus14
minus24
TiO3+3
TiO2+
Ti3+
Ti2+ Ti(OH)3
HTiOminus3
HTiOminus4
Ti(OH)4
E(V
)
TiO3middot2H2O
(a)
pH
0
1
2
0 4 8 12
Ta
TaO+2 Ta2O5
E(V
)
minus1
minus2
(b)
pH
02
07
12
0 3 6 9 12
Mo
H2MoO4
MoO3
MoO2minus4
MoO2
E(V
)
minus08
minus03 Mo3+
(c)
Figure 2 Pourbaix diagrams of (a) Ti (b) Ta and (c) Mo
3 Results and Discussion
Figure 1 presents the SEM images of long-range orderednanochannel TiO
2NT structures formed by anodizing pure
Ti foil (a) an unwanted film covered on TiO2NT (b) partial
unwanted film removed (c) all unwanted films removed andthe top view of TiO
2NT (d) side view of TiO
2NT (e) bottom
view of TiO2NT and (f) a barrier layer under the TiO
2NT
TiO2NT feature a pore diameter sim120 nm pore density sim8
times 109 porescm2 and wall thickness sim25 nm the length ofthe NT can be controlled from several 120583ms to hundred 120583mswith different types of the electrolytes (eg NH
4F) and the
anodization times at a constant applied voltage (eg 60V)Immersing titanium in electrolyte causes complex reac-
tions with 16 forms of Ti ions and oxides [29] The Pourbaixdiagram is useful to simplify the complex reactions [30]Based on the Pourbaix diagram of Ti (Figure 2(a)) TiO2+ion is a favorite formation when pH value is lower than 23and voltage is higher than minus02 V (SHE) at 25∘C TiO2+ canfurther react with H
2O to from Ti(OH)
4which is anodic
titanium oxide Similarly Ta Pourbaix diagram (Figure 2(b))shows that TiO2+ is formed and converted to Ta
2O5under the
condition of pH lt 51 and applying voltage gtminus12 V (SHE) atroom temperature Also Mo Pourbaix diagram (Figure 2(c))implies that Mo3+ can be produced and form MoO
3in the
condition of pH being below 42 and voltage being higherthan minus035V (SHE) at 25∘C However anodic TiO
2 MoO
3
and Ta2O5can be formed in the neutral pH value electrolyte
when it contains halogen element in it
Anodization of titanium forms close-packed and vertical-aligned nanotubes in a nonaqueous organic polar electrolytewith Fminus ions and minimizing water content These electro-chemical processes can be described as follows [31ndash34]
Ti 997888rarr Ti4+ + 4eminus (1)
H2O 997888rarr 2H++O2minus (2)
Ti4+ + 2O2minus997888rarr TiO2 (3)
Ti4+ + 2H2O 997888rarr 4H++ TiO2 (4)
6Fminus + TiO2 + 4H+997888rarr [TiF6]
2minus+ 2H2O (5)
[TiF6]2minus+ 119899H2O 997888rarr [TiF6minus119899(OH)
119899]2minus + 119899H+
+ 119899Fminus (6)
[TiF6minus119899(OH)119899]
2minus+ (6 minus 119899)H2O
997888rarr [Ti(OH)6]
2minus+ (6 minus 119899)H+ + (6 minus 119899) Fminus
(7)
[Ti(OH)6]
2minus+ 2H+ 997888rarr TiO
2+ 4H2O (8)
During anodization there are oxidation reactions at theinterface between metal and electrolyte Ti4+ is formed andthe water in the electrolyte is decomposed reactions (1) and(2) TiO
2is then formed between themetal and the electrolyte
through ion migration reactions (3) and (4) Fminus ions etch theTiO2forming [TiF
6]2minus and then combine with the H
2O to
form [TiF6minus119899(OH)119899]
2minus reactions (5) and (6) Because the Fminusions are doped in the TiO
2but do not form a compound
reaction (6) can be rewritten as (7) Finally [Ti(OH)6]
2minus
reacts with 2H+ to form TiO2nanotubes reaction (8)
4 Journal of Nanomaterials
10120583m
(a)
1120583m
(b)
125 120583m
(c)
125 120583m
(d)
05 120583m
(e)
Figure 3 SEM images of Ti-Ta NT film structure (a) compact layer (b) partial porous film (c) porous film (d) net film and (e) Ti-Ta NT
Based on reactions (1)ndash(8) anodization of Ta can bedescribed as
Ta 997888rarr Ta5+ + 5eminus (9)
H2O 997888rarr 2H++O2minus (10)
2Ta5+ + 5O2minus 997888rarr Ta2O5 (11)
2Ta5+ + 5H2O 997888rarr 10H+ + Ta
2O5
(12)
12Fminus + 2Ta2O5+ 10H+ 997888rarr 2[TaF
6]
minus+ 5H2O (13)
2[TaF6]
minus+ 2119899H
2O 997888rarr 2[TaF
6minus2119899(OH)2119899]
minus+ 2119899H+ + 2119899Fminus
(14)
2[TaF6minus2119899(OH)2119899]
minus+ (6 minus 2119899)H2O
997888rarr [Ta(OH)6]
minus+ (6 minus 2119899)H+ + (6 minus 2119899) Fminus
(15)
2[Ta(OH)6]
minus+ 2H+ 997888rarr Ta
2O5+ 7H2O (16)
Journal of Nanomaterials 5
1120583m
(a)
1120583m
(b)
1120583m
(c)
1120583m
(d)
Figure 4 SEM images of TiO2-Ta2O5nanotubes film by anodizing Ti-20Ta alloy (a) a net film on the NT top (b) without a net film on the
NT top (c) a barrier layer on the NT bottom and (d) partial barrier layer on the NT bottom
Also anodization of Mo can be described as
Mo 997888rarr Mo3+ + 3eminus (17)
H2O 997888rarr 2H++O2minus (18)
Mo3+ + 3O2minus 997888rarr MoO3
(19)
Mo3+ + 3H2O 997888rarr 6H++MoO
3(20)
6Fminus +MoO3+ 6H+ 997888rarr [MoF
6]
3minus+ 3H2O (21)
[MoF6]
3minus+ 119899H2O 997888rarr [MoF
6minus119899(OH)119899]
3minus+ 119899H+ + 119899Fminus
(22)
[MoF6minus119899(OH)119899]
3minus+ (6 minus 119899)H2O
997888rarr [Mo(OH)6]
3minus+ (6 minus 119899)H+ + (6 minus 119899) Fminus
(23)
[Mo(OH)6]
3minus+ 3H+ 997888rarr MoO
3+ 3H2O (24)
Figure 3 shows SEM images of TiO2-Ta2O5nanotubes
structure from anodizing Ti-10Ta alloy There was a compactlayer on the top of nanotubes in Figure 3(a) A continuousporous layer and grain boundary under the compact layer
are observed in Figure 3(b) Figure 3(c) shows a porous filmis covering the compact layer and following a net structure(Figure 3(d)) is covering the gap between ordered TiO
2-
Ta2O5nanotubes (Figure 3(e)) There were extra continuous
porous layers and net structures which were not presented onpure TiO
2nanotubes The compact layer continuous porous
layer andnet structurewere removed by 5wtof 1120583mAl2O3
powders in ethanol solvent assisted by ultrasonic vibrationSimilar to Ti-10Ta alloy Figure 4 shows SEM images ofTiO2-Ta2O5nanotube by anodizingTi-20Ta alloy Figure 4(a)
shows a net film on the NT top Figure 4(b) without a net filmon the NT top Figure 4(c) a barrier layer on the NT bottomand Figure 4(d) partial barrier layer under the NT
For the Ti-10Mo alloy Figure 5(a) shows partially re-moved continuous porous layer on the net structure largerpores on the top of TiO
2-MoO
3nanotubes (Figure 5(b))
smaller pores (Figure 5(c)) and barrier layer (Figure 5(d))on the bottom side According to Figures 3ndash5 Figure 6 is aschematic diagram of anodic Ti alloy oxide structure withcompact layer continuous porous layer net structure andordered nanotubes on the alloys surfaces
Figure 7 shows a schematic structure and geometry ofthe Ti alloy oxide nanotube Larger open pores are on the
6 Journal of Nanomaterials
125 120583m
(a)
05 120583m
(b)
1120583m
(c)
125 120583m
(d)
Figure 5 SEM images of TiO2-MoO
3nanotubes film by anodizing Ti-10Mo alloy (a) a porous film and a net film on theNT top (b) a cleaned
NT top (c) small pores on the NT bottom and (d) a barrier layer on the NT bottom
Table 1 EDS results of Ti alloys oxide nanotubes
TiO2 () Ta2O5 () MoO3 ()Ti-20Ta 839 161 0Ti-10Ta 913 87 0Ti-10Mo 928 0 72
top (Figure 7(a)) smaller closed pores and a barrier layerin a hexagonal pattern are on the bottom side (Figure 7(b))tube inner surface area (Figure 7(c)) and outer surfacearea (Figure 7(d)) Denoting 119877
1and 119877
2 and 119879
1and 119879
2are
the radius and pores width of the top and bottom poresrespective119882 is the thickness of the outer barrier layer and119867 and 119871 is the inner height and total length of the nanotubeWe have 119877
1+ 1198791= 1198772+ 1198792= 1198773 and total length of nanotube
is 119871 = 119867+119882 Thus the volume of a single alloy oxide can becalculated by119881 = 119881outer minus119881inner where119881outer and119881inner can beobtained by
119881outer = 1205871198772
3times 119871
119881inner =1
3
120587 times
119867
119877
1minus 119877
2
times (119877
3
1minus 119877
3
2)
(25)
Based on the SEM images in Figures 3 4 and 5119877111987721198773
and 119882 were 60 nm 25 nm 80 nm and 40 nm respectivelyFor two hours anodization process 20120583m length of Ti alloyoxide nanotubes (119871) could be formed on the Ti alloy surfaceThus 119881outer was 04120583m
3 and 119881inner was 012 120583m3 and the
volume of a single alloy oxide nanotube (119881) was 028120583m3The TiO
2nanotubes density has been recently reported by
Chen et al [29] such that there are 4510548978 nanotubesper cm2 Therefore the total volume of Ti alloy nanotubeswas 126 times 10minus3 cm3 in 1 cm2 sample area Moreover it hasalso been reported that nanotube surface area is greatlyincreased when 119871 = 10 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 and 119871 = 100 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 Figure 8 furthermore accumulated anodic Ti andTi alloy NT inner and outer surface areas increased withfilm thickness increased based on 1 cm2 substrate Hence theextremely high surface area is able to provide more chancesfor electrochemical reactions
According to the Pourbaix diagrams in Figure 2 anodiz-ing Ti Ti-20Ta Ti-10Ta and Ti-10Mo can form anodic oxidefilms of these Ti alloys Therefore the following alloy anodicoxide films densities are able to be calculated based on theTiO2 Ta2O5 andMoO
3densities of 42 gcm3 82 gcm3 and
Journal of Nanomaterials 7
Table 2 Specific capacitance based on TiO2 NT Ti-10Ta NT Ti-20Ta NT and Ti-10Mo NT films
Sample size (1 cm2times 20 120583m) TiO2 NT Ti-10Ta NT Ti-20Ta NT Ti-10Mo NT
Density (gcm2) 309 319 365 307Mass of unit area (mgcm2) 618 638 730 614119889119876 (mC) 6558 12002 14330 10292119889119864 (V) 09 09 09 09Specific capacitance (Fg) 118 209 218 186
(a)
(b)
(c)
(d)
Ti-Ta or Ti-Mo alloy
Barrier layer
TiO2-Ta2O5NT or TiO2-MoO3 NT
(e)
Figure 6The schematic diagram of TiO2-Ta2O5NT or TiO
2-MoO
3
NT film structure (a) compact layer (b) partial porous film (c)porous film (d) net film and (e) TiO
2-Ta2O5NT or TiO
2-MoO
3
NT and barrier layer on the Ti-Ta or Ti-Mo alloy
47 gcm3 respectively According to EDS results in Table 1Ti Ti-20Ta Ti-10Ta and Ti-10Mo formed 100 TiO
2 839
TiO2+ 161 Ta
2O5 913 TiO
2+ 87 Ta
2O5 and 928
TiO2+ 72MoO
3The densities of 100TiO
2 839TiO
2+
161 Ta2O5 913 TiO
2+ 87 Ta
2O5 and 928 TiO
2+
72 MoO3were 423 gcm3 484 gcm3 454 gcm3 and
424 gcm3 respectively Therefore the mass of nanotubesfilms 1 cm2 sample for each alloy was listed in Table 2 being532mgcm2 609mgcm2 572mgcm2 and 534mgcm2
Cyclic voltammograms (CV) are used to characterize thecapacitors behavior of the alloy oxide nanotubes Figure 9shows capacitance performance evaluations for the Ti alloyanodic oxide nanotubes by cyclic voltammograms It is clearthat Ti alloy oxide nanotubes had larger area of CV curvethan pure TiO
2nanotube did It means that Ti alloys oxide
nanotubes had larger capacitances than pure TiO2nanotubes
Besides more Ta2O5content can significantly enhance the
capacitor performance by comparing two Ti-Ta alloys curveswith different compositions Moreover Ti-10Mo alloy oxidenanotubes CV curve shows a symmetrical shape whichindicates that the revisable redox reaction of Mo2+Mo3+ washelpful to improve the capacitor performance The specificcapacitance (119862) can bemeasured by voltage step current stepor voltage ramp methods and evaluated by the equations of119862 = 119876119881 and 119862 = 119889119876119889119881 [35] where 119881 is applied voltageand 119876 is the quantity of charge on the electrode (whichcan be evaluated from the area of the CV curve) Table 2shows the specific capacitance based on 1 cm2 sample areaand 20120583m film thickness of pure Ti Ti-20Ta Ti-10Ta andTi-10Mo oxide nanotubes films which are 137 Fg 261 Fg233 Fg and 214 Fg respectively The specific capacitancesof Ti alloys oxide nanotubes films were higher than thatof TiO
2-B nanowiresMWCNTs hybrid supercapacitor with
specific capacitance of 177 Fg [36]
4 Conclusions
In summary we fabricated ultracapacitors based on thework-ing electrode made of highly ordered anodic TiO
2 Ta2O5
and MoO3nanotubes directly formed on pure Ti Ti-20Ta
Ti-10Ta and Ti-10Mo substrates The ordered alloys oxidenanotubes structure has a volume of 126 times 10minus3 cm3 in 1 cm2sample area with nanotube density of 45 times 109 tubescm2The mass of pure Ti and Ti alloys oxide nanotubes films with1 cm2 sample size and 20120583m film thickness can be calcu-lated as 532mg (TiO
2nanotubes) 609mg (Ti-20Ta oxide
nanotubes) 572mg (Ti-10Ta oxide nanotubes) and 534mg
8 Journal of Nanomaterials
H
W
R1
R2
R3
(a)
Top
Bottom
R1
R2
T1
T2
(b)
L
Inne
r sur
face
2120587R1
2120587R2
(c)
Out
er su
rface
H+W
4radic3(R1 + T1)
(d)
Figure 7 Estimation of TiO2NT surface (a) cone structure of inner
tube with radius of 1198773 and 119877
1 and 119877
2on the tube top and bottom
tube length with 119867 (b) pore wall thickness with 1198791and 119879
2on the
tube top and bottom (c) tube inner surface area and (d) outersurface area
0
500
1000
1500
2000
2500
0 25 50 75 100
Outer surface area
Inner surface area
Length (120583m)
Surfa
ce ar
ea (c
m2)
Figure 8 Accumulated anodic Ti and Ti alloy NT inner and outersurface areas based on 1 cm2 substrate
0
2
4
01SEC (V)
minus11minus6
minus4
minus2
minus08 minus05 minus02
Curr
ent d
ensit
y (m
Ac
m2)
TiO2
Ti-10MoO3
TiO2-10Ta2O5TiO2-20Ta2O5
Figure 9 Capacitance performance evaluations for TiO2NT TiO
2-
10 Ta2O5NT TiO
2-20 Ta
2O5NT and TiO
2-10 MoO
3NT by cyclic
voltammograms
(Ti-10Mo oxide nanotubes) respectively Furthermore Tialloy anodic oxide nanotubes films with 1 cm2 surface and20120583m thickness have an inner surface area of 2410 cm2 andouter surface area of 4804 cm2 Thus such large surface areaof dielectric oxides caused very high specific capacitancesThe specific capacitance can further be enhanced by (1)reacting with barium nitrate (Ba(NO
3)2) [37] or barium
hydroxide (Ba(OH)2) [38] to form a very high dielectric
constant BaTiO3film (2) increasing nanotubes length by
longer anodization process and (3) increasing nanotubessurface area by coating TiO
2nanoparticles on the nanotubes
surface [39]
Acknowledgment
This study was partially supported by a Grant from theNational Science Council Taiwan (102-3113-P-042A-005-)
References
[1] L E Cross ldquoFerroelectric materials for electromechanicaltransducer applicationsrdquo Materials Chemistry and Physics vol43 no 2 pp 108ndash115 1996
[2] A D Hilton and R Frost ldquoRecent developments in the manu-facture of barium titanate powdersrdquo Key Engineering Materialsvol 66 pp 145ndash184 1992
[3] L E Cross ldquoDielectric piezoelectric and ferroelectric compo-nentsrdquo American Ceramic Society Bulletin vol 63 no 4 pp586ndash590 1984
[4] D Pandey A P Singh and V S Tiwari ldquoDevelopments inferroelectric ceramics for capacitor applicationsrdquo Bulletin ofMaterials Science vol 15 no 5 pp 391ndash402 1992
[5] K Kajiyoshi N Ishizawa and M Yoshimura ldquoPreparation oftetragonal barium titanate thin film on titaniummetal substrateby hydrothermal methodrdquo Journal of the American CeramicSociety vol 74 no 2 pp 369ndash374 1991
[6] T Horikawa N Mikami T Makita et al ldquoDielectric propertiesof (Ba Sr)TiO
3thin films deposited by RF sputteringrdquo Japanese
Journal of Applied Physics vol 32 no 9 pp 4126ndash4130 1993
Journal of Nanomaterials 9
[7] A S Shaikh and G M Vest ldquoKinetics of BaTiO3and PbTiO
