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lI:AIMCm BAn[RY O( PARTMOO INsmUTE Of [l[CTROCHlM'SIfn' AND [N(RG" sysrUIS BLl6AltWl AC40UIY Of SCI["-C[S sor .... 1113 . BUlGARIA

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6th INTERNATIONAL CONFERENCE ON LEAD-ACID BATTERIES

LABAT'2005 13 -16 June 2005

Grand Hotel VARNA VARNA, BULGARIA

PROCEEDINGS (Extended Abstracts)

Organized by:

LEAD-ACID BATTERIES DEPARTMENT Institute of Electrochemistry and Energy Systems (CLEPS)

Bulgarian Academy of Sciences Sofia1113, BULGARIA

General Sponsor:

MONBAT PLC, Montana, Bulgaria

6th INTERNATIONAL CONFERENCE ON LEAD-ACID BATTERIES

LABAT'2005

ORGANIZER:

LEAD-ACID BATTERIES DEPARTMENT INSTITUTE OF ELECTROCHEMISTRY AND ENERGY SYSTEMS (CLEPS) BULGARIAN ACADEMY OF SCIENCES SOFIA 1113, BULGARIA

Chairman:

LOCAL ORGANIZING COMMITTEE

Prof. D. Pavlov, DSc Institute of Electrochemistry and Energy

Systems (CLEPS,) Sofia, Bulgaria

Scientific Secretary: Dr. G. Papazov, lEES, Sofia, Bulgaria

Secretary:

Members:

Mrs. M. Gerganska, lEES, Sofia, Bulgaria

Dr.B.Banov (lEES), ABobokov (MONBAT PIc), L.Bogdanova (lEES), Dr.AGigova (lEES), Dr.M.Dimitrov (lEES), D.lvanova (lEES), I,Karageorgiev (MONBAT Trading), Dr.AKirchev (lEES), Dr.M.Matrakova (lEES), Dr.AMomchilov (lEES), Dr.V.Naidenov (lEES), Dr.G.Petkova (lEES), Dr.T.Rogachev (lEES), Dr.S.Ruevski (lEES), G.Sheitanov (lEES), Dr.D.Valkovska (lEES), Dr.S.Vassilev (lEES)

GENERAL SPONSOR

MONBAT PLC, Montana, Bulgaria

INTERNATIONAL ADVISORY COMMITTEE

Dr. V. Bolotovsky, Accumulator Institute "/stochnik", Russia

Dr. A.Cooper, Lead Development Association, UK

Prof. A.Czerwinski, Warsaw University, Po/and

Dr. J. Devitt, Gonsu/ant, USA

Or. I. Dyson, GMP Batteries, UK

Or. H.K. Giess, Accumulatoren-Fabrik Oer/ikon, Switzer/and

Prof. Y. Guo, Fuzhou University, China

Dr. J. Kamenev, JSC "Eketrotyaga", Russia

Dr. L. Lam, GS/RO, Australia

Prof. Weishan Li, South China Norma/ University, China

Or. E. Meissner, VARTA Autobatterie GmbH, Germany

Prof. J. Morales, Cordoba University, Spain

Prof. G. Nauer, Universi(y o{ Vi~f\f\a, AusMja

Dr. R.F. Nelson, Recombination Technologies, USA

Dr. S. Osumi, GS Japan Storage Batteries, Japan

Dr. M. Perrin, CEA-GENEC, France

Dr. D. Prengaman, RSR Technologies Inc., USA

Or. J. Pierson, Johnson Controls, Inc., USA

Mr. A. Shaefer, Bitrode Corporation, USA

Mr. Rob Sheridan, Bartenes InternatIonal, UK

Dr. M. Shiomi, GS Yuasa Corporation, Japan

Dr. V. Smirnov, NIISTA, Russia

Prot. P. Spinelli, Politecnico di Torino, Italy

Prof. Zen-ichiro Takehara, Kansai University, Japan

Or. L. Torcheux, CEAC, France

Or. F. Trinidad, Tudor SA/Exide Technologies, Spain

Prof. A. Velichenko, Ukrainian State Univ. of Chem. Technol., Ukraine

Dr. R. Viswanathan, TAFE, India

Dr. L. Yolshina, Russian Academy of Sciences, Russia

Dr. G. Zguris, Hollingsworth & Vose Co., USA

GASTON PLANTE MEDAL

The Gaston Plante Medal will be awarded to the next recipient, selected by an International Plante Medal Committee, for significant contribution to the development of lead-acid battery science and technology.