3
formation from metallo-organic precursorsrdquo Journal of theAmerican Ceramic Society vol 69 no 9 pp 682ndash688 1986
[8] H Okamura andH K Bowen ldquoPreparation of alkoxides for thesynthesis of ceramicsrdquo Ceramics International vol 12 no 3 pp161ndash171 1986
[9] K W Kirby ldquoAlkoxide synthesis techniques for BaTiO3rdquoMate-
rials Research Bulletin vol 23 no 6 pp 881ndash890 1988[10] P Bhattacharya T Komeda K-H Park and Y Nishioka
ldquoComparative study of amorphous and crystalline (Ba Sr)TiO3
thin films deposited by laser ablationrdquo Japanese Journal ofApplied Physics vol 32 no 9 pp 4103ndash4106 1993
[11] D M Tahan A Safari and L C Klein ldquoPreparation and char-acterization of Ba
119909Sr1minus119909
TiO3thin films by a Sol-Gel techniquerdquo
Journal of the American Ceramic Society vol 79 no 6 pp 1593ndash1598 1996
[12] C-C Chen J-H Chen C-G Chao and W C Say ldquoElectro-chemical characteristics of surface of titanium formed by elec-trolytic polishing and anodizingrdquo Journal of Materials Sciencevol 40 no 15 pp 4053ndash4059 2005
[13] C-C Chen Y Bisrat Z P Luo R E Schaak C-G Chao andD C Lagoudas ldquoFabrication of single-crystal tin nanowires byhydraulic pressure injectionrdquo Nanotechnology vol 17 no 2 pp367ndash374 2006
[14] H Tsuchiya and P Schmuki ldquoSelf-organized high aspect ratioporous hafnium oxide prepared by electrochemical anodiza-tionrdquo Electrochemistry Communications vol 7 no 1 pp 49ndash522005
[15] I Sieber H Hildebrand A Friedrich and P Schmuki ldquoForma-tion of self-organized niobium porous oxide on niobiumrdquo Elec-trochemistry Communications vol 7 no 1 pp 97ndash100 2005
[16] I Sieber B Kannan and P Schmuki ldquoSelf-assembled poroustantalum oxide prepared in H
2SO4HF electrolytesrdquo Electro-
chemical and Solid-State Letters vol 8 no 3 pp J10ndashJ12 2005[17] N Mukherjee M Paulose O K Varghese G K Mor and
C A Grimes ldquoFabrication of nanoporous tungsten oxide bygalvanostatic anodizationrdquo Journal ofMaterials Research vol 18no 10 pp 2296ndash2299 2003
[18] G B Stefanovich A L Pergament A A Velichko and L AStefanovich ldquoAnodic oxidation of vanadium and properties ofvanadium oxide filmsrdquo Journal of Physics Condensed Mattervol 16 no 23 pp 4013ndash4024 2004
[19] N K Shrestha Y-C Nah H Tsuchiya and P SchmukildquoSelf-organized nano-tubes of TiO
2-MoO
3with enhanced elec-
trochromic propertiesrdquo Chemical Communications no 15 pp2008ndash2010 2009
[20] I Paramasivam Y-C Nah C Das N K Shrestha and PSchmuki ldquoWO
3TiO2nanotubes with strongly enhanced pho-
tocatalytic activityrdquoChemistrymdashA European Journal vol 16 no30 pp 8993ndash8997 2010
[21] A Ghicov S Aldabergenova H Tsuchyia and P SchmukildquoTiO2-Nb2O5nanotubes with electrochemically tunable mor-
phologiesrdquo Angewandte ChemiemdashInternational Edition vol 45no 42 pp 6993ndash6996 2006
[22] Y Yang D Kim M Yang and P Schmuki ldquoVertically alignedmixed V
2O5-TiO2nanotube arrays for supercapacitor applica-
tionsrdquoChemical Communications vol 47 no 27 pp 7746ndash77482011
[23] H Jha R Hahn and P Schmuki ldquoUltrafast oxide nanotube for-mation on TiNb TiZr and TiTa alloys by rapid breakdown an-odizationrdquo Electrochimica Acta vol 55 no 28 pp 8883ndash88872010
[24] WWei S Berger N Shrestha and P Schmuki ldquoIdeal hexagonalorder formation of self-organized anodic oxide nanotubes andnanopores on a Ti-35Ta alloyrdquo Journal of the ElectrochemicalSociety vol 157 no 12 pp C409ndashC413 2010
[25] H Tsuchiya S Berger J M Macak A Ghicov and P SchmukildquoSelf-organized porous and tubular oxide layers on TiAl alloysrdquoElectrochemistry Communications vol 9 no 9 pp 2397ndash24022007
[26] R J D Tilley ldquoCorrelation between dielectric constant anddefect structure of non-stoichiometric solidsrdquo Nature vol 269no 5625 pp 229ndash231 1977
[27] J Lin N Masaaki A Tsukune and M Yamada ldquoTa2O5thin
films with exceptionally high dielectric constantrdquo Applied Phys-ics Letters vol 74 no 16 pp 2370ndash2372 1999
[28] H Segawa K Mori M Itagati K Sakurki and T Ishiwta ldquoIm-age sensing devicerdquo US patent no 4499384 1985
[29] C C Chen D Fang and Z Luo ldquoFabrication and characteriza-tion of highly-ordered valve-metal oxide nanotubes and theirderivative nanostructuresrdquo Reviews in Nanoscience and Nan-otechnology vol 1 no 4 pp 1ndash28 2012
[30] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions NACE Houston Tex USA 1974
[31] C W Lai and S Sreekantan ldquoEffect of applied potential onthe formation of self-organized TiO
2nanotube arrays and its
photoelectrochemical responserdquo Journal of Nanomaterials vol2011 Article ID 142463 7 pages 2011
[32] J H Lim and J Choi ldquoTitanium oxide nanowires originat-ing from anodically grown nanotubes the bamboo-splittingmodelrdquo Small vol 3 no 9 pp 1504ndash1507 2007
[33] J Tao J Zhao X Wang Y Kang and Y Li ldquoFabrication oftitania nanotube arrays on curved surfacerdquo ElectrochemistryCommunications vol 10 no 8 pp 1161ndash1163 2008
[34] D Kim F Schmidt-Stein R Hahn and P Schmuki ldquoGravityassisted growth of self-organized anodic oxide nanotubes ontitaniumrdquo Electrochemistry Communications vol 10 no 7 pp1082ndash1086 2008
[35] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons Singapore 1980
[36] G Wang Z Y Liu J N Wu and Q Lu ldquoPreparation and elec-trochemical capacitance behavior of TiO
2-B nanotubes for hy-
brid supercapacitorrdquoMaterials Letters vol 71 pp 120ndash122 2012[37] L Zhang Y Shi S Peng J Liang Z Tao and J Chen ldquoDye-
sensitized solar cells made from BaTiO3-coated TiO
2nano-
porous electrodesrdquo Journal of Photochemistry and PhotobiologyA vol 197 no 2-3 pp 260ndash265 2008
[38] XWei ldquoHydrothermal synthesis of BaTiO3thin films on nano-
porous TiO2covered Ti substratesrdquo Journal of Crystal Growth
vol 286 no 2 pp 371ndash375 2006[39] C-C Chen H-W Chung C-H Chen et al ldquoFabrication and
characterization of anodic titanium oxide nanotube arrays ofcontrolled length for highly efficient dye-sensitized solar cellsrdquoJournal of Physical Chemistry C vol 112 no 48 pp 19151ndash191572008
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Journal of Nanomaterials 3
16
06
2 146 10Ti
pH
TiO
minus2
minus04
minus14
minus24
TiO3+3
TiO2+
Ti3+
Ti2+ Ti(OH)3
HTiOminus3
HTiOminus4
Ti(OH)4
E(V
)
TiO3middot2H2O
(a)
pH
0
1
2
0 4 8 12
Ta
TaO+2 Ta2O5
E(V
)
minus1
minus2
(b)
pH
02
07
12
0 3 6 9 12
Mo
H2MoO4
MoO3
MoO2minus4
MoO2
E(V
)
minus08
minus03 Mo3+
(c)
Figure 2 Pourbaix diagrams of (a) Ti (b) Ta and (c) Mo
3 Results and Discussion
Figure 1 presents the SEM images of long-range orderednanochannel TiO
2NT structures formed by anodizing pure
Ti foil (a) an unwanted film covered on TiO2NT (b) partial
unwanted film removed (c) all unwanted films removed andthe top view of TiO
2NT (d) side view of TiO
2NT (e) bottom
view of TiO2NT and (f) a barrier layer under the TiO
2NT
TiO2NT feature a pore diameter sim120 nm pore density sim8
times 109 porescm2 and wall thickness sim25 nm the length ofthe NT can be controlled from several 120583ms to hundred 120583mswith different types of the electrolytes (eg NH
4F) and the
anodization times at a constant applied voltage (eg 60V)Immersing titanium in electrolyte causes complex reac-
tions with 16 forms of Ti ions and oxides [29] The Pourbaixdiagram is useful to simplify the complex reactions [30]Based on the Pourbaix diagram of Ti (Figure 2(a)) TiO2+ion is a favorite formation when pH value is lower than 23and voltage is higher than minus02 V (SHE) at 25∘C TiO2+ canfurther react with H
2O to from Ti(OH)
4which is anodic
titanium oxide Similarly Ta Pourbaix diagram (Figure 2(b))shows that TiO2+ is formed and converted to Ta
2O5under the
condition of pH lt 51 and applying voltage gtminus12 V (SHE) atroom temperature Also Mo Pourbaix diagram (Figure 2(c))implies that Mo3+ can be produced and form MoO
3in the
condition of pH being below 42 and voltage being higherthan minus035V (SHE) at 25∘C However anodic TiO
2 MoO
3
and Ta2O5can be formed in the neutral pH value electrolyte
when it contains halogen element in it
Anodization of titanium forms close-packed and vertical-aligned nanotubes in a nonaqueous organic polar electrolytewith Fminus ions and minimizing water content These electro-chemical processes can be described as follows [31ndash34]
Ti 997888rarr Ti4+ + 4eminus (1)
H2O 997888rarr 2H++O2minus (2)
Ti4+ + 2O2minus997888rarr TiO2 (3)
Ti4+ + 2H2O 997888rarr 4H++ TiO2 (4)
6Fminus + TiO2 + 4H+997888rarr [TiF6]
2minus+ 2H2O (5)
[TiF6]2minus+ 119899H2O 997888rarr [TiF6minus119899(OH)
119899]2minus + 119899H+
+ 119899Fminus (6)
[TiF6minus119899(OH)119899]
2minus+ (6 minus 119899)H2O
997888rarr [Ti(OH)6]
2minus+ (6 minus 119899)H+ + (6 minus 119899) Fminus
(7)
[Ti(OH)6]
2minus+ 2H+ 997888rarr TiO
2+ 4H2O (8)
During anodization there are oxidation reactions at theinterface between metal and electrolyte Ti4+ is formed andthe water in the electrolyte is decomposed reactions (1) and(2) TiO
2is then formed between themetal and the electrolyte
through ion migration reactions (3) and (4) Fminus ions etch theTiO2forming [TiF
6]2minus and then combine with the H
2O to
form [TiF6minus119899(OH)119899]
2minus reactions (5) and (6) Because the Fminusions are doped in the TiO
2but do not form a compound
reaction (6) can be rewritten as (7) Finally [Ti(OH)6]
2minus
reacts with 2H+ to form TiO2nanotubes reaction (8)
4 Journal of Nanomaterials
10120583m
(a)
1120583m
(b)
125 120583m
(c)
125 120583m
(d)
05 120583m
(e)
Figure 3 SEM images of Ti-Ta NT film structure (a) compact layer (b) partial porous film (c) porous film (d) net film and (e) Ti-Ta NT
Based on reactions (1)ndash(8) anodization of Ta can bedescribed as
Ta 997888rarr Ta5+ + 5eminus (9)
H2O 997888rarr 2H++O2minus (10)
2Ta5+ + 5O2minus 997888rarr Ta2O5 (11)
2Ta5+ + 5H2O 997888rarr 10H+ + Ta
2O5
(12)
12Fminus + 2Ta2O5+ 10H+ 997888rarr 2[TaF
6]
minus+ 5H2O (13)
2[TaF6]
minus+ 2119899H
2O 997888rarr 2[TaF
6minus2119899(OH)2119899]
minus+ 2119899H+ + 2119899Fminus
(14)
2[TaF6minus2119899(OH)2119899]
minus+ (6 minus 2119899)H2O
997888rarr [Ta(OH)6]
minus+ (6 minus 2119899)H+ + (6 minus 2119899) Fminus
(15)
2[Ta(OH)6]
minus+ 2H+ 997888rarr Ta
2O5+ 7H2O (16)
Journal of Nanomaterials 5
1120583m
(a)
1120583m
(b)
1120583m
(c)
1120583m
(d)
Figure 4 SEM images of TiO2-Ta2O5nanotubes film by anodizing Ti-20Ta alloy (a) a net film on the NT top (b) without a net film on the
NT top (c) a barrier layer on the NT bottom and (d) partial barrier layer on the NT bottom
Also anodization of Mo can be described as
Mo 997888rarr Mo3+ + 3eminus (17)
H2O 997888rarr 2H++O2minus (18)
Mo3+ + 3O2minus 997888rarr MoO3
(19)
Mo3+ + 3H2O 997888rarr 6H++MoO
3(20)
6Fminus +MoO3+ 6H+ 997888rarr [MoF
6]
3minus+ 3H2O (21)
[MoF6]
3minus+ 119899H2O 997888rarr [MoF
6minus119899(OH)119899]
3minus+ 119899H+ + 119899Fminus
(22)
[MoF6minus119899(OH)119899]
3minus+ (6 minus 119899)H2O
997888rarr [Mo(OH)6]
3minus+ (6 minus 119899)H+ + (6 minus 119899) Fminus
(23)
[Mo(OH)6]
3minus+ 3H+ 997888rarr MoO
3+ 3H2O (24)
Figure 3 shows SEM images of TiO2-Ta2O5nanotubes
structure from anodizing Ti-10Ta alloy There was a compactlayer on the top of nanotubes in Figure 3(a) A continuousporous layer and grain boundary under the compact layer
are observed in Figure 3(b) Figure 3(c) shows a porous filmis covering the compact layer and following a net structure(Figure 3(d)) is covering the gap between ordered TiO
2-
Ta2O5nanotubes (Figure 3(e)) There were extra continuous
porous layers and net structures which were not presented onpure TiO
2nanotubes The compact layer continuous porous
layer andnet structurewere removed by 5wtof 1120583mAl2O3
powders in ethanol solvent assisted by ultrasonic vibrationSimilar to Ti-10Ta alloy Figure 4 shows SEM images ofTiO2-Ta2O5nanotube by anodizingTi-20Ta alloy Figure 4(a)
shows a net film on the NT top Figure 4(b) without a net filmon the NT top Figure 4(c) a barrier layer on the NT bottomand Figure 4(d) partial barrier layer under the NT
For the Ti-10Mo alloy Figure 5(a) shows partially re-moved continuous porous layer on the net structure largerpores on the top of TiO
2-MoO
3nanotubes (Figure 5(b))
smaller pores (Figure 5(c)) and barrier layer (Figure 5(d))on the bottom side According to Figures 3ndash5 Figure 6 is aschematic diagram of anodic Ti alloy oxide structure withcompact layer continuous porous layer net structure andordered nanotubes on the alloys surfaces
Figure 7 shows a schematic structure and geometry ofthe Ti alloy oxide nanotube Larger open pores are on the
6 Journal of Nanomaterials
125 120583m
(a)
05 120583m
(b)
1120583m
(c)
125 120583m
(d)
Figure 5 SEM images of TiO2-MoO
3nanotubes film by anodizing Ti-10Mo alloy (a) a porous film and a net film on theNT top (b) a cleaned
NT top (c) small pores on the NT bottom and (d) a barrier layer on the NT bottom
Table 1 EDS results of Ti alloys oxide nanotubes
TiO2 () Ta2O5 () MoO3 ()Ti-20Ta 839 161 0Ti-10Ta 913 87 0Ti-10Mo 928 0 72
top (Figure 7(a)) smaller closed pores and a barrier layerin a hexagonal pattern are on the bottom side (Figure 7(b))tube inner surface area (Figure 7(c)) and outer surfacearea (Figure 7(d)) Denoting 119877
1and 119877
2 and 119879
1and 119879
2are
the radius and pores width of the top and bottom poresrespective119882 is the thickness of the outer barrier layer and119867 and 119871 is the inner height and total length of the nanotubeWe have 119877
1+ 1198791= 1198772+ 1198792= 1198773 and total length of nanotube
is 119871 = 119867+119882 Thus the volume of a single alloy oxide can becalculated by119881 = 119881outer minus119881inner where119881outer and119881inner can beobtained by
119881outer = 1205871198772
3times 119871
119881inner =1
3
120587 times
119867
119877
1minus 119877
2
times (119877
3
1minus 119877
3
2)
(25)
Based on the SEM images in Figures 3 4 and 5119877111987721198773
and 119882 were 60 nm 25 nm 80 nm and 40 nm respectivelyFor two hours anodization process 20120583m length of Ti alloyoxide nanotubes (119871) could be formed on the Ti alloy surfaceThus 119881outer was 04120583m
3 and 119881inner was 012 120583m3 and the
volume of a single alloy oxide nanotube (119881) was 028120583m3The TiO
2nanotubes density has been recently reported by
Chen et al [29] such that there are 4510548978 nanotubesper cm2 Therefore the total volume of Ti alloy nanotubeswas 126 times 10minus3 cm3 in 1 cm2 sample area Moreover it hasalso been reported that nanotube surface area is greatlyincreased when 119871 = 10 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 and 119871 = 100 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 Figure 8 furthermore accumulated anodic Ti andTi alloy NT inner and outer surface areas increased withfilm thickness increased based on 1 cm2 substrate Hence theextremely high surface area is able to provide more chancesfor electrochemical reactions