GASTON PLANTE MEDAL COMMITTEE

Dr. K.Bullock, , Coolohm Inc., USA Prof. K.D'Alkaine, Federal University of Sao Carlos, Brazil Prof. B. Grafov, Russian Academy of SCiences, Russia Prof. N. Hirai, Osaka University, Japan Dr. E.Karden, Ford R&D Centre Aachen, Germany Dr. K.Micka, J.Heyrovsky Institute of Physical Chemistry, Czech Republic Dr. P.Moseley, ILZj10IALABC, USA Prof. D.Pavlov, lEES (CLEPS), Bulgaria Dr. K.Peters, Consultant, UK Dr. D.A.J. Rand, CSIRO, Australia Prof. P.Ruetschi, Leclanche S.A.lConsultant, Switzerland Prof. M. Shiota, GS Yuasa Corporation, Japan Prof. A. Shukla, CECRI, India Prof. M. Steinmetz, University of Nancy, France Dr. Z. Wang, Beijing University of Science and Technology, China

GASTON PLANTE MEDALLISTS

Dr. Ernst Voss, VARTA Batterie AG, Germany 1989 Dr. Paul Ruetschi, Leclanche S.A., Switzerland 1993 Prof. Detchko Pavlov, CLEPS, Bulgaria 1994 Dr. Kathryn Bullock, Medtronic, Inc., USA 1996 Dr. David A.J. Rand, CSIRO, Australia 1996 Dr. Norman Bagshaw, NEB Consultants, UK 1999 Mr.John Devitt, Consult. Electrical Engineer, USA 1999 Dr. David Prengaman, RSR Corporation, USA 2002 International Lead Zinc Research Organization, USA 2002

2005 GASTON PLANTE MEDAL NOMINEES

Dr. Masaharu Tsubota, GS Yuasa Corporation, Japan Prof. Zen-Ichiro Takehara, retired from Kansai University, Japan Prof. Karel Micka, Heyrovsky Inst. of Physical Chemistry, Prague, Czech Republic Dr. Kenneth Peters, Consultant, UK

NEW GRIDS

18 Lead film electrode as negative and positive plate of lead-acid battery 77 L.A Yoishina

19 Porous glassy carbon modified with metals and their oxides as electrode 81 materials in batteries. Selected electrochemical properties

A Czerwinski, J. Kotowski, Pruszkowska-Drachal, IPaleska, ZRogulski

20 Lead-acid batte(ies with foam grids 85 S.M. Tabaatabaai, M.S.Rahmanifar, S.AMousavi, S.Shekofteh, Jh.Khonsari, H. Tabrizi, A Tizpar, S.Shirzadi, N.Bashiri

21 Effect of lead foam grid on performance of VRLA battery 89 C.S.Dai, T.F. Yi, D.L. Wang, XG.Hu, (poster)

22 Simultaneous optimization of the properties of engineered composite 93 grids for lead-acid batteries

H. Warlimont, T.Hofmann

23 A low-cost lead-acid battery with high specific energy 97 S.K.Martha, B.Hariprakash, S.AGafoor, AK.Shukla

LEAD ALLOYS

24 Microstructure of new lead-acid electrode alloys 101 I.Mukaitani, H. Tsubakino, L.Liu, A Yamamoto, S.Fukumoto

25 Oxygen evolution reaction on lead-bismuth alloys in sulfuric acid solution 105 W.S.Li, XM.Long, F.H.Wu, Y.M.Wu, H.Y.Chen, J.H.Yan, R.Zhang

26 Application and properties of lead-calcium-tin-bismuth alloys for positive 109 grids

J.Liang, H.Chen, Y. Wu, G.Xiao, H.Zhou, (poster)