According to the Pourbaix diagrams in Figure 2 anodiz-ing Ti Ti-20Ta Ti-10Ta and Ti-10Mo can form anodic oxidefilms of these Ti alloys Therefore the following alloy anodicoxide films densities are able to be calculated based on theTiO2 Ta2O5 andMoO
3densities of 42 gcm3 82 gcm3 and
Journal of Nanomaterials 7
Table 2 Specific capacitance based on TiO2 NT Ti-10Ta NT Ti-20Ta NT and Ti-10Mo NT films
Sample size (1 cm2times 20 120583m) TiO2 NT Ti-10Ta NT Ti-20Ta NT Ti-10Mo NT
Density (gcm2) 309 319 365 307Mass of unit area (mgcm2) 618 638 730 614119889119876 (mC) 6558 12002 14330 10292119889119864 (V) 09 09 09 09Specific capacitance (Fg) 118 209 218 186
(a)
(b)
(c)
(d)
Ti-Ta or Ti-Mo alloy
Barrier layer
TiO2-Ta2O5NT or TiO2-MoO3 NT
(e)
Figure 6The schematic diagram of TiO2-Ta2O5NT or TiO
2-MoO
3
NT film structure (a) compact layer (b) partial porous film (c)porous film (d) net film and (e) TiO
2-Ta2O5NT or TiO
2-MoO
3
NT and barrier layer on the Ti-Ta or Ti-Mo alloy
47 gcm3 respectively According to EDS results in Table 1Ti Ti-20Ta Ti-10Ta and Ti-10Mo formed 100 TiO
2 839
TiO2+ 161 Ta
2O5 913 TiO
2+ 87 Ta
2O5 and 928
TiO2+ 72MoO
3The densities of 100TiO
2 839TiO
2+
161 Ta2O5 913 TiO
2+ 87 Ta
2O5 and 928 TiO
2+
72 MoO3were 423 gcm3 484 gcm3 454 gcm3 and
424 gcm3 respectively Therefore the mass of nanotubesfilms 1 cm2 sample for each alloy was listed in Table 2 being532mgcm2 609mgcm2 572mgcm2 and 534mgcm2
Cyclic voltammograms (CV) are used to characterize thecapacitors behavior of the alloy oxide nanotubes Figure 9shows capacitance performance evaluations for the Ti alloyanodic oxide nanotubes by cyclic voltammograms It is clearthat Ti alloy oxide nanotubes had larger area of CV curvethan pure TiO
2nanotube did It means that Ti alloys oxide
nanotubes had larger capacitances than pure TiO2nanotubes
Besides more Ta2O5content can significantly enhance the
capacitor performance by comparing two Ti-Ta alloys curveswith different compositions Moreover Ti-10Mo alloy oxidenanotubes CV curve shows a symmetrical shape whichindicates that the revisable redox reaction of Mo2+Mo3+ washelpful to improve the capacitor performance The specificcapacitance (119862) can bemeasured by voltage step current stepor voltage ramp methods and evaluated by the equations of119862 = 119876119881 and 119862 = 119889119876119889119881 [35] where 119881 is applied voltageand 119876 is the quantity of charge on the electrode (whichcan be evaluated from the area of the CV curve) Table 2shows the specific capacitance based on 1 cm2 sample areaand 20120583m film thickness of pure Ti Ti-20Ta Ti-10Ta andTi-10Mo oxide nanotubes films which are 137 Fg 261 Fg233 Fg and 214 Fg respectively The specific capacitancesof Ti alloys oxide nanotubes films were higher than thatof TiO
2-B nanowiresMWCNTs hybrid supercapacitor with
specific capacitance of 177 Fg [36]
4 Conclusions
In summary we fabricated ultracapacitors based on thework-ing electrode made of highly ordered anodic TiO
2 Ta2O5
and MoO3nanotubes directly formed on pure Ti Ti-20Ta
Ti-10Ta and Ti-10Mo substrates The ordered alloys oxidenanotubes structure has a volume of 126 times 10minus3 cm3 in 1 cm2sample area with nanotube density of 45 times 109 tubescm2The mass of pure Ti and Ti alloys oxide nanotubes films with1 cm2 sample size and 20120583m film thickness can be calcu-lated as 532mg (TiO
2nanotubes) 609mg (Ti-20Ta oxide
nanotubes) 572mg (Ti-10Ta oxide nanotubes) and 534mg
8 Journal of Nanomaterials
H
W
R1
R2
R3
(a)
Top
Bottom
R1
R2
T1
T2
(b)
L
Inne
r sur
face
2120587R1
2120587R2
(c)
Out
er su
rface
H+W
4radic3(R1 + T1)
(d)
Figure 7 Estimation of TiO2NT surface (a) cone structure of inner
tube with radius of 1198773 and 119877
1 and 119877
2on the tube top and bottom
tube length with 119867 (b) pore wall thickness with 1198791and 119879
2on the
tube top and bottom (c) tube inner surface area and (d) outersurface area
0
500
1000
1500
2000
2500
0 25 50 75 100
Outer surface area
Inner surface area
Length (120583m)
Surfa
ce ar
ea (c
m2)
Figure 8 Accumulated anodic Ti and Ti alloy NT inner and outersurface areas based on 1 cm2 substrate
0
2
4
01SEC (V)
minus11minus6
minus4
minus2
minus08 minus05 minus02
Curr
ent d
ensit
y (m
Ac
m2)
TiO2
Ti-10MoO3
TiO2-10Ta2O5TiO2-20Ta2O5
Figure 9 Capacitance performance evaluations for TiO2NT TiO
2-
10 Ta2O5NT TiO
2-20 Ta
2O5NT and TiO
2-10 MoO
3NT by cyclic
voltammograms
(Ti-10Mo oxide nanotubes) respectively Furthermore Tialloy anodic oxide nanotubes films with 1 cm2 surface and20120583m thickness have an inner surface area of 2410 cm2 andouter surface area of 4804 cm2 Thus such large surface areaof dielectric oxides caused very high specific capacitancesThe specific capacitance can further be enhanced by (1)reacting with barium nitrate (Ba(NO
3)2) [37] or barium
hydroxide (Ba(OH)2) [38] to form a very high dielectric
constant BaTiO3film (2) increasing nanotubes length by
longer anodization process and (3) increasing nanotubessurface area by coating TiO
2nanoparticles on the nanotubes
surface [39]
Acknowledgment
This study was partially supported by a Grant from theNational Science Council Taiwan (102-3113-P-042A-005-)
References
[1] L E Cross ldquoFerroelectric materials for electromechanicaltransducer applicationsrdquo Materials Chemistry and Physics vol43 no 2 pp 108ndash115 1996
[2] A D Hilton and R Frost ldquoRecent developments in the manu-facture of barium titanate powdersrdquo Key Engineering Materialsvol 66 pp 145ndash184 1992
[3] L E Cross ldquoDielectric piezoelectric and ferroelectric compo-nentsrdquo American Ceramic Society Bulletin vol 63 no 4 pp586ndash590 1984
[4] D Pandey A P Singh and V S Tiwari ldquoDevelopments inferroelectric ceramics for capacitor applicationsrdquo Bulletin ofMaterials Science vol 15 no 5 pp 391ndash402 1992
[5] K Kajiyoshi N Ishizawa and M Yoshimura ldquoPreparation oftetragonal barium titanate thin film on titaniummetal substrateby hydrothermal methodrdquo Journal of the American CeramicSociety vol 74 no 2 pp 369ndash374 1991
[6] T Horikawa N Mikami T Makita et al ldquoDielectric propertiesof (Ba Sr)TiO
3thin films deposited by RF sputteringrdquo Japanese
Journal of Applied Physics vol 32 no 9 pp 4126ndash4130 1993
Journal of Nanomaterials 9
[7] A S Shaikh and G M Vest ldquoKinetics of BaTiO3and PbTiO
3
formation from metallo-organic precursorsrdquo Journal of theAmerican Ceramic Society vol 69 no 9 pp 682ndash688 1986
[8] H Okamura andH K Bowen ldquoPreparation of alkoxides for thesynthesis of ceramicsrdquo Ceramics International vol 12 no 3 pp161ndash171 1986
[9] K W Kirby ldquoAlkoxide synthesis techniques for BaTiO3rdquoMate-
rials Research Bulletin vol 23 no 6 pp 881ndash890 1988[10] P Bhattacharya T Komeda K-H Park and Y Nishioka
ldquoComparative study of amorphous and crystalline (Ba Sr)TiO3
thin films deposited by laser ablationrdquo Japanese Journal ofApplied Physics vol 32 no 9 pp 4103ndash4106 1993
[11] D M Tahan A Safari and L C Klein ldquoPreparation and char-acterization of Ba
119909Sr1minus119909
TiO3thin films by a Sol-Gel techniquerdquo
Journal of the American Ceramic Society vol 79 no 6 pp 1593ndash1598 1996
[12] C-C Chen J-H Chen C-G Chao and W C Say ldquoElectro-chemical characteristics of surface of titanium formed by elec-trolytic polishing and anodizingrdquo Journal of Materials Sciencevol 40 no 15 pp 4053ndash4059 2005
[13] C-C Chen Y Bisrat Z P Luo R E Schaak C-G Chao andD C Lagoudas ldquoFabrication of single-crystal tin nanowires byhydraulic pressure injectionrdquo Nanotechnology vol 17 no 2 pp367ndash374 2006
[14] H Tsuchiya and P Schmuki ldquoSelf-organized high aspect ratioporous hafnium oxide prepared by electrochemical anodiza-tionrdquo Electrochemistry Communications vol 7 no 1 pp 49ndash522005
[15] I Sieber H Hildebrand A Friedrich and P Schmuki ldquoForma-tion of self-organized niobium porous oxide on niobiumrdquo Elec-trochemistry Communications vol 7 no 1 pp 97ndash100 2005
[16] I Sieber B Kannan and P Schmuki ldquoSelf-assembled poroustantalum oxide prepared in H
2SO4HF electrolytesrdquo Electro-
chemical and Solid-State Letters vol 8 no 3 pp J10ndashJ12 2005[17] N Mukherjee M Paulose O K Varghese G K Mor and
C A Grimes ldquoFabrication of nanoporous tungsten oxide bygalvanostatic anodizationrdquo Journal ofMaterials Research vol 18no 10 pp 2296ndash2299 2003
[18] G B Stefanovich A L Pergament A A Velichko and L AStefanovich ldquoAnodic oxidation of vanadium and properties ofvanadium oxide filmsrdquo Journal of Physics Condensed Mattervol 16 no 23 pp 4013ndash4024 2004
[19] N K Shrestha Y-C Nah H Tsuchiya and P SchmukildquoSelf-organized nano-tubes of TiO
2-MoO
3with enhanced elec-
trochromic propertiesrdquo Chemical Communications no 15 pp2008ndash2010 2009
[20] I Paramasivam Y-C Nah C Das N K Shrestha and PSchmuki ldquoWO
3TiO2nanotubes with strongly enhanced pho-
tocatalytic activityrdquoChemistrymdashA European Journal vol 16 no30 pp 8993ndash8997 2010
[21] A Ghicov S Aldabergenova H Tsuchyia and P SchmukildquoTiO2-Nb2O5nanotubes with electrochemically tunable mor-
phologiesrdquo Angewandte ChemiemdashInternational Edition vol 45no 42 pp 6993ndash6996 2006
[22] Y Yang D Kim M Yang and P Schmuki ldquoVertically alignedmixed V
2O5-TiO2nanotube arrays for supercapacitor applica-
tionsrdquoChemical Communications vol 47 no 27 pp 7746ndash77482011
[23] H Jha R Hahn and P Schmuki ldquoUltrafast oxide nanotube for-mation on TiNb TiZr and TiTa alloys by rapid breakdown an-odizationrdquo Electrochimica Acta vol 55 no 28 pp 8883ndash88872010
[24] WWei S Berger N Shrestha and P Schmuki ldquoIdeal hexagonalorder formation of self-organized anodic oxide nanotubes andnanopores on a Ti-35Ta alloyrdquo Journal of the ElectrochemicalSociety vol 157 no 12 pp C409ndashC413 2010
[25] H Tsuchiya S Berger J M Macak A Ghicov and P SchmukildquoSelf-organized porous and tubular oxide layers on TiAl alloysrdquoElectrochemistry Communications vol 9 no 9 pp 2397ndash24022007
[26] R J D Tilley ldquoCorrelation between dielectric constant anddefect structure of non-stoichiometric solidsrdquo Nature vol 269no 5625 pp 229ndash231 1977
[27] J Lin N Masaaki A Tsukune and M Yamada ldquoTa2O5thin
films with exceptionally high dielectric constantrdquo Applied Phys-ics Letters vol 74 no 16 pp 2370ndash2372 1999
[28] H Segawa K Mori M Itagati K Sakurki and T Ishiwta ldquoIm-age sensing devicerdquo US patent no 4499384 1985
[29] C C Chen D Fang and Z Luo ldquoFabrication and characteriza-tion of highly-ordered valve-metal oxide nanotubes and theirderivative nanostructuresrdquo Reviews in Nanoscience and Nan-otechnology vol 1 no 4 pp 1ndash28 2012
[30] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions NACE Houston Tex USA 1974
[31] C W Lai and S Sreekantan ldquoEffect of applied potential onthe formation of self-organized TiO
2nanotube arrays and its
photoelectrochemical responserdquo Journal of Nanomaterials vol2011 Article ID 142463 7 pages 2011
[32] J H Lim and J Choi ldquoTitanium oxide nanowires originat-ing from anodically grown nanotubes the bamboo-splittingmodelrdquo Small vol 3 no 9 pp 1504ndash1507 2007
[33] J Tao J Zhao X Wang Y Kang and Y Li ldquoFabrication oftitania nanotube arrays on curved surfacerdquo ElectrochemistryCommunications vol 10 no 8 pp 1161ndash1163 2008
[34] D Kim F Schmidt-Stein R Hahn and P Schmuki ldquoGravityassisted growth of self-organized anodic oxide nanotubes ontitaniumrdquo Electrochemistry Communications vol 10 no 7 pp1082ndash1086 2008
[35] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons Singapore 1980
[36] G Wang Z Y Liu J N Wu and Q Lu ldquoPreparation and elec-trochemical capacitance behavior of TiO
2-B nanotubes for hy-
brid supercapacitorrdquoMaterials Letters vol 71 pp 120ndash122 2012[37] L Zhang Y Shi S Peng J Liang Z Tao and J Chen ldquoDye-
sensitized solar cells made from BaTiO3-coated TiO
2nano-
porous electrodesrdquo Journal of Photochemistry and PhotobiologyA vol 197 no 2-3 pp 260ndash265 2008
[38] XWei ldquoHydrothermal synthesis of BaTiO3thin films on nano-
porous TiO2covered Ti substratesrdquo Journal of Crystal Growth
vol 286 no 2 pp 371ndash375 2006[39] C-C Chen H-W Chung C-H Chen et al ldquoFabrication and
characterization of anodic titanium oxide nanotube arrays ofcontrolled length for highly efficient dye-sensitized solar cellsrdquoJournal of Physical Chemistry C vol 112 no 48 pp 19151ndash191572008
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
4 Journal of Nanomaterials
10120583m
(a)
1120583m
(b)
125 120583m
(c)
125 120583m
(d)
05 120583m
(e)
Figure 3 SEM images of Ti-Ta NT film structure (a) compact layer (b) partial porous film (c) porous film (d) net film and (e) Ti-Ta NT
Based on reactions (1)ndash(8) anodization of Ta can bedescribed as
Ta 997888rarr Ta5+ + 5eminus (9)
H2O 997888rarr 2H++O2minus (10)
2Ta5+ + 5O2minus 997888rarr Ta2O5 (11)
2Ta5+ + 5H2O 997888rarr 10H+ + Ta
2O5
(12)
12Fminus + 2Ta2O5+ 10H+ 997888rarr 2[TaF
6]
minus+ 5H2O (13)
2[TaF6]
minus+ 2119899H
2O 997888rarr 2[TaF
6minus2119899(OH)2119899]
minus+ 2119899H+ + 2119899Fminus
(14)
2[TaF6minus2119899(OH)2119899]
minus+ (6 minus 2119899)H2O
997888rarr [Ta(OH)6]
minus+ (6 minus 2119899)H+ + (6 minus 2119899) Fminus
(15)
2[Ta(OH)6]
minus+ 2H+ 997888rarr Ta
2O5+ 7H2O (16)
Journal of Nanomaterials 5
1120583m
(a)
1120583m
(b)
1120583m
(c)
1120583m
(d)
Figure 4 SEM images of TiO2-Ta2O5nanotubes film by anodizing Ti-20Ta alloy (a) a net film on the NT top (b) without a net film on the
NT top (c) a barrier layer on the NT bottom and (d) partial barrier layer on the NT bottom
Also anodization of Mo can be described as
Mo 997888rarr Mo3+ + 3eminus (17)
H2O 997888rarr 2H++O2minus (18)
Mo3+ + 3O2minus 997888rarr MoO3
(19)
Mo3+ + 3H2O 997888rarr 6H++MoO
3(20)
6Fminus +MoO3+ 6H+ 997888rarr [MoF
6]
3minus+ 3H2O (21)
[MoF6]
3minus+ 119899H2O 997888rarr [MoF
6minus119899(OH)119899]
3minus+ 119899H+ + 119899Fminus
(22)
[MoF6minus119899(OH)119899]
3minus+ (6 minus 119899)H2O
997888rarr [Mo(OH)6]
3minus+ (6 minus 119899)H+ + (6 minus 119899) Fminus
(23)
[Mo(OH)6]
3minus+ 3H+ 997888rarr MoO
3+ 3H2O (24)
Figure 3 shows SEM images of TiO2-Ta2O5nanotubes
structure from anodizing Ti-10Ta alloy There was a compactlayer on the top of nanotubes in Figure 3(a) A continuousporous layer and grain boundary under the compact layer
are observed in Figure 3(b) Figure 3(c) shows a porous filmis covering the compact layer and following a net structure(Figure 3(d)) is covering the gap between ordered TiO
2-
Ta2O5nanotubes (Figure 3(e)) There were extra continuous
porous layers and net structures which were not presented onpure TiO
2nanotubes The compact layer continuous porous
layer andnet structurewere removed by 5wtof 1120583mAl2O3
powders in ethanol solvent assisted by ultrasonic vibrationSimilar to Ti-10Ta alloy Figure 4 shows SEM images ofTiO2-Ta2O5nanotube by anodizingTi-20Ta alloy Figure 4(a)
shows a net film on the NT top Figure 4(b) without a net filmon the NT top Figure 4(c) a barrier layer on the NT bottomand Figure 4(d) partial barrier layer under the NT