27 Electrochemical behavior of lead alloys in sulfuric and phosphoric acid 113 electrolyte

S.Li, H.Chen, Y. Wu, W.Li, XJiang, M. Tang, W. Wei, Zhuzhou

28 Influence of alloying elements on electrochemical and oorrosion behaviors 117 of Pb grid alloys

C.Ramirez, J.M.Hal/en-Lopez, H.Dorantes-Rosales, U.Santiago, E.M.Arce

29 Corrosion of low-antimony lead-cadmium alloys in conditions of long-term 121 polarization

A Nuzhny

BATTERY TESTING

30 Testing challenges in the HEV laboratory: Integrating External Data 125 Streams

R.Schaefer

31 Thermal analysis of lead-acid battery pastes and active materials 129 M.Matrakova, D.Pavlov

32 Internal battery temperature estimation using series battery resistance 135 measurements during cold temperatures

A Han de

33 Potentiometric measurement of state-of-charge of lead-acid battery by 139 using a bridged ferrocene surface modified electrode

T.B./ssa, P.Singh, M. V.Baker (poster)

139

Potentiometric measurement of state of charge of Lead-Acid battery by using a bridged ferrocene surface modified electrode

Touma B. Issa*, Pritam Singh*, Murray V. Baker# * Division of Science and Engineering, Department of Chemistry, Murdoch University, WA 6150,

Australia # Department of Chemistry, University of West em Australia, Crawley, W.A. 6009, Australia

Abstract

2-(Il-mercaptoundecyl) [3 }(J,l ')ferrocenophane, BSFc (I) and 3-(1J -mercaptoundecyl) [S}(J, J ') ferrocenophane, BSFc (II), were synthesized and their electrochemical behaviour in aqueous sulphuric acid electrolyte investigated. It is found that these compounds, chemisorbed on a gold substrate, undergo reversible oxidation/reduction. The anodic and cathodic peak potentials are found to be independent of the acid concentration in the range (J.OxJ(J2 to IxI(J7 mol L-1

) but change linearly with the acid concentration in the range 1 to SM. While this behaviour is similar to that for other ferrocenes, the materials are much more chemically stable in aqueous sulphuric acid media. The presence of thiol group enhances the retainability of the bridged ferrocenes on gold surface. The possibility of applying this observation for determining state of charge of lead-acid battery is discussed.

Keywords: surface modified; electrodes; ferrocene ferrocenium redox couple electrode; Bridged ferrocene; State of charge; Lead Acid battery.

Introduction

The ferrocene/ferricinium (Fc/Fc +) couple is a well known reference electrode for electrochemical studies [1, 2]. It is based upon the fact that ferrocene undergoes a reversible redox reaction according to Eq 1 which, does not involve H+ ions.

Hence the redox potential of the FcfFc+ couple is independent of H+ concentration. However the ferricenium cation is soluble in aqueous solutions and is susceptible to various decomposition reactions. This instability limits the use of FcfFc+ couple in electrochemical sensors and other devices for use in aqueous media. We reported earlier [3] that the solubility and instability of FclFc+ in aqueous media could be overcome by using ferrocene derivatives in which the two cyclopentadienyl rings are bridged by hydrocarbon chains consisting of methylene groups fCH2fn where n=3 or 5. We found that such bridged ferrocenes (BFc), were chemically stable but could not be efficiently retained at the surface of an inert substrate [3]. Thus such ferrocene derivatives were not suitable for making appropriate surface modified electrodes (SME's).

With the view to improving the retainability of the BFc at electrode surface, we have considered incorporation of alkanethiol [fCH2fllSH] groups into the bridged ferrocene molecule (BSFc). The sulphur atom in the -SH group of BSFc is expected to have a strong interaction with metals like gold [4]. Hence coating gold with BSFc could be the way to construct a robust SME for use in aqueous media.

This paper describes the results of a systematic study of the electrochemistry, and chemical stability of BSFc in concentrated (1-5 M) aqueous H2S04 media. The underlying objective of the work was to investigate whether the BSFcfBSFc+ couple could be used as a SME for monitoring changes in H2S04 concentration which in turn could be used for determining state of charge of Lead-acid batteries.