For the Ti-10Mo alloy Figure 5(a) shows partially re-moved continuous porous layer on the net structure largerpores on the top of TiO
2-MoO
3nanotubes (Figure 5(b))
smaller pores (Figure 5(c)) and barrier layer (Figure 5(d))on the bottom side According to Figures 3ndash5 Figure 6 is aschematic diagram of anodic Ti alloy oxide structure withcompact layer continuous porous layer net structure andordered nanotubes on the alloys surfaces
Figure 7 shows a schematic structure and geometry ofthe Ti alloy oxide nanotube Larger open pores are on the
6 Journal of Nanomaterials
125 120583m
(a)
05 120583m
(b)
1120583m
(c)
125 120583m
(d)
Figure 5 SEM images of TiO2-MoO
3nanotubes film by anodizing Ti-10Mo alloy (a) a porous film and a net film on theNT top (b) a cleaned
NT top (c) small pores on the NT bottom and (d) a barrier layer on the NT bottom
Table 1 EDS results of Ti alloys oxide nanotubes
TiO2 () Ta2O5 () MoO3 ()Ti-20Ta 839 161 0Ti-10Ta 913 87 0Ti-10Mo 928 0 72
top (Figure 7(a)) smaller closed pores and a barrier layerin a hexagonal pattern are on the bottom side (Figure 7(b))tube inner surface area (Figure 7(c)) and outer surfacearea (Figure 7(d)) Denoting 119877
1and 119877
2 and 119879
1and 119879
2are
the radius and pores width of the top and bottom poresrespective119882 is the thickness of the outer barrier layer and119867 and 119871 is the inner height and total length of the nanotubeWe have 119877
1+ 1198791= 1198772+ 1198792= 1198773 and total length of nanotube
is 119871 = 119867+119882 Thus the volume of a single alloy oxide can becalculated by119881 = 119881outer minus119881inner where119881outer and119881inner can beobtained by
119881outer = 1205871198772
3times 119871
119881inner =1
3
120587 times
119867
119877
1minus 119877
2
times (119877
3
1minus 119877
3
2)
(25)
Based on the SEM images in Figures 3 4 and 5119877111987721198773
and 119882 were 60 nm 25 nm 80 nm and 40 nm respectivelyFor two hours anodization process 20120583m length of Ti alloyoxide nanotubes (119871) could be formed on the Ti alloy surfaceThus 119881outer was 04120583m
3 and 119881inner was 012 120583m3 and the
volume of a single alloy oxide nanotube (119881) was 028120583m3The TiO
2nanotubes density has been recently reported by
Chen et al [29] such that there are 4510548978 nanotubesper cm2 Therefore the total volume of Ti alloy nanotubeswas 126 times 10minus3 cm3 in 1 cm2 sample area Moreover it hasalso been reported that nanotube surface area is greatlyincreased when 119871 = 10 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 and 119871 = 100 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 Figure 8 furthermore accumulated anodic Ti andTi alloy NT inner and outer surface areas increased withfilm thickness increased based on 1 cm2 substrate Hence theextremely high surface area is able to provide more chancesfor electrochemical reactions
According to the Pourbaix diagrams in Figure 2 anodiz-ing Ti Ti-20Ta Ti-10Ta and Ti-10Mo can form anodic oxidefilms of these Ti alloys Therefore the following alloy anodicoxide films densities are able to be calculated based on theTiO2 Ta2O5 andMoO
3densities of 42 gcm3 82 gcm3 and
Journal of Nanomaterials 7
Table 2 Specific capacitance based on TiO2 NT Ti-10Ta NT Ti-20Ta NT and Ti-10Mo NT films
Sample size (1 cm2times 20 120583m) TiO2 NT Ti-10Ta NT Ti-20Ta NT Ti-10Mo NT
Density (gcm2) 309 319 365 307Mass of unit area (mgcm2) 618 638 730 614119889119876 (mC) 6558 12002 14330 10292119889119864 (V) 09 09 09 09Specific capacitance (Fg) 118 209 218 186
(a)
(b)
(c)
(d)
Ti-Ta or Ti-Mo alloy
Barrier layer
TiO2-Ta2O5NT or TiO2-MoO3 NT
(e)
Figure 6The schematic diagram of TiO2-Ta2O5NT or TiO
2-MoO
3
NT film structure (a) compact layer (b) partial porous film (c)porous film (d) net film and (e) TiO
2-Ta2O5NT or TiO
2-MoO
3
NT and barrier layer on the Ti-Ta or Ti-Mo alloy
47 gcm3 respectively According to EDS results in Table 1Ti Ti-20Ta Ti-10Ta and Ti-10Mo formed 100 TiO
2 839
TiO2+ 161 Ta
2O5 913 TiO
2+ 87 Ta
2O5 and 928
TiO2+ 72MoO
3The densities of 100TiO
2 839TiO
2+
161 Ta2O5 913 TiO
2+ 87 Ta
2O5 and 928 TiO
2+
72 MoO3were 423 gcm3 484 gcm3 454 gcm3 and
424 gcm3 respectively Therefore the mass of nanotubesfilms 1 cm2 sample for each alloy was listed in Table 2 being532mgcm2 609mgcm2 572mgcm2 and 534mgcm2
Cyclic voltammograms (CV) are used to characterize thecapacitors behavior of the alloy oxide nanotubes Figure 9shows capacitance performance evaluations for the Ti alloyanodic oxide nanotubes by cyclic voltammograms It is clearthat Ti alloy oxide nanotubes had larger area of CV curvethan pure TiO
2nanotube did It means that Ti alloys oxide
nanotubes had larger capacitances than pure TiO2nanotubes
Besides more Ta2O5content can significantly enhance the
capacitor performance by comparing two Ti-Ta alloys curveswith different compositions Moreover Ti-10Mo alloy oxidenanotubes CV curve shows a symmetrical shape whichindicates that the revisable redox reaction of Mo2+Mo3+ washelpful to improve the capacitor performance The specificcapacitance (119862) can bemeasured by voltage step current stepor voltage ramp methods and evaluated by the equations of119862 = 119876119881 and 119862 = 119889119876119889119881 [35] where 119881 is applied voltageand 119876 is the quantity of charge on the electrode (whichcan be evaluated from the area of the CV curve) Table 2shows the specific capacitance based on 1 cm2 sample areaand 20120583m film thickness of pure Ti Ti-20Ta Ti-10Ta andTi-10Mo oxide nanotubes films which are 137 Fg 261 Fg233 Fg and 214 Fg respectively The specific capacitancesof Ti alloys oxide nanotubes films were higher than thatof TiO
2-B nanowiresMWCNTs hybrid supercapacitor with
specific capacitance of 177 Fg [36]
4 Conclusions
In summary we fabricated ultracapacitors based on thework-ing electrode made of highly ordered anodic TiO
2 Ta2O5
and MoO3nanotubes directly formed on pure Ti Ti-20Ta
Ti-10Ta and Ti-10Mo substrates The ordered alloys oxidenanotubes structure has a volume of 126 times 10minus3 cm3 in 1 cm2sample area with nanotube density of 45 times 109 tubescm2The mass of pure Ti and Ti alloys oxide nanotubes films with1 cm2 sample size and 20120583m film thickness can be calcu-lated as 532mg (TiO
2nanotubes) 609mg (Ti-20Ta oxide
nanotubes) 572mg (Ti-10Ta oxide nanotubes) and 534mg
8 Journal of Nanomaterials
H
W
R1
R2
R3
(a)
Top
Bottom
R1
R2
T1
T2
(b)
L
Inne
r sur
face
2120587R1
2120587R2
(c)
Out
er su
rface
H+W
4radic3(R1 + T1)
(d)
Figure 7 Estimation of TiO2NT surface (a) cone structure of inner
tube with radius of 1198773 and 119877
1 and 119877
2on the tube top and bottom
tube length with 119867 (b) pore wall thickness with 1198791and 119879
2on the
tube top and bottom (c) tube inner surface area and (d) outersurface area
0
500
1000
1500
2000
2500
0 25 50 75 100
Outer surface area
Inner surface area
Length (120583m)
Surfa
ce ar
ea (c
m2)
Figure 8 Accumulated anodic Ti and Ti alloy NT inner and outersurface areas based on 1 cm2 substrate
0
2
4
01SEC (V)
minus11minus6
minus4
minus2
minus08 minus05 minus02
Curr
ent d
ensit
y (m
Ac
m2)
TiO2
Ti-10MoO3
TiO2-10Ta2O5TiO2-20Ta2O5
Figure 9 Capacitance performance evaluations for TiO2NT TiO
2-
10 Ta2O5NT TiO
2-20 Ta
2O5NT and TiO
2-10 MoO
3NT by cyclic
voltammograms
(Ti-10Mo oxide nanotubes) respectively Furthermore Tialloy anodic oxide nanotubes films with 1 cm2 surface and20120583m thickness have an inner surface area of 2410 cm2 andouter surface area of 4804 cm2 Thus such large surface areaof dielectric oxides caused very high specific capacitancesThe specific capacitance can further be enhanced by (1)reacting with barium nitrate (Ba(NO
3)2) [37] or barium
hydroxide (Ba(OH)2) [38] to form a very high dielectric
constant BaTiO3film (2) increasing nanotubes length by
longer anodization process and (3) increasing nanotubessurface area by coating TiO
2nanoparticles on the nanotubes
surface [39]
Acknowledgment
This study was partially supported by a Grant from theNational Science Council Taiwan (102-3113-P-042A-005-)
References
[1] L E Cross ldquoFerroelectric materials for electromechanicaltransducer applicationsrdquo Materials Chemistry and Physics vol43 no 2 pp 108ndash115 1996
[2] A D Hilton and R Frost ldquoRecent developments in the manu-facture of barium titanate powdersrdquo Key Engineering Materialsvol 66 pp 145ndash184 1992
[3] L E Cross ldquoDielectric piezoelectric and ferroelectric compo-nentsrdquo American Ceramic Society Bulletin vol 63 no 4 pp586ndash590 1984
[4] D Pandey A P Singh and V S Tiwari ldquoDevelopments inferroelectric ceramics for capacitor applicationsrdquo Bulletin ofMaterials Science vol 15 no 5 pp 391ndash402 1992
[5] K Kajiyoshi N Ishizawa and M Yoshimura ldquoPreparation oftetragonal barium titanate thin film on titaniummetal substrateby hydrothermal methodrdquo Journal of the American CeramicSociety vol 74 no 2 pp 369ndash374 1991
[6] T Horikawa N Mikami T Makita et al ldquoDielectric propertiesof (Ba Sr)TiO
3thin films deposited by RF sputteringrdquo Japanese
Journal of Applied Physics vol 32 no 9 pp 4126ndash4130 1993
Journal of Nanomaterials 9
[7] A S Shaikh and G M Vest ldquoKinetics of BaTiO3and PbTiO
3
formation from metallo-organic precursorsrdquo Journal of theAmerican Ceramic Society vol 69 no 9 pp 682ndash688 1986
[8] H Okamura andH K Bowen ldquoPreparation of alkoxides for thesynthesis of ceramicsrdquo Ceramics International vol 12 no 3 pp161ndash171 1986
[9] K W Kirby ldquoAlkoxide synthesis techniques for BaTiO3rdquoMate-
rials Research Bulletin vol 23 no 6 pp 881ndash890 1988[10] P Bhattacharya T Komeda K-H Park and Y Nishioka
ldquoComparative study of amorphous and crystalline (Ba Sr)TiO3
thin films deposited by laser ablationrdquo Japanese Journal ofApplied Physics vol 32 no 9 pp 4103ndash4106 1993
[11] D M Tahan A Safari and L C Klein ldquoPreparation and char-acterization of Ba
119909Sr1minus119909
TiO3thin films by a Sol-Gel techniquerdquo
Journal of the American Ceramic Society vol 79 no 6 pp 1593ndash1598 1996
[12] C-C Chen J-H Chen C-G Chao and W C Say ldquoElectro-chemical characteristics of surface of titanium formed by elec-trolytic polishing and anodizingrdquo Journal of Materials Sciencevol 40 no 15 pp 4053ndash4059 2005
[13] C-C Chen Y Bisrat Z P Luo R E Schaak C-G Chao andD C Lagoudas ldquoFabrication of single-crystal tin nanowires byhydraulic pressure injectionrdquo Nanotechnology vol 17 no 2 pp367ndash374 2006
[14] H Tsuchiya and P Schmuki ldquoSelf-organized high aspect ratioporous hafnium oxide prepared by electrochemical anodiza-tionrdquo Electrochemistry Communications vol 7 no 1 pp 49ndash522005
[15] I Sieber H Hildebrand A Friedrich and P Schmuki ldquoForma-tion of self-organized niobium porous oxide on niobiumrdquo Elec-trochemistry Communications vol 7 no 1 pp 97ndash100 2005
[16] I Sieber B Kannan and P Schmuki ldquoSelf-assembled poroustantalum oxide prepared in H
2SO4HF electrolytesrdquo Electro-
chemical and Solid-State Letters vol 8 no 3 pp J10ndashJ12 2005[17] N Mukherjee M Paulose O K Varghese G K Mor and
C A Grimes ldquoFabrication of nanoporous tungsten oxide bygalvanostatic anodizationrdquo Journal ofMaterials Research vol 18no 10 pp 2296ndash2299 2003
[18] G B Stefanovich A L Pergament A A Velichko and L AStefanovich ldquoAnodic oxidation of vanadium and properties ofvanadium oxide filmsrdquo Journal of Physics Condensed Mattervol 16 no 23 pp 4013ndash4024 2004
[19] N K Shrestha Y-C Nah H Tsuchiya and P SchmukildquoSelf-organized nano-tubes of TiO
2-MoO
3with enhanced elec-
trochromic propertiesrdquo Chemical Communications no 15 pp2008ndash2010 2009
[20] I Paramasivam Y-C Nah C Das N K Shrestha and PSchmuki ldquoWO
3TiO2nanotubes with strongly enhanced pho-
tocatalytic activityrdquoChemistrymdashA European Journal vol 16 no30 pp 8993ndash8997 2010
[21] A Ghicov S Aldabergenova H Tsuchyia and P SchmukildquoTiO2-Nb2O5nanotubes with electrochemically tunable mor-
phologiesrdquo Angewandte ChemiemdashInternational Edition vol 45no 42 pp 6993ndash6996 2006
[22] Y Yang D Kim M Yang and P Schmuki ldquoVertically alignedmixed V
2O5-TiO2nanotube arrays for supercapacitor applica-
tionsrdquoChemical Communications vol 47 no 27 pp 7746ndash77482011
[23] H Jha R Hahn and P Schmuki ldquoUltrafast oxide nanotube for-mation on TiNb TiZr and TiTa alloys by rapid breakdown an-odizationrdquo Electrochimica Acta vol 55 no 28 pp 8883ndash88872010
[24] WWei S Berger N Shrestha and P Schmuki ldquoIdeal hexagonalorder formation of self-organized anodic oxide nanotubes andnanopores on a Ti-35Ta alloyrdquo Journal of the ElectrochemicalSociety vol 157 no 12 pp C409ndashC413 2010
[25] H Tsuchiya S Berger J M Macak A Ghicov and P SchmukildquoSelf-organized porous and tubular oxide layers on TiAl alloysrdquoElectrochemistry Communications vol 9 no 9 pp 2397ndash24022007
[26] R J D Tilley ldquoCorrelation between dielectric constant anddefect structure of non-stoichiometric solidsrdquo Nature vol 269no 5625 pp 229ndash231 1977
[27] J Lin N Masaaki A Tsukune and M Yamada ldquoTa2O5thin
films with exceptionally high dielectric constantrdquo Applied Phys-ics Letters vol 74 no 16 pp 2370ndash2372 1999
[28] H Segawa K Mori M Itagati K Sakurki and T Ishiwta ldquoIm-age sensing devicerdquo US patent no 4499384 1985
[29] C C Chen D Fang and Z Luo ldquoFabrication and characteriza-tion of highly-ordered valve-metal oxide nanotubes and theirderivative nanostructuresrdquo Reviews in Nanoscience and Nan-otechnology vol 1 no 4 pp 1ndash28 2012
[30] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions NACE Houston Tex USA 1974
[31] C W Lai and S Sreekantan ldquoEffect of applied potential onthe formation of self-organized TiO
2nanotube arrays and its
photoelectrochemical responserdquo Journal of Nanomaterials vol2011 Article ID 142463 7 pages 2011
[32] J H Lim and J Choi ldquoTitanium oxide nanowires originat-ing from anodically grown nanotubes the bamboo-splittingmodelrdquo Small vol 3 no 9 pp 1504ndash1507 2007
[33] J Tao J Zhao X Wang Y Kang and Y Li ldquoFabrication oftitania nanotube arrays on curved surfacerdquo ElectrochemistryCommunications vol 10 no 8 pp 1161ndash1163 2008
[34] D Kim F Schmidt-Stein R Hahn and P Schmuki ldquoGravityassisted growth of self-organized anodic oxide nanotubes ontitaniumrdquo Electrochemistry Communications vol 10 no 7 pp1082ndash1086 2008
[35] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons Singapore 1980
[36] G Wang Z Y Liu J N Wu and Q Lu ldquoPreparation and elec-trochemical capacitance behavior of TiO
2-B nanotubes for hy-
brid supercapacitorrdquoMaterials Letters vol 71 pp 120ndash122 2012[37] L Zhang Y Shi S Peng J Liang Z Tao and J Chen ldquoDye-
sensitized solar cells made from BaTiO3-coated TiO
2nano-
porous electrodesrdquo Journal of Photochemistry and PhotobiologyA vol 197 no 2-3 pp 260ndash265 2008
[38] XWei ldquoHydrothermal synthesis of BaTiO3thin films on nano-
porous TiO2covered Ti substratesrdquo Journal of Crystal Growth
vol 286 no 2 pp 371ndash375 2006[39] C-C Chen H-W Chung C-H Chen et al ldquoFabrication and
characterization of anodic titanium oxide nanotube arrays ofcontrolled length for highly efficient dye-sensitized solar cellsrdquoJournal of Physical Chemistry C vol 112 no 48 pp 19151ndash191572008
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Journal of Nanomaterials 5
1120583m
(a)
1120583m
(b)
1120583m
(c)
1120583m
(d)
Figure 4 SEM images of TiO2-Ta2O5nanotubes film by anodizing Ti-20Ta alloy (a) a net film on the NT top (b) without a net film on the
NT top (c) a barrier layer on the NT bottom and (d) partial barrier layer on the NT bottom
Also anodization of Mo can be described as
Mo 997888rarr Mo3+ + 3eminus (17)
H2O 997888rarr 2H++O2minus (18)
Mo3+ + 3O2minus 997888rarr MoO3
(19)
Mo3+ + 3H2O 997888rarr 6H++MoO
3(20)
6Fminus +MoO3+ 6H+ 997888rarr [MoF
6]
3minus+ 3H2O (21)
[MoF6]
3minus+ 119899H2O 997888rarr [MoF
6minus119899(OH)119899]
3minus+ 119899H+ + 119899Fminus
(22)
[MoF6minus119899(OH)119899]
3minus+ (6 minus 119899)H2O
997888rarr [Mo(OH)6]
3minus+ (6 minus 119899)H+ + (6 minus 119899) Fminus
(23)
[Mo(OH)6]
3minus+ 3H+ 997888rarr MoO
3+ 3H2O (24)
Figure 3 shows SEM images of TiO2-Ta2O5nanotubes
structure from anodizing Ti-10Ta alloy There was a compactlayer on the top of nanotubes in Figure 3(a) A continuousporous layer and grain boundary under the compact layer
are observed in Figure 3(b) Figure 3(c) shows a porous filmis covering the compact layer and following a net structure(Figure 3(d)) is covering the gap between ordered TiO
2-
Ta2O5nanotubes (Figure 3(e)) There were extra continuous
porous layers and net structures which were not presented onpure TiO
2nanotubes The compact layer continuous porous
layer andnet structurewere removed by 5wtof 1120583mAl2O3
powders in ethanol solvent assisted by ultrasonic vibrationSimilar to Ti-10Ta alloy Figure 4 shows SEM images ofTiO2-Ta2O5nanotube by anodizingTi-20Ta alloy Figure 4(a)
shows a net film on the NT top Figure 4(b) without a net filmon the NT top Figure 4(c) a barrier layer on the NT bottomand Figure 4(d) partial barrier layer under the NT
For the Ti-10Mo alloy Figure 5(a) shows partially re-moved continuous porous layer on the net structure largerpores on the top of TiO
2-MoO
3nanotubes (Figure 5(b))
smaller pores (Figure 5(c)) and barrier layer (Figure 5(d))on the bottom side According to Figures 3ndash5 Figure 6 is aschematic diagram of anodic Ti alloy oxide structure withcompact layer continuous porous layer net structure andordered nanotubes on the alloys surfaces
Figure 7 shows a schematic structure and geometry ofthe Ti alloy oxide nanotube Larger open pores are on the
6 Journal of Nanomaterials
125 120583m
(a)
05 120583m
(b)
1120583m
(c)
125 120583m
(d)
Figure 5 SEM images of TiO2-MoO
3nanotubes film by anodizing Ti-10Mo alloy (a) a porous film and a net film on theNT top (b) a cleaned
NT top (c) small pores on the NT bottom and (d) a barrier layer on the NT bottom
Table 1 EDS results of Ti alloys oxide nanotubes
TiO2 () Ta2O5 () MoO3 ()Ti-20Ta 839 161 0Ti-10Ta 913 87 0Ti-10Mo 928 0 72
top (Figure 7(a)) smaller closed pores and a barrier layerin a hexagonal pattern are on the bottom side (Figure 7(b))tube inner surface area (Figure 7(c)) and outer surfacearea (Figure 7(d)) Denoting 119877
1and 119877
2 and 119879
1and 119879
2are
the radius and pores width of the top and bottom poresrespective119882 is the thickness of the outer barrier layer and119867 and 119871 is the inner height and total length of the nanotubeWe have 119877
1+ 1198791= 1198772+ 1198792= 1198773 and total length of nanotube
is 119871 = 119867+119882 Thus the volume of a single alloy oxide can becalculated by119881 = 119881outer minus119881inner where119881outer and119881inner can beobtained by
119881outer = 1205871198772
3times 119871
119881inner =1
3
120587 times
119867
119877
1minus 119877
2
times (119877
3
1minus 119877
3
2)
(25)
Based on the SEM images in Figures 3 4 and 5119877111987721198773
and 119882 were 60 nm 25 nm 80 nm and 40 nm respectivelyFor two hours anodization process 20120583m length of Ti alloyoxide nanotubes (119871) could be formed on the Ti alloy surfaceThus 119881outer was 04120583m
3 and 119881inner was 012 120583m3 and the
volume of a single alloy oxide nanotube (119881) was 028120583m3The TiO
2nanotubes density has been recently reported by
Chen et al [29] such that there are 4510548978 nanotubesper cm2 Therefore the total volume of Ti alloy nanotubeswas 126 times 10minus3 cm3 in 1 cm2 sample area Moreover it hasalso been reported that nanotube surface area is greatlyincreased when 119871 = 10 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 and 119871 = 100 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 Figure 8 furthermore accumulated anodic Ti andTi alloy NT inner and outer surface areas increased withfilm thickness increased based on 1 cm2 substrate Hence theextremely high surface area is able to provide more chancesfor electrochemical reactions
According to the Pourbaix diagrams in Figure 2 anodiz-ing Ti Ti-20Ta Ti-10Ta and Ti-10Mo can form anodic oxidefilms of these Ti alloys Therefore the following alloy anodicoxide films densities are able to be calculated based on theTiO2 Ta2O5 andMoO
3densities of 42 gcm3 82 gcm3 and
Journal of Nanomaterials 7
Table 2 Specific capacitance based on TiO2 NT Ti-10Ta NT Ti-20Ta NT and Ti-10Mo NT films
Sample size (1 cm2times 20 120583m) TiO2 NT Ti-10Ta NT Ti-20Ta NT Ti-10Mo NT
Density (gcm2) 309 319 365 307Mass of unit area (mgcm2) 618 638 730 614119889119876 (mC) 6558 12002 14330 10292119889119864 (V) 09 09 09 09Specific capacitance (Fg) 118 209 218 186
(a)
(b)
(c)
(d)
Ti-Ta or Ti-Mo alloy
Barrier layer
TiO2-Ta2O5NT or TiO2-MoO3 NT
(e)
Figure 6The schematic diagram of TiO2-Ta2O5NT or TiO
2-MoO
3
NT film structure (a) compact layer (b) partial porous film (c)porous film (d) net film and (e) TiO
2-Ta2O5NT or TiO
2-MoO
3
NT and barrier layer on the Ti-Ta or Ti-Mo alloy
47 gcm3 respectively According to EDS results in Table 1Ti Ti-20Ta Ti-10Ta and Ti-10Mo formed 100 TiO
2 839
TiO2+ 161 Ta
2O5 913 TiO
2+ 87 Ta
2O5 and 928
TiO2+ 72MoO
3The densities of 100TiO
2 839TiO
2+
161 Ta2O5 913 TiO
2+ 87 Ta
2O5 and 928 TiO
2+
72 MoO3were 423 gcm3 484 gcm3 454 gcm3 and
424 gcm3 respectively Therefore the mass of nanotubesfilms 1 cm2 sample for each alloy was listed in Table 2 being532mgcm2 609mgcm2 572mgcm2 and 534mgcm2
Cyclic voltammograms (CV) are used to characterize thecapacitors behavior of the alloy oxide nanotubes Figure 9shows capacitance performance evaluations for the Ti alloyanodic oxide nanotubes by cyclic voltammograms It is clearthat Ti alloy oxide nanotubes had larger area of CV curvethan pure TiO
2nanotube did It means that Ti alloys oxide
nanotubes had larger capacitances than pure TiO2nanotubes
Besides more Ta2O5content can significantly enhance the
capacitor performance by comparing two Ti-Ta alloys curveswith different compositions Moreover Ti-10Mo alloy oxidenanotubes CV curve shows a symmetrical shape whichindicates that the revisable redox reaction of Mo2+Mo3+ washelpful to improve the capacitor performance The specificcapacitance (119862) can bemeasured by voltage step current stepor voltage ramp methods and evaluated by the equations of119862 = 119876119881 and 119862 = 119889119876119889119881 [35] where 119881 is applied voltageand 119876 is the quantity of charge on the electrode (whichcan be evaluated from the area of the CV curve) Table 2shows the specific capacitance based on 1 cm2 sample areaand 20120583m film thickness of pure Ti Ti-20Ta Ti-10Ta andTi-10Mo oxide nanotubes films which are 137 Fg 261 Fg233 Fg and 214 Fg respectively The specific capacitancesof Ti alloys oxide nanotubes films were higher than thatof TiO
2-B nanowiresMWCNTs hybrid supercapacitor with
specific capacitance of 177 Fg [36]
4 Conclusions
In summary we fabricated ultracapacitors based on thework-ing electrode made of highly ordered anodic TiO
2 Ta2O5
and MoO3nanotubes directly formed on pure Ti Ti-20Ta
Ti-10Ta and Ti-10Mo substrates The ordered alloys oxidenanotubes structure has a volume of 126 times 10minus3 cm3 in 1 cm2sample area with nanotube density of 45 times 109 tubescm2The mass of pure Ti and Ti alloys oxide nanotubes films with1 cm2 sample size and 20120583m film thickness can be calcu-lated as 532mg (TiO
2nanotubes) 609mg (Ti-20Ta oxide
nanotubes) 572mg (Ti-10Ta oxide nanotubes) and 534mg
8 Journal of Nanomaterials
H
W
R1
R2
R3
(a)
Top
Bottom
R1
R2
T1
T2
(b)
L
Inne
r sur
face
2120587R1
2120587R2
(c)
Out
er su
rface
H+W
4radic3(R1 + T1)
(d)
Figure 7 Estimation of TiO2NT surface (a) cone structure of inner
tube with radius of 1198773 and 119877
1 and 119877
2on the tube top and bottom
tube length with 119867 (b) pore wall thickness with 1198791and 119879
2on the
tube top and bottom (c) tube inner surface area and (d) outersurface area
0
500
1000
1500
2000
2500
0 25 50 75 100
Outer surface area
Inner surface area
Length (120583m)
Surfa
ce ar
ea (c
m2)
Figure 8 Accumulated anodic Ti and Ti alloy NT inner and outersurface areas based on 1 cm2 substrate
0
2
4
01SEC (V)
minus11minus6
minus4
minus2
minus08 minus05 minus02
Curr
ent d
ensit
y (m
Ac
m2)
TiO2
Ti-10MoO3
TiO2-10Ta2O5TiO2-20Ta2O5
Figure 9 Capacitance performance evaluations for TiO2NT TiO
2-
10 Ta2O5NT TiO
2-20 Ta
2O5NT and TiO
2-10 MoO
3NT by cyclic
voltammograms
(Ti-10Mo oxide nanotubes) respectively Furthermore Tialloy anodic oxide nanotubes films with 1 cm2 surface and20120583m thickness have an inner surface area of 2410 cm2 andouter surface area of 4804 cm2 Thus such large surface areaof dielectric oxides caused very high specific capacitancesThe specific capacitance can further be enhanced by (1)reacting with barium nitrate (Ba(NO
3)2) [37] or barium
hydroxide (Ba(OH)2) [38] to form a very high dielectric
constant BaTiO3film (2) increasing nanotubes length by
longer anodization process and (3) increasing nanotubessurface area by coating TiO
2nanoparticles on the nanotubes
surface [39]
Acknowledgment
This study was partially supported by a Grant from theNational Science Council Taiwan (102-3113-P-042A-005-)
References
[1] L E Cross ldquoFerroelectric materials for electromechanicaltransducer applicationsrdquo Materials Chemistry and Physics vol43 no 2 pp 108ndash115 1996
[2] A D Hilton and R Frost ldquoRecent developments in the manu-facture of barium titanate powdersrdquo Key Engineering Materialsvol 66 pp 145ndash184 1992
[3] L E Cross ldquoDielectric piezoelectric and ferroelectric compo-nentsrdquo American Ceramic Society Bulletin vol 63 no 4 pp586ndash590 1984
[4] D Pandey A P Singh and V S Tiwari ldquoDevelopments inferroelectric ceramics for capacitor applicationsrdquo Bulletin ofMaterials Science vol 15 no 5 pp 391ndash402 1992
[5] K Kajiyoshi N Ishizawa and M Yoshimura ldquoPreparation oftetragonal barium titanate thin film on titaniummetal substrateby hydrothermal methodrdquo Journal of the American CeramicSociety vol 74 no 2 pp 369ndash374 1991
[6] T Horikawa N Mikami T Makita et al ldquoDielectric propertiesof (Ba Sr)TiO
3thin films deposited by RF sputteringrdquo Japanese
Journal of Applied Physics vol 32 no 9 pp 4126ndash4130 1993
Journal of Nanomaterials 9
[7] A S Shaikh and G M Vest ldquoKinetics of BaTiO3and PbTiO
3
formation from metallo-organic precursorsrdquo Journal of theAmerican Ceramic Society vol 69 no 9 pp 682ndash688 1986
[8] H Okamura andH K Bowen ldquoPreparation of alkoxides for thesynthesis of ceramicsrdquo Ceramics International vol 12 no 3 pp161ndash171 1986
[9] K W Kirby ldquoAlkoxide synthesis techniques for BaTiO3rdquoMate-
rials Research Bulletin vol 23 no 6 pp 881ndash890 1988[10] P Bhattacharya T Komeda K-H Park and Y Nishioka
ldquoComparative study of amorphous and crystalline (Ba Sr)TiO3
thin films deposited by laser ablationrdquo Japanese Journal ofApplied Physics vol 32 no 9 pp 4103ndash4106 1993
[11] D M Tahan A Safari and L C Klein ldquoPreparation and char-acterization of Ba
119909Sr1minus119909
TiO3thin films by a Sol-Gel techniquerdquo
Journal of the American Ceramic Society vol 79 no 6 pp 1593ndash1598 1996
[12] C-C Chen J-H Chen C-G Chao and W C Say ldquoElectro-chemical characteristics of surface of titanium formed by elec-trolytic polishing and anodizingrdquo Journal of Materials Sciencevol 40 no 15 pp 4053ndash4059 2005
[13] C-C Chen Y Bisrat Z P Luo R E Schaak C-G Chao andD C Lagoudas ldquoFabrication of single-crystal tin nanowires byhydraulic pressure injectionrdquo Nanotechnology vol 17 no 2 pp367ndash374 2006
[14] H Tsuchiya and P Schmuki ldquoSelf-organized high aspect ratioporous hafnium oxide prepared by electrochemical anodiza-tionrdquo Electrochemistry Communications vol 7 no 1 pp 49ndash522005
[15] I Sieber H Hildebrand A Friedrich and P Schmuki ldquoForma-tion of self-organized niobium porous oxide on niobiumrdquo Elec-trochemistry Communications vol 7 no 1 pp 97ndash100 2005
[16] I Sieber B Kannan and P Schmuki ldquoSelf-assembled poroustantalum oxide prepared in H
2SO4HF electrolytesrdquo Electro-
chemical and Solid-State Letters vol 8 no 3 pp J10ndashJ12 2005[17] N Mukherjee M Paulose O K Varghese G K Mor and
C A Grimes ldquoFabrication of nanoporous tungsten oxide bygalvanostatic anodizationrdquo Journal ofMaterials Research vol 18no 10 pp 2296ndash2299 2003
[18] G B Stefanovich A L Pergament A A Velichko and L AStefanovich ldquoAnodic oxidation of vanadium and properties ofvanadium oxide filmsrdquo Journal of Physics Condensed Mattervol 16 no 23 pp 4013ndash4024 2004
[19] N K Shrestha Y-C Nah H Tsuchiya and P SchmukildquoSelf-organized nano-tubes of TiO
2-MoO
3with enhanced elec-
trochromic propertiesrdquo Chemical Communications no 15 pp2008ndash2010 2009
[20] I Paramasivam Y-C Nah C Das N K Shrestha and PSchmuki ldquoWO
3TiO2nanotubes with strongly enhanced pho-
tocatalytic activityrdquoChemistrymdashA European Journal vol 16 no30 pp 8993ndash8997 2010
[21] A Ghicov S Aldabergenova H Tsuchyia and P SchmukildquoTiO2-Nb2O5nanotubes with electrochemically tunable mor-
phologiesrdquo Angewandte ChemiemdashInternational Edition vol 45no 42 pp 6993ndash6996 2006
[22] Y Yang D Kim M Yang and P Schmuki ldquoVertically alignedmixed V
2O5-TiO2nanotube arrays for supercapacitor applica-
tionsrdquoChemical Communications vol 47 no 27 pp 7746ndash77482011
[23] H Jha R Hahn and P Schmuki ldquoUltrafast oxide nanotube for-mation on TiNb TiZr and TiTa alloys by rapid breakdown an-odizationrdquo Electrochimica Acta vol 55 no 28 pp 8883ndash88872010
[24] WWei S Berger N Shrestha and P Schmuki ldquoIdeal hexagonalorder formation of self-organized anodic oxide nanotubes andnanopores on a Ti-35Ta alloyrdquo Journal of the ElectrochemicalSociety vol 157 no 12 pp C409ndashC413 2010