140

Experimental

All solutions were prepared by dissolving commercially available analytical grade chemicals in high purity water obtained from a Millipore Milli-Q system. All the chemicals were used as received. The ferrocene derivatives (Figure 1) were synthesized in our laboratory by using standard techniques as reported in the literature [5-8]. A polycrystalline gold electrode (99.99% fine gold; Australian Gold Refineries, Perth.) was used as a substrate. BSFc coated on gold SME's were prepared by adopting a procedUre similar to that reported in the literature [9]. The gold surface was cleaned by polishing with silicon carbide waterproof papers grades 800, 1200, followed by dipping into aqua regia for 1 minute. The cleaned electrode was then potentiostated for 5 minutes at -0.9 Y vs SCE in l.0 mol L-1 H2S04 where hydrogen gas evolved vigorously at the electrode surface. A platinum wire was used as a counter electrode. The potentials were measured against a saturated calomel electrode (SCE) and quoted as such. All investigations were carried out under nitrogen atmosphere.

(CH

BSFc (I) BSFc (II)

Figure I: BSFc structural formula.

Results and Discussion

Figure 2 shows typical cyclic voltammograms for BSFc(J) and BSFc(II). As can be seen, for both the ferrocenes symmetrical oxidation-reduction peaks corresponding to one electron transfer were obtained. The experimental anodic and the cathodic peak potential values are noted in Table 1. The , corresponding values for the same ferrocenes without the -SH group are also included in Table 1.

Table 1: Cyclic voltammetry parametersfor BSFc(1) and BSFc(11 Ferrocene Epa** Epc llEp

mY mY mY BSFcI 415 (90) 400 (40) 15 (50) BSFcII 380 (120) 365 (55) 15 (65)

** The relevant data for the corresponding BFc compounds are given in the parenthesis.

As can be seen from the data in Table 1 the anodic and the corresponding cathodic peak potentials shifted to more positive values when -SH group was attached to the ferrocene. The llEp (Epa -Epc) values approached zero suggesting that the -SH group improved the adhesion of the ferrocene to the substrate so that the electrode behaved more like a truly reversible surface modified electrode.

The log anodic current (IPa) vs log scan rate (v) plots were found to be linear with slope ca. 0.86 Acm-2 per unit Ys-1scan rate for both BSFc(J) and BSFc(II). The slopes are very close to the theoretical value of 1.0, indicative of a reversible redox process involving a species immobilised at the surface of an electrode [10].

L-__ ~ __ ~ __ ~~ __ ~ __ ~ __ ~

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Potential vs seE I v Figure 2a Cyclic voltammogram of 2-(11-mercaptoundecyJ)[3](1,1 ')ferrocenophane, BSFc (I) in 1.0 M H2S04 on a gold electrode (sweep rate 100 mVs- J

).

141

+ 0.0 0.1 0.2 0.3 0.4 0.5 0.6

Potential vs SeE I v

Figure 2b Cyclic voltammogram of 3-(11-mercaptoundecyJ)[S)(l,l ')ferrocenophane, BSFc (II) in 1.0 M H2S04 on a gold electrode (sweep rate 100 mVs-1

).

The dependence of EPa of both BSFc(I) and BSFc(II) on H2S04 concentration can be seen from the results in Figure 3. As can be seen the Epa values were independent of the acid concentration in the range (1.0xlO-2 to lx10-7 mol L-1

). However the peak potential values shifted linearly to less positive potentials as the acid concentration increased from 1 to 5 M (Figure 3). The slopes of the plots for both the ferrocenes were 24 m V per unit molar concentration of the acid.

> ~

LIl u t/l

"' " '" 0-LIl

0.50

0.45

0.40

0.35 ---o BFc I

0.30 • BFc II --... _--.

0.25

~ ~ ~ ~ 0 ~ ~ ~ 0 w w ~ ~ ~ w ij ~ ~ ~ ~ ~ ~ ~ ~ ,. ~ ~

Acid Concentration / M

Figure 3 The anodic peak potential against concentration of sulphuric acid for BSFc I and II.

c 0

~ Oll 100 .i§ 8 .- c.S 80 '" ... E ;::l

~

'" '" 60 ""t:l

.... '" :§]

OBFcI ... ... 40 '" ~ ~ C)

• BFc II '" '" EO:; 20 <1J <1J

..c:..c: ~ ~

4-< 0 0

~ 0 0 20 40 60 80 100

Number of Cycles

Figure 4 Percent of the residual material on the electrode surface of ferrocene against number of cycles in 1 M H2S04•

As noted earlier, a major objective of this study was to establish whether the presence of a fCH21 I I SH group in a BFc molecule improves the retainability of BFc on a gold substrate. This property was, investigated by subjecting the two ferrocenes c-oated on gold, to repeated voltammetric cycling in the potential range 0.0 - 0.6 V in 1.0 M H2S04. The IPa for each cycle was measured and the data used to calculate, (Ipa)nI(Ipa) 1 xl 00, where n is the cycle number. The function (Ipa)n/(IPa)I x 1 00 defines the percentage of the electro active material left at the electrode surface at each cycle. These data are plotted in Figure 4. As can be seen 68% of the BSFc(I) and 72% of BSFc(II), were retained at the electrode surface at the 100th cycle. This compares with 2% left on the electrode surface under similar conditions for the bridged ferrocenes without the -SH attachment. Clearly the attached -SH groups increases the retainablity of the active ferrocene molecules on the surface of gold. Thus the BSFc(I) and BSFc(II) both have the potential for being

142

used as stable electroactive couples in concentrated H2S04 media and being used for monitoring state of charge of lead-acid batteries potentiometrically.

Conclusion

Cyclic voltammetric behaviour of alkanethiol bridged ferrocenes BSFc(I) and BSFc(II) coated on a gold substrate is found to be very similar to what would be expected of a truly reversible surface irnmobilised redox couple. Th~ Epa values were independent of H2S04 acid concentration in the range (1.0xl0-2 to lxl0-7 mol L-1

). However, they shifted linearly to less positive values as the acid concentration increased to the range 1-5 molar. The incorporation of -SH group increased the retainablity of the ferrocenes on gold substrate considerably. The materials have potential for being used as potentiometric sensors for determing state of charge oflead-acid batteries.

References

[1] J. K. Bashkin and P. J. Kinlen, Inorganic Chemistry 29:4507 (1990). [2] G. Gritzner and J. Kuta, Pure & Appl Chern 56:461 (1984). [3] T. B. Issa, P. Singh, M. Baker, S. 1. Baily, and B. S. Verma, Proceedings - Electrochemical

Society 93-7:268 (1993). [4] R. G. Nuzzo and D. L. AHara, J. Am. Chern. Soc. 105:4481 (1983). [5] T. H. Barr and W. E. Watts, Tetrahedron 24:3219 (1968). [6] C. D. Bain, E. B. Troughton, Y. T. Tao, J. Evall, G. M. Whitesides, and R. G. Nuzzo, J. Am.

Chern. Soc. ill:321 (1989). [7] Y. Okahata, G. Enna, and K. Takenouchi, J. Chern. Soc., Perkin Trans. 2:835 (1989). [8] K. L. Rinehart, Jr., R. J. Curby, Jr., D. H. Gustafson, K. G. Harrison, R. E. Bozak, and D. E.

Bublitz, J. Am. Chern. Soc. 84:3263 (1962). [9] J. J. Hickman, D. Ofer, C. Zou, M. S. Wrighton, P. E. Laibinis, and G. M. Whitesides, J.

Am. Chern. Soc. 113:1128 (1991). [10] M. E. Gomez and A. E. Kaifer, J. Chern. Educ. 69:502 (1992).