[25] H Tsuchiya S Berger J M Macak A Ghicov and P SchmukildquoSelf-organized porous and tubular oxide layers on TiAl alloysrdquoElectrochemistry Communications vol 9 no 9 pp 2397ndash24022007
[26] R J D Tilley ldquoCorrelation between dielectric constant anddefect structure of non-stoichiometric solidsrdquo Nature vol 269no 5625 pp 229ndash231 1977
[27] J Lin N Masaaki A Tsukune and M Yamada ldquoTa2O5thin
films with exceptionally high dielectric constantrdquo Applied Phys-ics Letters vol 74 no 16 pp 2370ndash2372 1999
[28] H Segawa K Mori M Itagati K Sakurki and T Ishiwta ldquoIm-age sensing devicerdquo US patent no 4499384 1985
[29] C C Chen D Fang and Z Luo ldquoFabrication and characteriza-tion of highly-ordered valve-metal oxide nanotubes and theirderivative nanostructuresrdquo Reviews in Nanoscience and Nan-otechnology vol 1 no 4 pp 1ndash28 2012
[30] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions NACE Houston Tex USA 1974
[31] C W Lai and S Sreekantan ldquoEffect of applied potential onthe formation of self-organized TiO
2nanotube arrays and its
photoelectrochemical responserdquo Journal of Nanomaterials vol2011 Article ID 142463 7 pages 2011
[32] J H Lim and J Choi ldquoTitanium oxide nanowires originat-ing from anodically grown nanotubes the bamboo-splittingmodelrdquo Small vol 3 no 9 pp 1504ndash1507 2007
[33] J Tao J Zhao X Wang Y Kang and Y Li ldquoFabrication oftitania nanotube arrays on curved surfacerdquo ElectrochemistryCommunications vol 10 no 8 pp 1161ndash1163 2008
[34] D Kim F Schmidt-Stein R Hahn and P Schmuki ldquoGravityassisted growth of self-organized anodic oxide nanotubes ontitaniumrdquo Electrochemistry Communications vol 10 no 7 pp1082ndash1086 2008
[35] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons Singapore 1980
[36] G Wang Z Y Liu J N Wu and Q Lu ldquoPreparation and elec-trochemical capacitance behavior of TiO
2-B nanotubes for hy-
brid supercapacitorrdquoMaterials Letters vol 71 pp 120ndash122 2012[37] L Zhang Y Shi S Peng J Liang Z Tao and J Chen ldquoDye-
sensitized solar cells made from BaTiO3-coated TiO
2nano-
porous electrodesrdquo Journal of Photochemistry and PhotobiologyA vol 197 no 2-3 pp 260ndash265 2008
[38] XWei ldquoHydrothermal synthesis of BaTiO3thin films on nano-
porous TiO2covered Ti substratesrdquo Journal of Crystal Growth
vol 286 no 2 pp 371ndash375 2006[39] C-C Chen H-W Chung C-H Chen et al ldquoFabrication and
characterization of anodic titanium oxide nanotube arrays ofcontrolled length for highly efficient dye-sensitized solar cellsrdquoJournal of Physical Chemistry C vol 112 no 48 pp 19151ndash191572008
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
6 Journal of Nanomaterials
125 120583m
(a)
05 120583m
(b)
1120583m
(c)
125 120583m
(d)
Figure 5 SEM images of TiO2-MoO
3nanotubes film by anodizing Ti-10Mo alloy (a) a porous film and a net film on theNT top (b) a cleaned
NT top (c) small pores on the NT bottom and (d) a barrier layer on the NT bottom
Table 1 EDS results of Ti alloys oxide nanotubes
TiO2 () Ta2O5 () MoO3 ()Ti-20Ta 839 161 0Ti-10Ta 913 87 0Ti-10Mo 928 0 72
top (Figure 7(a)) smaller closed pores and a barrier layerin a hexagonal pattern are on the bottom side (Figure 7(b))tube inner surface area (Figure 7(c)) and outer surfacearea (Figure 7(d)) Denoting 119877
1and 119877
2 and 119879
1and 119879
2are
the radius and pores width of the top and bottom poresrespective119882 is the thickness of the outer barrier layer and119867 and 119871 is the inner height and total length of the nanotubeWe have 119877
1+ 1198791= 1198772+ 1198792= 1198773 and total length of nanotube
is 119871 = 119867+119882 Thus the volume of a single alloy oxide can becalculated by119881 = 119881outer minus119881inner where119881outer and119881inner can beobtained by
119881outer = 1205871198772
3times 119871
119881inner =1
3
120587 times
119867
119877
1minus 119877
2
times (119877
3
1minus 119877
3
2)
(25)
Based on the SEM images in Figures 3 4 and 5119877111987721198773
and 119882 were 60 nm 25 nm 80 nm and 40 nm respectivelyFor two hours anodization process 20120583m length of Ti alloyoxide nanotubes (119871) could be formed on the Ti alloy surfaceThus 119881outer was 04120583m
3 and 119881inner was 012 120583m3 and the
volume of a single alloy oxide nanotube (119881) was 028120583m3The TiO
2nanotubes density has been recently reported by
Chen et al [29] such that there are 4510548978 nanotubesper cm2 Therefore the total volume of Ti alloy nanotubeswas 126 times 10minus3 cm3 in 1 cm2 sample area Moreover it hasalso been reported that nanotube surface area is greatlyincreased when 119871 = 10 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 and 119871 = 100 120583m 119878inner = 1205 cm
2 119878outer =2402 cm2 Figure 8 furthermore accumulated anodic Ti andTi alloy NT inner and outer surface areas increased withfilm thickness increased based on 1 cm2 substrate Hence theextremely high surface area is able to provide more chancesfor electrochemical reactions
According to the Pourbaix diagrams in Figure 2 anodiz-ing Ti Ti-20Ta Ti-10Ta and Ti-10Mo can form anodic oxidefilms of these Ti alloys Therefore the following alloy anodicoxide films densities are able to be calculated based on theTiO2 Ta2O5 andMoO
3densities of 42 gcm3 82 gcm3 and
Journal of Nanomaterials 7
Table 2 Specific capacitance based on TiO2 NT Ti-10Ta NT Ti-20Ta NT and Ti-10Mo NT films
Sample size (1 cm2times 20 120583m) TiO2 NT Ti-10Ta NT Ti-20Ta NT Ti-10Mo NT
Density (gcm2) 309 319 365 307Mass of unit area (mgcm2) 618 638 730 614119889119876 (mC) 6558 12002 14330 10292119889119864 (V) 09 09 09 09Specific capacitance (Fg) 118 209 218 186
(a)
(b)
(c)
(d)
Ti-Ta or Ti-Mo alloy
Barrier layer
TiO2-Ta2O5NT or TiO2-MoO3 NT
(e)
Figure 6The schematic diagram of TiO2-Ta2O5NT or TiO
2-MoO
3
NT film structure (a) compact layer (b) partial porous film (c)porous film (d) net film and (e) TiO
2-Ta2O5NT or TiO
2-MoO
3
NT and barrier layer on the Ti-Ta or Ti-Mo alloy
47 gcm3 respectively According to EDS results in Table 1Ti Ti-20Ta Ti-10Ta and Ti-10Mo formed 100 TiO
2 839
TiO2+ 161 Ta
2O5 913 TiO
2+ 87 Ta
2O5 and 928
TiO2+ 72MoO
3The densities of 100TiO
2 839TiO
2+
161 Ta2O5 913 TiO
2+ 87 Ta
2O5 and 928 TiO
2+
72 MoO3were 423 gcm3 484 gcm3 454 gcm3 and
424 gcm3 respectively Therefore the mass of nanotubesfilms 1 cm2 sample for each alloy was listed in Table 2 being532mgcm2 609mgcm2 572mgcm2 and 534mgcm2
Cyclic voltammograms (CV) are used to characterize thecapacitors behavior of the alloy oxide nanotubes Figure 9shows capacitance performance evaluations for the Ti alloyanodic oxide nanotubes by cyclic voltammograms It is clearthat Ti alloy oxide nanotubes had larger area of CV curvethan pure TiO
2nanotube did It means that Ti alloys oxide
nanotubes had larger capacitances than pure TiO2nanotubes
Besides more Ta2O5content can significantly enhance the
capacitor performance by comparing two Ti-Ta alloys curveswith different compositions Moreover Ti-10Mo alloy oxidenanotubes CV curve shows a symmetrical shape whichindicates that the revisable redox reaction of Mo2+Mo3+ washelpful to improve the capacitor performance The specificcapacitance (119862) can bemeasured by voltage step current stepor voltage ramp methods and evaluated by the equations of119862 = 119876119881 and 119862 = 119889119876119889119881 [35] where 119881 is applied voltageand 119876 is the quantity of charge on the electrode (whichcan be evaluated from the area of the CV curve) Table 2shows the specific capacitance based on 1 cm2 sample areaand 20120583m film thickness of pure Ti Ti-20Ta Ti-10Ta andTi-10Mo oxide nanotubes films which are 137 Fg 261 Fg233 Fg and 214 Fg respectively The specific capacitancesof Ti alloys oxide nanotubes films were higher than thatof TiO
2-B nanowiresMWCNTs hybrid supercapacitor with
specific capacitance of 177 Fg [36]
4 Conclusions
In summary we fabricated ultracapacitors based on thework-ing electrode made of highly ordered anodic TiO
2 Ta2O5
and MoO3nanotubes directly formed on pure Ti Ti-20Ta
Ti-10Ta and Ti-10Mo substrates The ordered alloys oxidenanotubes structure has a volume of 126 times 10minus3 cm3 in 1 cm2sample area with nanotube density of 45 times 109 tubescm2The mass of pure Ti and Ti alloys oxide nanotubes films with1 cm2 sample size and 20120583m film thickness can be calcu-lated as 532mg (TiO
2nanotubes) 609mg (Ti-20Ta oxide
nanotubes) 572mg (Ti-10Ta oxide nanotubes) and 534mg
8 Journal of Nanomaterials
H
W
R1
R2
R3
(a)
Top
Bottom
R1
R2
T1
T2
(b)
L
Inne
r sur
face
2120587R1
2120587R2
(c)
Out
er su
rface
H+W
4radic3(R1 + T1)
(d)
Figure 7 Estimation of TiO2NT surface (a) cone structure of inner
tube with radius of 1198773 and 119877
1 and 119877
2on the tube top and bottom
tube length with 119867 (b) pore wall thickness with 1198791and 119879
2on the
tube top and bottom (c) tube inner surface area and (d) outersurface area
0
500
1000
1500
2000
2500
0 25 50 75 100
Outer surface area
Inner surface area
Length (120583m)
Surfa
ce ar
ea (c
m2)
Figure 8 Accumulated anodic Ti and Ti alloy NT inner and outersurface areas based on 1 cm2 substrate
0
2
4
01SEC (V)
minus11minus6
minus4
minus2
minus08 minus05 minus02
Curr
ent d
ensit
y (m
Ac
m2)
TiO2
Ti-10MoO3
TiO2-10Ta2O5TiO2-20Ta2O5
Figure 9 Capacitance performance evaluations for TiO2NT TiO
2-
10 Ta2O5NT TiO
2-20 Ta
2O5NT and TiO
2-10 MoO
3NT by cyclic
voltammograms
(Ti-10Mo oxide nanotubes) respectively Furthermore Tialloy anodic oxide nanotubes films with 1 cm2 surface and20120583m thickness have an inner surface area of 2410 cm2 andouter surface area of 4804 cm2 Thus such large surface areaof dielectric oxides caused very high specific capacitancesThe specific capacitance can further be enhanced by (1)reacting with barium nitrate (Ba(NO
3)2) [37] or barium
hydroxide (Ba(OH)2) [38] to form a very high dielectric
constant BaTiO3film (2) increasing nanotubes length by
longer anodization process and (3) increasing nanotubessurface area by coating TiO
2nanoparticles on the nanotubes
surface [39]
Acknowledgment
This study was partially supported by a Grant from theNational Science Council Taiwan (102-3113-P-042A-005-)
References
[1] L E Cross ldquoFerroelectric materials for electromechanicaltransducer applicationsrdquo Materials Chemistry and Physics vol43 no 2 pp 108ndash115 1996
[2] A D Hilton and R Frost ldquoRecent developments in the manu-facture of barium titanate powdersrdquo Key Engineering Materialsvol 66 pp 145ndash184 1992
[3] L E Cross ldquoDielectric piezoelectric and ferroelectric compo-nentsrdquo American Ceramic Society Bulletin vol 63 no 4 pp586ndash590 1984
[4] D Pandey A P Singh and V S Tiwari ldquoDevelopments inferroelectric ceramics for capacitor applicationsrdquo Bulletin ofMaterials Science vol 15 no 5 pp 391ndash402 1992
[5] K Kajiyoshi N Ishizawa and M Yoshimura ldquoPreparation oftetragonal barium titanate thin film on titaniummetal substrateby hydrothermal methodrdquo Journal of the American CeramicSociety vol 74 no 2 pp 369ndash374 1991
[6] T Horikawa N Mikami T Makita et al ldquoDielectric propertiesof (Ba Sr)TiO
3thin films deposited by RF sputteringrdquo Japanese
Journal of Applied Physics vol 32 no 9 pp 4126ndash4130 1993
Journal of Nanomaterials 9
[7] A S Shaikh and G M Vest ldquoKinetics of BaTiO3and PbTiO
3
formation from metallo-organic precursorsrdquo Journal of theAmerican Ceramic Society vol 69 no 9 pp 682ndash688 1986
[8] H Okamura andH K Bowen ldquoPreparation of alkoxides for thesynthesis of ceramicsrdquo Ceramics International vol 12 no 3 pp161ndash171 1986
[9] K W Kirby ldquoAlkoxide synthesis techniques for BaTiO3rdquoMate-
rials Research Bulletin vol 23 no 6 pp 881ndash890 1988[10] P Bhattacharya T Komeda K-H Park and Y Nishioka
ldquoComparative study of amorphous and crystalline (Ba Sr)TiO3
thin films deposited by laser ablationrdquo Japanese Journal ofApplied Physics vol 32 no 9 pp 4103ndash4106 1993
[11] D M Tahan A Safari and L C Klein ldquoPreparation and char-acterization of Ba
119909Sr1minus119909
TiO3thin films by a Sol-Gel techniquerdquo
Journal of the American Ceramic Society vol 79 no 6 pp 1593ndash1598 1996
[12] C-C Chen J-H Chen C-G Chao and W C Say ldquoElectro-chemical characteristics of surface of titanium formed by elec-trolytic polishing and anodizingrdquo Journal of Materials Sciencevol 40 no 15 pp 4053ndash4059 2005
[13] C-C Chen Y Bisrat Z P Luo R E Schaak C-G Chao andD C Lagoudas ldquoFabrication of single-crystal tin nanowires byhydraulic pressure injectionrdquo Nanotechnology vol 17 no 2 pp367ndash374 2006
[14] H Tsuchiya and P Schmuki ldquoSelf-organized high aspect ratioporous hafnium oxide prepared by electrochemical anodiza-tionrdquo Electrochemistry Communications vol 7 no 1 pp 49ndash522005
[15] I Sieber H Hildebrand A Friedrich and P Schmuki ldquoForma-tion of self-organized niobium porous oxide on niobiumrdquo Elec-trochemistry Communications vol 7 no 1 pp 97ndash100 2005
[16] I Sieber B Kannan and P Schmuki ldquoSelf-assembled poroustantalum oxide prepared in H
2SO4HF electrolytesrdquo Electro-
chemical and Solid-State Letters vol 8 no 3 pp J10ndashJ12 2005[17] N Mukherjee M Paulose O K Varghese G K Mor and
C A Grimes ldquoFabrication of nanoporous tungsten oxide bygalvanostatic anodizationrdquo Journal ofMaterials Research vol 18no 10 pp 2296ndash2299 2003
[18] G B Stefanovich A L Pergament A A Velichko and L AStefanovich ldquoAnodic oxidation of vanadium and properties ofvanadium oxide filmsrdquo Journal of Physics Condensed Mattervol 16 no 23 pp 4013ndash4024 2004
[19] N K Shrestha Y-C Nah H Tsuchiya and P SchmukildquoSelf-organized nano-tubes of TiO
2-MoO
3with enhanced elec-
trochromic propertiesrdquo Chemical Communications no 15 pp2008ndash2010 2009
[20] I Paramasivam Y-C Nah C Das N K Shrestha and PSchmuki ldquoWO
3TiO2nanotubes with strongly enhanced pho-
tocatalytic activityrdquoChemistrymdashA European Journal vol 16 no30 pp 8993ndash8997 2010
[21] A Ghicov S Aldabergenova H Tsuchyia and P SchmukildquoTiO2-Nb2O5nanotubes with electrochemically tunable mor-
phologiesrdquo Angewandte ChemiemdashInternational Edition vol 45no 42 pp 6993ndash6996 2006
[22] Y Yang D Kim M Yang and P Schmuki ldquoVertically alignedmixed V
2O5-TiO2nanotube arrays for supercapacitor applica-
tionsrdquoChemical Communications vol 47 no 27 pp 7746ndash77482011
[23] H Jha R Hahn and P Schmuki ldquoUltrafast oxide nanotube for-mation on TiNb TiZr and TiTa alloys by rapid breakdown an-odizationrdquo Electrochimica Acta vol 55 no 28 pp 8883ndash88872010
[24] WWei S Berger N Shrestha and P Schmuki ldquoIdeal hexagonalorder formation of self-organized anodic oxide nanotubes andnanopores on a Ti-35Ta alloyrdquo Journal of the ElectrochemicalSociety vol 157 no 12 pp C409ndashC413 2010
[25] H Tsuchiya S Berger J M Macak A Ghicov and P SchmukildquoSelf-organized porous and tubular oxide layers on TiAl alloysrdquoElectrochemistry Communications vol 9 no 9 pp 2397ndash24022007