H.Abedinpour - 73 N.Abolhasani - 65 I.Abrahams - 261 S.Afifi - 255 R.Amadeli - 237 S.Ambalavanan - 39 M.Amin -65 J.de Andrade - 147 E.M.Arce - 117 P.Baca - 167 M.V.Baker - 139 B.Banov - 261,265 N.Bashiri - 85 K.Belov - 143 W.Boehnstedt - 205 J.Boesler - 205 ACabaliero - 229,233 M.Calabek -167 H.Catherino - 11 H.Y.Chen - 105, 109, 113 N.Cruz - 229,233 ' A.Czerwinski - 81 C.S Dai - 89 C.D'Alkaine - 147 F.I.Daniiov - 237 AD,Dayanov - 175 J.Deiters - 205 ADelailie - 185 Q.DengKe - 51 D.Devilliers - 237 H.Dorantes-Rosales-117 P-Drachal - 81 D.Edwards - 57 AEmori - 221 P.Farina - 157 AFerreira - 33 R. Fitas - 245 S.Fukumoto - 101 S.AGafoor - 97 C.Garcia - 153 N.Gharib - 65 M.Ghaemi - 251 E.Ghafouri - 251 A.Gigova - 25, 209 F.Gobal- 61 Y.Guo - 29 J.M.Halien-Lopez - 117 AHammouche -15 A Hande - 135 B.Hariprakash - 97 F.Heikal - 255 M.Hejabi - 65,73 N.Hirai - 159 T.hirasawa - 221 T.Hofmann - 93 J.Hu - 29

AUTHOR'S INDEX

X.G.Hu - 89,225 M.Huang - 29 F.Huet-181,185 K.lhmels - 205 T.lkeda - 159 P.Rlmpinnisi - 147, 153 T.B.lssa -139 M.G.lvanov - 175 X.Jiang - 113 H.Karami - 69 E.Karden - 189 M.AKarimi - 69 Jh.Khonsari - 85 AKirchev - 5, 19, 25 J. Kotowski - 81 A Kozera - 153 P .Krivak - 167 P.Lailler - 181 K.Lamm - 217 V.F.Lazarev -175 E.Lemaire-Potteau - 43 S.Li - 113 W.S.Li-47, 105, 113 J.Liang - 109 L.Liu - 101 X.M.Long - 105 t.V.Luk'yanenko - 237 K.Magara - 159 M.Mahdipour - 69 V.B.Malkov - 175 S.K.Martha - 97 M.Matrakova - 129 K.Micka - 167 M.Mladenov - 143 A.Momchiiov - 261,265 B.Monahov - 5 H.Moqtaderi - 65 J.Morales - 229,233 AMosahebi - 65 S.AMousavi - 85 I.Mukaitani - 101 NV.Nikolenko - 241 P.Nikolov - 171 RP.Nogueira - 181 ANuzhny - 121 T.Okoshi - 221 AOweisi - 73 I. Paleska - 81 G.Papazov - 43,209,261 D.Pavlov - 5, 19,25,43,

129, 171 M.Perrin - 185 G.Petkova - 171,229,233 J.Pierson - 1 B.Puresheva - 261 M.S.Rahmanifar - 85

C.Ramirez - 117 Z.Rogulski - 81 S.M.Tabaatabaai - 85 ASaba - 255 U .Santiago - 117 J.F.Sarrau - 43 D.U.Sauer -15, 189 RSchaefer - 125 A Schwetz - 213 S.Shekofteh - 85 A.Shenouda - 255 S.Shirzadi - 85 AK.Shukla - 97 P.Singh - 139 L.M.de Souza - 147, 153 T.Suntio - 193 E.Surewaard - 189 H.Tabrizi - 85 T.Tanaka - 159 M.Tang -113 ATenno - 193 R.Tenno -193 M.Thele - 15, 189 A.Tizpar - 85 V.Toniazzo - 199 F.Torabi - 65 L.Torcheux - 181 F.Trinidad - 163 H.Tsubakino - 101 C.Tzeciuk - 153 JValenciano - 163 DValkovska - 5, 19, 25 X.Va\lve-43 Van der Borg - 43 S.Vassilev - 261 AB.Velichenko - 237,241 C.I Wang -47 D.L.Wang - 89 H.Warlimont - 93 W.Wei -113 F.H.Wu -105 Y.M.Wu-105, 109, 113 G.Xiao -109 K.Yamada - 221 AYamamoto - 101 J.H.Yan - 47,105 Z.Yan - 225 T.F.Yi - 89 L.Yolshina - 77 Y.P.Zaikov - 175 L.Zerroual - 245 Q.y.zhan 47 S.zhang - 57, 105 H.Zhou -109 ZhuZhou - 113

Figure 2a - Cyclic voltammogram of 2-(11-mercaptoundecyI)[3](1.1')ferrocenophanes.BSFc (I) in 1.0 M H2SO4 on a gold electrode (sweep rate 100 mVs-1)

Figure 2b - Cyclic voltammogram of 3-(11-mercaptoundecyI)[5](1.1')ferrocenophanes.BSFc (II) in 1.0 M H2SO4 on a gold electrode (sweep rate 100 mVs-1)

Figure 1 - BFc and BSFc general structural formula

Figure 4 - Percent residual BSFc (I) and BSFc (II) on the electrode surfaceversus cycles number in 1.0 M H2SO4

% R

esid

ual B

SFc(

I)an

d BS

Fc(II

)

Figure 3a - The anodic peak potential concentration of (1.0 x 10-2 to 1.0 x 10-7 M) sulphuric acid for BSFc (I) and BSFc (II)

Epa v

s SCE

/V

Figure 3b - The anodic peak potential versus concentration (1-5 M) ofsulphuric acid for BSFc (I) and BSFc (II)

Epa v

s SCE

/V

Touma B. Issa*, Pritam Singh*, Murray V. Baker#* Division of Science and Engineering, Department of Chemistry, Murdoch University, WA 6150, Australia# Department of Chemistry, University of Western Australia, Crawley, W.A. 6009, Australia

AbstractAlkanethiol bridged, 2-(11-mercaptoundecyl)[3](1,1') ferrocenophanes, BSFc (I) and 3-(11-mercaptoundecyl) [5](1,1') ferrocenophane, BSFc (II), were synthesized and their electrochemical behaviour in aqueous sulphuric acid electrolyte investigated. It is found that these compounds, chemisorbed on a gold substrate, undergo reversible oxidation reductions. The anodic and cathodic peak potentials are independent of the acid concentration in the range 1.0x10-2 to 1.0x10-7 M but change linearly with the acid concentration in the range 1 to 5 M. While this behaviour is similar to that for other ferrocenes, the materials are much more chemically stable in aqueous sulphuric acid media. The presence of thiol group enhances the retainability of the bridged ferrocenes while maintaining their chemical stability. The possibility of applying this observation for determining state of charge of lead-acid battery is discussed.

IntroductionThe State of Charge of Lead acid batteries is often determined by labour intensive method such as measuring specific gravity of the battery electrolyte. Such methods are not amenable to remote sensing, a feature which is most desirable for large battery installation in inaccessible locations. The potentiometric monitoring of H+ concentration as a function of state of charge of the battery would be an attractive alternative. Unfortunately the tradition pH measuring devices cannot be used in concentrated H2SO4 solutions and therefore development of more suitable probes is desired.

With this objective, we are investigating whether Surface Modified Electrodes (SME) made from organic redox couples, such as ferrocene/ferricenium including their derivatives would be appropriate for this application. This paper describes the findings of our work on the bridged ferrocene surface modified electrode couples.

ExperimentalThe ferrocene derivatives (Figure 1) were synthesized in our laboratory by using standard techniques as reported in the literature 1-4. The electrodes (SME's) were prepared by adopting a procedure similar to that reported in the literature 5. The potentials were measured against a saturated calomel electrode (SCE) and quoted as such. All investigations were carried out under nitrogen atmosphere.

Results and DiscussionThe ferrocene/ferricinium (Fc/Fc+) is a well known reference couple for electrochemical studies 6, 7. It is based upon the fact that ferrocene undergoes a reversible redox reaction according to Eq1 which, does not involve H+ ions.

However solubility and instability of the ferricenium cation in aqueous solutions limits the use of Fc/Fc+ couple in electrochemical sensors. We reported earlier 8 that the solubility and instability of Fc/Fc+ could be overcome by using bridged ferrocene derivatives in which the two cyclopentadienyl rings were linked by (CH2)n chains. We found that such bridged ferrocenes (BFc), were chemically stable but could not be retained at the surface of an inert substrate 8. With the view to improving the retainability of the BFc at the electrode surface, we have considered the use of derivatives of BFc formed by incorporating alkanethiol [(CH2)11SH] groups into the bridged ferrocene molecule. The sulphur atom in the -SH group in the derivatives (BSFc(I) and BSFc(II)) as shown in Figure 1 is expected to have a strong interaction with metals like gold 9. Hence coating gold with BSFc could be the way to construct a robust SME for use in aqueous media.

Figure 2 shows cyclic voltammograms for BSFc(I) and BSFc(II). As can be seen symmetrical oxidation-reduction peaks corresponding to one electron transfer were obtained for both.

Figure 3a shows the Epa of both BSFc(I) and BSFc(II) was independent of the H2SO4 concentration in the range 1.0x10-2 to 1.0x10-7 M. However the peak potential values were found to shift linearly to less positive potentials as the acid concentration increased from 1 to 5 M (Figure 3b). The potentials were reproducible and hence could be related to the acid concentration. The chemical stability of BSFc(I) and BSFc(II) were investigated by subjecting them to repeated cyclic voltammetric scans in the potential range 0.0 - 0.6 V in 1.0 M H2SO4 electrolyte.

Figure 4 shows the percentage of residual ferrocene on the electrode surface as function of cycle number for the first 100 cycle's in1.0 M H2SO4. 32% of the BSFc(I) and 28% of BSFc(II), was lost from the electrode surface at the 100th cycle. This compares with the 98% loss under similar conditions for the bridged ferrocenes without the -SH attachment. Clearly the attached -SH groups increases the retainability of the active ferrocene molecules on the surface of gold. Thus the BSFc(I) and BSFc(II) both have the potential for being used as stable electroactive couples in concentrated H2SO4 media and being used for monitoring state of charge of lead-acid batteries potentiometrically.

ConclusionCyclic voltammetric behaviour of alkanethiol bridged ferrocenes BSFc(I) and BSFc(II) coated on a gold substrate is found to be very similar to what would be expected of a truly reversible surface immobilised redox couple. The Epa values do not vary with H2SO4 acid concentration in the range 1.0x10-2 to 1.0x10-7 M. However, they shift linearly to less positive values as the acid becomes more concentrated in the range 1-5 molar. The incorporation of -SH groups increases the retainability of the ferrocenes on gold substrate. These ferrocenes thus have a potential for being used as potentiometric sensors for determining state of charge of lead-acid batteries.

References(1) Barr, T. H.; Watts, W. E. Tetrahedron 1968, 24, 3219-3235.(2) Bain, C. D.; Troughton, E. B.; Tao, Y. T.; Evall, J.; Whitesides, G. M.; Nuzzo, R. G. J. Am. Chem. Soc. 1989, 111, 321-335.(3) Okahata, Y.; Enna, G.; Takenouchi, K. J. Chem. Soc., Perkin Trans. 2 1989, 835-843.(4) Rinehart, K. L., Jr.; Curby, R. J., Jr.; Gustafson, D. H.; Harrison, K. G.; Bozak, R. E.; Bublitz, D. E. J. Am. Chem. Soc. 1962, 84, 3263-3269.(5) Hickman, J. J.; Ofer, D.; Zou, C.; Wrighton, M. S.; Laibinis, P. E.; Whitesides, G. M. J. Am. Chem. Soc. 1991, 113, 1128-1132.(6) Bashkin, J. K.; Kinlen, P. J. Inorganic Chemistry 1990, 29, 4507-4509.(7) Gritzner, G.; Kuta, J. Pure & Appl Chem 1984, 56, 461-466.(8) Issa, T. B.; Singh, P.; Baker, M.; Baily, S. I.; Verma, B. S. Proceedings - Electrochemical Society 1993, 93-7, 268-274.(9) Nuzzo, R. G.; Allara, D. L. J. Am. Chem. Soc. 1983, 105, 4481-4483.

Potentiometric measurement of state of charge of Lead-Acid battery by using a bridged ferrocene surface modified electrode