[26] R J D Tilley ldquoCorrelation between dielectric constant anddefect structure of non-stoichiometric solidsrdquo Nature vol 269no 5625 pp 229ndash231 1977
[27] J Lin N Masaaki A Tsukune and M Yamada ldquoTa2O5thin
films with exceptionally high dielectric constantrdquo Applied Phys-ics Letters vol 74 no 16 pp 2370ndash2372 1999
[28] H Segawa K Mori M Itagati K Sakurki and T Ishiwta ldquoIm-age sensing devicerdquo US patent no 4499384 1985
[29] C C Chen D Fang and Z Luo ldquoFabrication and characteriza-tion of highly-ordered valve-metal oxide nanotubes and theirderivative nanostructuresrdquo Reviews in Nanoscience and Nan-otechnology vol 1 no 4 pp 1ndash28 2012
[30] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions NACE Houston Tex USA 1974
[31] C W Lai and S Sreekantan ldquoEffect of applied potential onthe formation of self-organized TiO
2nanotube arrays and its
photoelectrochemical responserdquo Journal of Nanomaterials vol2011 Article ID 142463 7 pages 2011
[32] J H Lim and J Choi ldquoTitanium oxide nanowires originat-ing from anodically grown nanotubes the bamboo-splittingmodelrdquo Small vol 3 no 9 pp 1504ndash1507 2007
[33] J Tao J Zhao X Wang Y Kang and Y Li ldquoFabrication oftitania nanotube arrays on curved surfacerdquo ElectrochemistryCommunications vol 10 no 8 pp 1161ndash1163 2008
[34] D Kim F Schmidt-Stein R Hahn and P Schmuki ldquoGravityassisted growth of self-organized anodic oxide nanotubes ontitaniumrdquo Electrochemistry Communications vol 10 no 7 pp1082ndash1086 2008
[35] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons Singapore 1980
[36] G Wang Z Y Liu J N Wu and Q Lu ldquoPreparation and elec-trochemical capacitance behavior of TiO
2-B nanotubes for hy-
brid supercapacitorrdquoMaterials Letters vol 71 pp 120ndash122 2012[37] L Zhang Y Shi S Peng J Liang Z Tao and J Chen ldquoDye-
sensitized solar cells made from BaTiO3-coated TiO
2nano-
porous electrodesrdquo Journal of Photochemistry and PhotobiologyA vol 197 no 2-3 pp 260ndash265 2008
[38] XWei ldquoHydrothermal synthesis of BaTiO3thin films on nano-
porous TiO2covered Ti substratesrdquo Journal of Crystal Growth
vol 286 no 2 pp 371ndash375 2006[39] C-C Chen H-W Chung C-H Chen et al ldquoFabrication and
characterization of anodic titanium oxide nanotube arrays ofcontrolled length for highly efficient dye-sensitized solar cellsrdquoJournal of Physical Chemistry C vol 112 no 48 pp 19151ndash191572008
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Journal of Nanomaterials 7
Table 2 Specific capacitance based on TiO2 NT Ti-10Ta NT Ti-20Ta NT and Ti-10Mo NT films
Sample size (1 cm2times 20 120583m) TiO2 NT Ti-10Ta NT Ti-20Ta NT Ti-10Mo NT
Density (gcm2) 309 319 365 307Mass of unit area (mgcm2) 618 638 730 614119889119876 (mC) 6558 12002 14330 10292119889119864 (V) 09 09 09 09Specific capacitance (Fg) 118 209 218 186
(a)
(b)
(c)
(d)
Ti-Ta or Ti-Mo alloy
Barrier layer
TiO2-Ta2O5NT or TiO2-MoO3 NT
(e)
Figure 6The schematic diagram of TiO2-Ta2O5NT or TiO
2-MoO
3
NT film structure (a) compact layer (b) partial porous film (c)porous film (d) net film and (e) TiO
2-Ta2O5NT or TiO
2-MoO
3
NT and barrier layer on the Ti-Ta or Ti-Mo alloy
47 gcm3 respectively According to EDS results in Table 1Ti Ti-20Ta Ti-10Ta and Ti-10Mo formed 100 TiO
2 839
TiO2+ 161 Ta
2O5 913 TiO
2+ 87 Ta
2O5 and 928
TiO2+ 72MoO
3The densities of 100TiO
2 839TiO
2+
161 Ta2O5 913 TiO
2+ 87 Ta
2O5 and 928 TiO
2+
72 MoO3were 423 gcm3 484 gcm3 454 gcm3 and
424 gcm3 respectively Therefore the mass of nanotubesfilms 1 cm2 sample for each alloy was listed in Table 2 being532mgcm2 609mgcm2 572mgcm2 and 534mgcm2
Cyclic voltammograms (CV) are used to characterize thecapacitors behavior of the alloy oxide nanotubes Figure 9shows capacitance performance evaluations for the Ti alloyanodic oxide nanotubes by cyclic voltammograms It is clearthat Ti alloy oxide nanotubes had larger area of CV curvethan pure TiO
2nanotube did It means that Ti alloys oxide
nanotubes had larger capacitances than pure TiO2nanotubes
Besides more Ta2O5content can significantly enhance the
capacitor performance by comparing two Ti-Ta alloys curveswith different compositions Moreover Ti-10Mo alloy oxidenanotubes CV curve shows a symmetrical shape whichindicates that the revisable redox reaction of Mo2+Mo3+ washelpful to improve the capacitor performance The specificcapacitance (119862) can bemeasured by voltage step current stepor voltage ramp methods and evaluated by the equations of119862 = 119876119881 and 119862 = 119889119876119889119881 [35] where 119881 is applied voltageand 119876 is the quantity of charge on the electrode (whichcan be evaluated from the area of the CV curve) Table 2shows the specific capacitance based on 1 cm2 sample areaand 20120583m film thickness of pure Ti Ti-20Ta Ti-10Ta andTi-10Mo oxide nanotubes films which are 137 Fg 261 Fg233 Fg and 214 Fg respectively The specific capacitancesof Ti alloys oxide nanotubes films were higher than thatof TiO
2-B nanowiresMWCNTs hybrid supercapacitor with
specific capacitance of 177 Fg [36]
4 Conclusions
In summary we fabricated ultracapacitors based on thework-ing electrode made of highly ordered anodic TiO
2 Ta2O5
and MoO3nanotubes directly formed on pure Ti Ti-20Ta
Ti-10Ta and Ti-10Mo substrates The ordered alloys oxidenanotubes structure has a volume of 126 times 10minus3 cm3 in 1 cm2sample area with nanotube density of 45 times 109 tubescm2The mass of pure Ti and Ti alloys oxide nanotubes films with1 cm2 sample size and 20120583m film thickness can be calcu-lated as 532mg (TiO
2nanotubes) 609mg (Ti-20Ta oxide
nanotubes) 572mg (Ti-10Ta oxide nanotubes) and 534mg
8 Journal of Nanomaterials
H
W
R1
R2
R3
(a)
Top
Bottom
R1
R2
T1
T2
(b)
L
Inne
r sur
face
2120587R1
2120587R2
(c)
Out
er su
rface
H+W
4radic3(R1 + T1)
(d)
Figure 7 Estimation of TiO2NT surface (a) cone structure of inner
tube with radius of 1198773 and 119877
1 and 119877
2on the tube top and bottom
tube length with 119867 (b) pore wall thickness with 1198791and 119879
2on the
tube top and bottom (c) tube inner surface area and (d) outersurface area
0
500
1000
1500
2000
2500
0 25 50 75 100
Outer surface area
Inner surface area
Length (120583m)
Surfa
ce ar
ea (c
m2)
Figure 8 Accumulated anodic Ti and Ti alloy NT inner and outersurface areas based on 1 cm2 substrate
0
2
4
01SEC (V)
minus11minus6
minus4
minus2
minus08 minus05 minus02
Curr
ent d
ensit
y (m
Ac
m2)
TiO2
Ti-10MoO3
TiO2-10Ta2O5TiO2-20Ta2O5
Figure 9 Capacitance performance evaluations for TiO2NT TiO
2-
10 Ta2O5NT TiO
2-20 Ta
2O5NT and TiO
2-10 MoO
3NT by cyclic
voltammograms
(Ti-10Mo oxide nanotubes) respectively Furthermore Tialloy anodic oxide nanotubes films with 1 cm2 surface and20120583m thickness have an inner surface area of 2410 cm2 andouter surface area of 4804 cm2 Thus such large surface areaof dielectric oxides caused very high specific capacitancesThe specific capacitance can further be enhanced by (1)reacting with barium nitrate (Ba(NO
3)2) [37] or barium
hydroxide (Ba(OH)2) [38] to form a very high dielectric
constant BaTiO3film (2) increasing nanotubes length by
longer anodization process and (3) increasing nanotubessurface area by coating TiO
2nanoparticles on the nanotubes
surface [39]
Acknowledgment
This study was partially supported by a Grant from theNational Science Council Taiwan (102-3113-P-042A-005-)
References
[1] L E Cross ldquoFerroelectric materials for electromechanicaltransducer applicationsrdquo Materials Chemistry and Physics vol43 no 2 pp 108ndash115 1996
[2] A D Hilton and R Frost ldquoRecent developments in the manu-facture of barium titanate powdersrdquo Key Engineering Materialsvol 66 pp 145ndash184 1992
[3] L E Cross ldquoDielectric piezoelectric and ferroelectric compo-nentsrdquo American Ceramic Society Bulletin vol 63 no 4 pp586ndash590 1984
[4] D Pandey A P Singh and V S Tiwari ldquoDevelopments inferroelectric ceramics for capacitor applicationsrdquo Bulletin ofMaterials Science vol 15 no 5 pp 391ndash402 1992
[5] K Kajiyoshi N Ishizawa and M Yoshimura ldquoPreparation oftetragonal barium titanate thin film on titaniummetal substrateby hydrothermal methodrdquo Journal of the American CeramicSociety vol 74 no 2 pp 369ndash374 1991
[6] T Horikawa N Mikami T Makita et al ldquoDielectric propertiesof (Ba Sr)TiO
3thin films deposited by RF sputteringrdquo Japanese
Journal of Applied Physics vol 32 no 9 pp 4126ndash4130 1993
Journal of Nanomaterials 9
[7] A S Shaikh and G M Vest ldquoKinetics of BaTiO3and PbTiO
3
formation from metallo-organic precursorsrdquo Journal of theAmerican Ceramic Society vol 69 no 9 pp 682ndash688 1986
[8] H Okamura andH K Bowen ldquoPreparation of alkoxides for thesynthesis of ceramicsrdquo Ceramics International vol 12 no 3 pp161ndash171 1986
[9] K W Kirby ldquoAlkoxide synthesis techniques for BaTiO3rdquoMate-
rials Research Bulletin vol 23 no 6 pp 881ndash890 1988[10] P Bhattacharya T Komeda K-H Park and Y Nishioka
ldquoComparative study of amorphous and crystalline (Ba Sr)TiO3
thin films deposited by laser ablationrdquo Japanese Journal ofApplied Physics vol 32 no 9 pp 4103ndash4106 1993
[11] D M Tahan A Safari and L C Klein ldquoPreparation and char-acterization of Ba
119909Sr1minus119909
TiO3thin films by a Sol-Gel techniquerdquo
Journal of the American Ceramic Society vol 79 no 6 pp 1593ndash1598 1996
[12] C-C Chen J-H Chen C-G Chao and W C Say ldquoElectro-chemical characteristics of surface of titanium formed by elec-trolytic polishing and anodizingrdquo Journal of Materials Sciencevol 40 no 15 pp 4053ndash4059 2005
[13] C-C Chen Y Bisrat Z P Luo R E Schaak C-G Chao andD C Lagoudas ldquoFabrication of single-crystal tin nanowires byhydraulic pressure injectionrdquo Nanotechnology vol 17 no 2 pp367ndash374 2006
[14] H Tsuchiya and P Schmuki ldquoSelf-organized high aspect ratioporous hafnium oxide prepared by electrochemical anodiza-tionrdquo Electrochemistry Communications vol 7 no 1 pp 49ndash522005
[15] I Sieber H Hildebrand A Friedrich and P Schmuki ldquoForma-tion of self-organized niobium porous oxide on niobiumrdquo Elec-trochemistry Communications vol 7 no 1 pp 97ndash100 2005
[16] I Sieber B Kannan and P Schmuki ldquoSelf-assembled poroustantalum oxide prepared in H
2SO4HF electrolytesrdquo Electro-
chemical and Solid-State Letters vol 8 no 3 pp J10ndashJ12 2005[17] N Mukherjee M Paulose O K Varghese G K Mor and
C A Grimes ldquoFabrication of nanoporous tungsten oxide bygalvanostatic anodizationrdquo Journal ofMaterials Research vol 18no 10 pp 2296ndash2299 2003
[18] G B Stefanovich A L Pergament A A Velichko and L AStefanovich ldquoAnodic oxidation of vanadium and properties ofvanadium oxide filmsrdquo Journal of Physics Condensed Mattervol 16 no 23 pp 4013ndash4024 2004
[19] N K Shrestha Y-C Nah H Tsuchiya and P SchmukildquoSelf-organized nano-tubes of TiO
2-MoO
3with enhanced elec-
trochromic propertiesrdquo Chemical Communications no 15 pp2008ndash2010 2009
[20] I Paramasivam Y-C Nah C Das N K Shrestha and PSchmuki ldquoWO
3TiO2nanotubes with strongly enhanced pho-
tocatalytic activityrdquoChemistrymdashA European Journal vol 16 no30 pp 8993ndash8997 2010
[21] A Ghicov S Aldabergenova H Tsuchyia and P SchmukildquoTiO2-Nb2O5nanotubes with electrochemically tunable mor-
phologiesrdquo Angewandte ChemiemdashInternational Edition vol 45no 42 pp 6993ndash6996 2006
[22] Y Yang D Kim M Yang and P Schmuki ldquoVertically alignedmixed V
2O5-TiO2nanotube arrays for supercapacitor applica-
tionsrdquoChemical Communications vol 47 no 27 pp 7746ndash77482011
[23] H Jha R Hahn and P Schmuki ldquoUltrafast oxide nanotube for-mation on TiNb TiZr and TiTa alloys by rapid breakdown an-odizationrdquo Electrochimica Acta vol 55 no 28 pp 8883ndash88872010
[24] WWei S Berger N Shrestha and P Schmuki ldquoIdeal hexagonalorder formation of self-organized anodic oxide nanotubes andnanopores on a Ti-35Ta alloyrdquo Journal of the ElectrochemicalSociety vol 157 no 12 pp C409ndashC413 2010
[25] H Tsuchiya S Berger J M Macak A Ghicov and P SchmukildquoSelf-organized porous and tubular oxide layers on TiAl alloysrdquoElectrochemistry Communications vol 9 no 9 pp 2397ndash24022007
[26] R J D Tilley ldquoCorrelation between dielectric constant anddefect structure of non-stoichiometric solidsrdquo Nature vol 269no 5625 pp 229ndash231 1977
[27] J Lin N Masaaki A Tsukune and M Yamada ldquoTa2O5thin
films with exceptionally high dielectric constantrdquo Applied Phys-ics Letters vol 74 no 16 pp 2370ndash2372 1999
[28] H Segawa K Mori M Itagati K Sakurki and T Ishiwta ldquoIm-age sensing devicerdquo US patent no 4499384 1985
[29] C C Chen D Fang and Z Luo ldquoFabrication and characteriza-tion of highly-ordered valve-metal oxide nanotubes and theirderivative nanostructuresrdquo Reviews in Nanoscience and Nan-otechnology vol 1 no 4 pp 1ndash28 2012
[30] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions NACE Houston Tex USA 1974
[31] C W Lai and S Sreekantan ldquoEffect of applied potential onthe formation of self-organized TiO
2nanotube arrays and its
photoelectrochemical responserdquo Journal of Nanomaterials vol2011 Article ID 142463 7 pages 2011
[32] J H Lim and J Choi ldquoTitanium oxide nanowires originat-ing from anodically grown nanotubes the bamboo-splittingmodelrdquo Small vol 3 no 9 pp 1504ndash1507 2007
[33] J Tao J Zhao X Wang Y Kang and Y Li ldquoFabrication oftitania nanotube arrays on curved surfacerdquo ElectrochemistryCommunications vol 10 no 8 pp 1161ndash1163 2008
[34] D Kim F Schmidt-Stein R Hahn and P Schmuki ldquoGravityassisted growth of self-organized anodic oxide nanotubes ontitaniumrdquo Electrochemistry Communications vol 10 no 7 pp1082ndash1086 2008
[35] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons Singapore 1980
[36] G Wang Z Y Liu J N Wu and Q Lu ldquoPreparation and elec-trochemical capacitance behavior of TiO
2-B nanotubes for hy-
brid supercapacitorrdquoMaterials Letters vol 71 pp 120ndash122 2012[37] L Zhang Y Shi S Peng J Liang Z Tao and J Chen ldquoDye-
sensitized solar cells made from BaTiO3-coated TiO
2nano-
porous electrodesrdquo Journal of Photochemistry and PhotobiologyA vol 197 no 2-3 pp 260ndash265 2008
[38] XWei ldquoHydrothermal synthesis of BaTiO3thin films on nano-
porous TiO2covered Ti substratesrdquo Journal of Crystal Growth
vol 286 no 2 pp 371ndash375 2006[39] C-C Chen H-W Chung C-H Chen et al ldquoFabrication and
characterization of anodic titanium oxide nanotube arrays ofcontrolled length for highly efficient dye-sensitized solar cellsrdquoJournal of Physical Chemistry C vol 112 no 48 pp 19151ndash191572008
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
8 Journal of Nanomaterials
H
W
R1
R2
R3
(a)
Top
Bottom
R1
R2
T1
T2
(b)
L
Inne
r sur
face
2120587R1
2120587R2
(c)
Out
er su
rface
H+W
4radic3(R1 + T1)
(d)
Figure 7 Estimation of TiO2NT surface (a) cone structure of inner
tube with radius of 1198773 and 119877
1 and 119877
2on the tube top and bottom
tube length with 119867 (b) pore wall thickness with 1198791and 119879
2on the
tube top and bottom (c) tube inner surface area and (d) outersurface area
0
500
1000
1500
2000
2500
0 25 50 75 100
Outer surface area
Inner surface area
Length (120583m)
Surfa
ce ar
ea (c
m2)
Figure 8 Accumulated anodic Ti and Ti alloy NT inner and outersurface areas based on 1 cm2 substrate
0
2
4
01SEC (V)
minus11minus6
minus4
minus2
minus08 minus05 minus02
Curr
ent d
ensit
y (m
Ac
m2)
TiO2
Ti-10MoO3
TiO2-10Ta2O5TiO2-20Ta2O5
Figure 9 Capacitance performance evaluations for TiO2NT TiO
2-
10 Ta2O5NT TiO
2-20 Ta
2O5NT and TiO
2-10 MoO
3NT by cyclic
voltammograms
(Ti-10Mo oxide nanotubes) respectively Furthermore Tialloy anodic oxide nanotubes films with 1 cm2 surface and20120583m thickness have an inner surface area of 2410 cm2 andouter surface area of 4804 cm2 Thus such large surface areaof dielectric oxides caused very high specific capacitancesThe specific capacitance can further be enhanced by (1)reacting with barium nitrate (Ba(NO
3)2) [37] or barium
hydroxide (Ba(OH)2) [38] to form a very high dielectric
constant BaTiO3film (2) increasing nanotubes length by
longer anodization process and (3) increasing nanotubessurface area by coating TiO
2nanoparticles on the nanotubes
surface [39]
Acknowledgment
This study was partially supported by a Grant from theNational Science Council Taiwan (102-3113-P-042A-005-)
References
[1] L E Cross ldquoFerroelectric materials for electromechanicaltransducer applicationsrdquo Materials Chemistry and Physics vol43 no 2 pp 108ndash115 1996
[2] A D Hilton and R Frost ldquoRecent developments in the manu-facture of barium titanate powdersrdquo Key Engineering Materialsvol 66 pp 145ndash184 1992
[3] L E Cross ldquoDielectric piezoelectric and ferroelectric compo-nentsrdquo American Ceramic Society Bulletin vol 63 no 4 pp586ndash590 1984
[4] D Pandey A P Singh and V S Tiwari ldquoDevelopments inferroelectric ceramics for capacitor applicationsrdquo Bulletin ofMaterials Science vol 15 no 5 pp 391ndash402 1992
[5] K Kajiyoshi N Ishizawa and M Yoshimura ldquoPreparation oftetragonal barium titanate thin film on titaniummetal substrateby hydrothermal methodrdquo Journal of the American CeramicSociety vol 74 no 2 pp 369ndash374 1991
[6] T Horikawa N Mikami T Makita et al ldquoDielectric propertiesof (Ba Sr)TiO
3thin films deposited by RF sputteringrdquo Japanese
Journal of Applied Physics vol 32 no 9 pp 4126ndash4130 1993
Journal of Nanomaterials 9
[7] A S Shaikh and G M Vest ldquoKinetics of BaTiO3and PbTiO
3
formation from metallo-organic precursorsrdquo Journal of theAmerican Ceramic Society vol 69 no 9 pp 682ndash688 1986
[8] H Okamura andH K Bowen ldquoPreparation of alkoxides for thesynthesis of ceramicsrdquo Ceramics International vol 12 no 3 pp161ndash171 1986
[9] K W Kirby ldquoAlkoxide synthesis techniques for BaTiO3rdquoMate-
rials Research Bulletin vol 23 no 6 pp 881ndash890 1988[10] P Bhattacharya T Komeda K-H Park and Y Nishioka
ldquoComparative study of amorphous and crystalline (Ba Sr)TiO3
thin films deposited by laser ablationrdquo Japanese Journal ofApplied Physics vol 32 no 9 pp 4103ndash4106 1993
[11] D M Tahan A Safari and L C Klein ldquoPreparation and char-acterization of Ba
119909Sr1minus119909
TiO3thin films by a Sol-Gel techniquerdquo
Journal of the American Ceramic Society vol 79 no 6 pp 1593ndash1598 1996
[12] C-C Chen J-H Chen C-G Chao and W C Say ldquoElectro-chemical characteristics of surface of titanium formed by elec-trolytic polishing and anodizingrdquo Journal of Materials Sciencevol 40 no 15 pp 4053ndash4059 2005
[13] C-C Chen Y Bisrat Z P Luo R E Schaak C-G Chao andD C Lagoudas ldquoFabrication of single-crystal tin nanowires byhydraulic pressure injectionrdquo Nanotechnology vol 17 no 2 pp367ndash374 2006
[14] H Tsuchiya and P Schmuki ldquoSelf-organized high aspect ratioporous hafnium oxide prepared by electrochemical anodiza-tionrdquo Electrochemistry Communications vol 7 no 1 pp 49ndash522005
[15] I Sieber H Hildebrand A Friedrich and P Schmuki ldquoForma-tion of self-organized niobium porous oxide on niobiumrdquo Elec-trochemistry Communications vol 7 no 1 pp 97ndash100 2005
[16] I Sieber B Kannan and P Schmuki ldquoSelf-assembled poroustantalum oxide prepared in H
2SO4HF electrolytesrdquo Electro-
chemical and Solid-State Letters vol 8 no 3 pp J10ndashJ12 2005[17] N Mukherjee M Paulose O K Varghese G K Mor and
C A Grimes ldquoFabrication of nanoporous tungsten oxide bygalvanostatic anodizationrdquo Journal ofMaterials Research vol 18no 10 pp 2296ndash2299 2003
[18] G B Stefanovich A L Pergament A A Velichko and L AStefanovich ldquoAnodic oxidation of vanadium and properties ofvanadium oxide filmsrdquo Journal of Physics Condensed Mattervol 16 no 23 pp 4013ndash4024 2004
[19] N K Shrestha Y-C Nah H Tsuchiya and P SchmukildquoSelf-organized nano-tubes of TiO
2-MoO
3with enhanced elec-
trochromic propertiesrdquo Chemical Communications no 15 pp2008ndash2010 2009
[20] I Paramasivam Y-C Nah C Das N K Shrestha and PSchmuki ldquoWO
3TiO2nanotubes with strongly enhanced pho-
tocatalytic activityrdquoChemistrymdashA European Journal vol 16 no30 pp 8993ndash8997 2010
[21] A Ghicov S Aldabergenova H Tsuchyia and P SchmukildquoTiO2-Nb2O5nanotubes with electrochemically tunable mor-
phologiesrdquo Angewandte ChemiemdashInternational Edition vol 45no 42 pp 6993ndash6996 2006
[22] Y Yang D Kim M Yang and P Schmuki ldquoVertically alignedmixed V
2O5-TiO2nanotube arrays for supercapacitor applica-
tionsrdquoChemical Communications vol 47 no 27 pp 7746ndash77482011
[23] H Jha R Hahn and P Schmuki ldquoUltrafast oxide nanotube for-mation on TiNb TiZr and TiTa alloys by rapid breakdown an-odizationrdquo Electrochimica Acta vol 55 no 28 pp 8883ndash88872010
[24] WWei S Berger N Shrestha and P Schmuki ldquoIdeal hexagonalorder formation of self-organized anodic oxide nanotubes andnanopores on a Ti-35Ta alloyrdquo Journal of the ElectrochemicalSociety vol 157 no 12 pp C409ndashC413 2010
[25] H Tsuchiya S Berger J M Macak A Ghicov and P SchmukildquoSelf-organized porous and tubular oxide layers on TiAl alloysrdquoElectrochemistry Communications vol 9 no 9 pp 2397ndash24022007
[26] R J D Tilley ldquoCorrelation between dielectric constant anddefect structure of non-stoichiometric solidsrdquo Nature vol 269no 5625 pp 229ndash231 1977
[27] J Lin N Masaaki A Tsukune and M Yamada ldquoTa2O5thin
films with exceptionally high dielectric constantrdquo Applied Phys-ics Letters vol 74 no 16 pp 2370ndash2372 1999
[28] H Segawa K Mori M Itagati K Sakurki and T Ishiwta ldquoIm-age sensing devicerdquo US patent no 4499384 1985
[29] C C Chen D Fang and Z Luo ldquoFabrication and characteriza-tion of highly-ordered valve-metal oxide nanotubes and theirderivative nanostructuresrdquo Reviews in Nanoscience and Nan-otechnology vol 1 no 4 pp 1ndash28 2012
[30] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions NACE Houston Tex USA 1974
[31] C W Lai and S Sreekantan ldquoEffect of applied potential onthe formation of self-organized TiO
2nanotube arrays and its
photoelectrochemical responserdquo Journal of Nanomaterials vol2011 Article ID 142463 7 pages 2011
[32] J H Lim and J Choi ldquoTitanium oxide nanowires originat-ing from anodically grown nanotubes the bamboo-splittingmodelrdquo Small vol 3 no 9 pp 1504ndash1507 2007
[33] J Tao J Zhao X Wang Y Kang and Y Li ldquoFabrication oftitania nanotube arrays on curved surfacerdquo ElectrochemistryCommunications vol 10 no 8 pp 1161ndash1163 2008
[34] D Kim F Schmidt-Stein R Hahn and P Schmuki ldquoGravityassisted growth of self-organized anodic oxide nanotubes ontitaniumrdquo Electrochemistry Communications vol 10 no 7 pp1082ndash1086 2008
[35] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons Singapore 1980
[36] G Wang Z Y Liu J N Wu and Q Lu ldquoPreparation and elec-trochemical capacitance behavior of TiO
2-B nanotubes for hy-
brid supercapacitorrdquoMaterials Letters vol 71 pp 120ndash122 2012[37] L Zhang Y Shi S Peng J Liang Z Tao and J Chen ldquoDye-
sensitized solar cells made from BaTiO3-coated TiO
2nano-
porous electrodesrdquo Journal of Photochemistry and PhotobiologyA vol 197 no 2-3 pp 260ndash265 2008
[38] XWei ldquoHydrothermal synthesis of BaTiO3thin films on nano-
porous TiO2covered Ti substratesrdquo Journal of Crystal Growth
vol 286 no 2 pp 371ndash375 2006[39] C-C Chen H-W Chung C-H Chen et al ldquoFabrication and
characterization of anodic titanium oxide nanotube arrays ofcontrolled length for highly efficient dye-sensitized solar cellsrdquoJournal of Physical Chemistry C vol 112 no 48 pp 19151ndash191572008
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Journal of Nanomaterials 9
[7] A S Shaikh and G M Vest ldquoKinetics of BaTiO3and PbTiO
3
formation from metallo-organic precursorsrdquo Journal of theAmerican Ceramic Society vol 69 no 9 pp 682ndash688 1986
[8] H Okamura andH K Bowen ldquoPreparation of alkoxides for thesynthesis of ceramicsrdquo Ceramics International vol 12 no 3 pp161ndash171 1986
[9] K W Kirby ldquoAlkoxide synthesis techniques for BaTiO3rdquoMate-
rials Research Bulletin vol 23 no 6 pp 881ndash890 1988[10] P Bhattacharya T Komeda K-H Park and Y Nishioka
ldquoComparative study of amorphous and crystalline (Ba Sr)TiO3
thin films deposited by laser ablationrdquo Japanese Journal ofApplied Physics vol 32 no 9 pp 4103ndash4106 1993
[11] D M Tahan A Safari and L C Klein ldquoPreparation and char-acterization of Ba
119909Sr1minus119909
TiO3thin films by a Sol-Gel techniquerdquo
Journal of the American Ceramic Society vol 79 no 6 pp 1593ndash1598 1996
[12] C-C Chen J-H Chen C-G Chao and W C Say ldquoElectro-chemical characteristics of surface of titanium formed by elec-trolytic polishing and anodizingrdquo Journal of Materials Sciencevol 40 no 15 pp 4053ndash4059 2005
[13] C-C Chen Y Bisrat Z P Luo R E Schaak C-G Chao andD C Lagoudas ldquoFabrication of single-crystal tin nanowires byhydraulic pressure injectionrdquo Nanotechnology vol 17 no 2 pp367ndash374 2006
[14] H Tsuchiya and P Schmuki ldquoSelf-organized high aspect ratioporous hafnium oxide prepared by electrochemical anodiza-tionrdquo Electrochemistry Communications vol 7 no 1 pp 49ndash522005
[15] I Sieber H Hildebrand A Friedrich and P Schmuki ldquoForma-tion of self-organized niobium porous oxide on niobiumrdquo Elec-trochemistry Communications vol 7 no 1 pp 97ndash100 2005
[16] I Sieber B Kannan and P Schmuki ldquoSelf-assembled poroustantalum oxide prepared in H
2SO4HF electrolytesrdquo Electro-
chemical and Solid-State Letters vol 8 no 3 pp J10ndashJ12 2005[17] N Mukherjee M Paulose O K Varghese G K Mor and
C A Grimes ldquoFabrication of nanoporous tungsten oxide bygalvanostatic anodizationrdquo Journal ofMaterials Research vol 18no 10 pp 2296ndash2299 2003
[18] G B Stefanovich A L Pergament A A Velichko and L AStefanovich ldquoAnodic oxidation of vanadium and properties ofvanadium oxide filmsrdquo Journal of Physics Condensed Mattervol 16 no 23 pp 4013ndash4024 2004
[19] N K Shrestha Y-C Nah H Tsuchiya and P SchmukildquoSelf-organized nano-tubes of TiO
2-MoO
3with enhanced elec-
trochromic propertiesrdquo Chemical Communications no 15 pp2008ndash2010 2009
[20] I Paramasivam Y-C Nah C Das N K Shrestha and PSchmuki ldquoWO
3TiO2nanotubes with strongly enhanced pho-
tocatalytic activityrdquoChemistrymdashA European Journal vol 16 no30 pp 8993ndash8997 2010
[21] A Ghicov S Aldabergenova H Tsuchyia and P SchmukildquoTiO2-Nb2O5nanotubes with electrochemically tunable mor-
phologiesrdquo Angewandte ChemiemdashInternational Edition vol 45no 42 pp 6993ndash6996 2006
[22] Y Yang D Kim M Yang and P Schmuki ldquoVertically alignedmixed V
2O5-TiO2nanotube arrays for supercapacitor applica-
tionsrdquoChemical Communications vol 47 no 27 pp 7746ndash77482011
[23] H Jha R Hahn and P Schmuki ldquoUltrafast oxide nanotube for-mation on TiNb TiZr and TiTa alloys by rapid breakdown an-odizationrdquo Electrochimica Acta vol 55 no 28 pp 8883ndash88872010
[24] WWei S Berger N Shrestha and P Schmuki ldquoIdeal hexagonalorder formation of self-organized anodic oxide nanotubes andnanopores on a Ti-35Ta alloyrdquo Journal of the ElectrochemicalSociety vol 157 no 12 pp C409ndashC413 2010
[25] H Tsuchiya S Berger J M Macak A Ghicov and P SchmukildquoSelf-organized porous and tubular oxide layers on TiAl alloysrdquoElectrochemistry Communications vol 9 no 9 pp 2397ndash24022007
[26] R J D Tilley ldquoCorrelation between dielectric constant anddefect structure of non-stoichiometric solidsrdquo Nature vol 269no 5625 pp 229ndash231 1977
[27] J Lin N Masaaki A Tsukune and M Yamada ldquoTa2O5thin
films with exceptionally high dielectric constantrdquo Applied Phys-ics Letters vol 74 no 16 pp 2370ndash2372 1999
[28] H Segawa K Mori M Itagati K Sakurki and T Ishiwta ldquoIm-age sensing devicerdquo US patent no 4499384 1985
[29] C C Chen D Fang and Z Luo ldquoFabrication and characteriza-tion of highly-ordered valve-metal oxide nanotubes and theirderivative nanostructuresrdquo Reviews in Nanoscience and Nan-otechnology vol 1 no 4 pp 1ndash28 2012
[30] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions NACE Houston Tex USA 1974
[31] C W Lai and S Sreekantan ldquoEffect of applied potential onthe formation of self-organized TiO
2nanotube arrays and its
photoelectrochemical responserdquo Journal of Nanomaterials vol2011 Article ID 142463 7 pages 2011
[32] J H Lim and J Choi ldquoTitanium oxide nanowires originat-ing from anodically grown nanotubes the bamboo-splittingmodelrdquo Small vol 3 no 9 pp 1504ndash1507 2007
[33] J Tao J Zhao X Wang Y Kang and Y Li ldquoFabrication oftitania nanotube arrays on curved surfacerdquo ElectrochemistryCommunications vol 10 no 8 pp 1161ndash1163 2008
[34] D Kim F Schmidt-Stein R Hahn and P Schmuki ldquoGravityassisted growth of self-organized anodic oxide nanotubes ontitaniumrdquo Electrochemistry Communications vol 10 no 7 pp1082ndash1086 2008
[35] A J Bard and L R Faulkner Electrochemical Methods Funda-mentals and Applications John Wiley amp Sons Singapore 1980
[36] G Wang Z Y Liu J N Wu and Q Lu ldquoPreparation and elec-trochemical capacitance behavior of TiO
2-B nanotubes for hy-
brid supercapacitorrdquoMaterials Letters vol 71 pp 120ndash122 2012[37] L Zhang Y Shi S Peng J Liang Z Tao and J Chen ldquoDye-
sensitized solar cells made from BaTiO3-coated TiO
2nano-
porous electrodesrdquo Journal of Photochemistry and PhotobiologyA vol 197 no 2-3 pp 260ndash265 2008
[38] XWei ldquoHydrothermal synthesis of BaTiO3thin films on nano-
porous TiO2covered Ti substratesrdquo Journal of Crystal Growth
vol 286 no 2 pp 371ndash375 2006[39] C-C Chen H-W Chung C-H Chen et al ldquoFabrication and
characterization of anodic titanium oxide nanotube arrays ofcontrolled length for highly efficient dye-sensitized solar cellsrdquoJournal of Physical Chemistry C vol 112 no 48 pp 19151ndash191572008
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials