Fabrication of electrospun PVA-KCl nanofibers as Electric

Double Layer Capacitor and electrochemical analysis for

application as solid polymer electrolyte

K.Vinotha1, V.SenthilKumar

2 , S.Muruganand

3, K.Sriram

4

Research Scholar and Associate Professor, Department of Physics, Karpagam Academy of Higher Education,

Coimbatore, Tamil Nadu, India1,2

Assistant Professor and Lecturer, Department of Electronics and Instrumentation, Bharathiar University,

Coimbatore, Tamil Nadu, India3,4

ABSTRACT

The fabrication of PVA-KCl nanofiber as EDLC for energy storage is done by electrospinning

technique. Nanofibers have large surface area to volume ratio and are porous which make them

ideal for charge storage and ion transportation .The SEM images of the samples with different

doping levels of KCl clearly show that higher doping concentration leads to bead formation that

enhances the conductivity of the membrane. The doping of KCl with PVA increases the

conductivity of the membrane and enhances the crystalline nature of the material, AC

conductivity studies and XRD analysis were done to further understand the properties of the

sample with different doping concentration. The conductivity graph shows greater conductivity

for S3 with greater doping concentration. Electrochemical storage capacity of the samples is

determined by linear sweep voltammetry. The cathodic and anodic voltage range of less

decomposition occur in sample S1 from -1V to +1V which have slightly doped with KCl. The

samples S2 and S3 exhibit range from -1.7V to +1.5V. The specific capacitance of S3 was found

by cyclic voltammetry analysis. The measured Cspec value is around 2.9518 Fg-1

.The structural

and electrochemical analysis confirm that PVA-KCl nanofiber can be used as polymer

electrolyte and EDLC.

KEYWORDS

Polyvinyl alcohol, Poly Vinyl Pyrollidine, Linear Sweep Voltammetry, Ionic conductivity,

Cyclic Voltammetry, Electrospinning.

INTRODUCTION

The application of electrospun

nanofibers as Electric Double Layer

Capacitors [EDLC] in energy storage and

fuel cell developments increases the

versatility and fulfills the demand for

improved efficiency and costs less [1]. The

ion exchanging membrane is an essential

part in battery applications and it acts as

both electrolyte and separator. The main

focus of this research is the electrochemical

analysis of combined electrospun Poly Vinyl

Pyrollidine[PVP], Poly Vinyl Alcohol

[PVA] doped potassium chloride[KCl]

nanofiber, which is pure biodegradable

International Journal of Pure and Applied MathematicsVolume 119 No. 15 2018, 1145-1153ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

1145

polymer blend nanofiber that conducts

protons and can be used as solid-gel

polymer electrolyte for electrochemical

energy storage and generation[2,3]. The

polyethylene oxide electrospun nanofiber

structures have been used in many of the

latest polymer lithium ion battery as

separators which separate the electrolyte and

the electrode terminals [4]. Using the

electrospun nanofiber material in lithium ion

capacitors [LIC] makes it compact which

enables more energy storage with high

charge density. The main advantage of

electrospun nanofibers as separator and

electrode is the larger surface area which

adsorbs electrolytes through its porosity.

Electrospun nanofiber PVA in the form gel

without losing its mechanical stability could

produce hydroxyl group and has higher

charge storage capacity which can be

encapsulated by doping salts and aids in

formation of microcrystals and nanocrystals

depending on the concentration of the

doping. Hence PVA blend is suitable for the

wet electrochemical charge storage and for

EDLC. In addition the doping of PVA with

salts could also enhance the ionic

conductivity and electrochemical properties

of the nanofibers membrane so that it can act

as a very good dielectric separating

membrane and also as an electrolyte for

EDLC [5]. And in application of fuel cells,

nanofibers give porous membrane polymer

electrolyte suitable for Hydrogen ion [H+]

storage. With these enhanced properties, the

porous nanofiber electrolyte membrane can

also be used in fuel cell for Hydrogen ion

(H+) storage applications [6,7]

METHODOLOGY

PVA-PVP based electrospun

nanofibers have been prepared and the

electrochemical characteristics have been

analyzed for different doping concentrations

of KCl. The structural studies were done to

confirm the formation of crystalline

nanostructures. The PVA-PVP-KCl doped

nanofiber membrane has been fabricated

using electrospinning method. The solution

of PVA with 10 wt% is prepared and the

three different doping concentration of KCl

added. KCl is added with three separate

25ml solutions prepared with 10 wt% such

that one gram added to sample S1, three

grams added to sample S2 and five grams

added to sample S3 and then three samples

are subjected to electrospinning in the

electrospinning device with constant

distance of 7 cm between tip and collector

and applied voltage of 30KV. Three

nanofiber samples S1, S2, S3 were obtained

with dimensions of 5 cm x 5 cm after one

and half hour with a flow rate of 3 milliliter

(ml) per hour of the polymeric solution. The

samples are analyzed by characterizing with

Scanning Electron Microscopy [SEM], X-

ray Diffraction [XRD], AC conduction

studies, Linear Sweep Voltammetry [LSV]

and one highly doped sample S3 with Cyclic

Voltammetry (CV).

RESULT AND DISCUSSIONS

SEM analysis

Analyzing the three samples it is evident

that addition of dopant results in the

formation of nanocrystals i.e. beads in the

nanofibers during electrospinning because of

the encapsulation of salts on the PVA-PVP

blends. Formation of nano or microcrystals

is found to be more in sample 3 than in

sample 2 and sample 1. In general,

increasing the salt concentration in a

solution would increase the size of crystals

and also more number of crystals is formed.

But there is an increase in the slender

property of fibers in sample 1 than in the

other samples. Hence the increase in salt

concentration affects the slender property of

the nanofibers because of discontinuous

electric field discharge between the tip and

the collector in the electrospinning method.

International Journal of Pure and Applied Mathematics Special Issue

1146

But formation of mesh type structure of the

nanofibers with less diameter is desired for

higher porosity so that the surface

adsorption is better and conductivity of the

nanofibers can be improved which is

possible only by increasing the doping

concentration

Figure 1: SEM images [3µm and 5µm] of three

differently doped concentration of KCl (a) Fibers

from sample S1 (b) fibers from sample S2 and (c)

fibers from sample S3.

XRD analysis

In the 180ºC calcinated sample of S3,

XRD peak clearly shows that the high

intensity is obtained at 2Ɵ of 28 deg.

Whereas in the uncalcinated sample there

are more number of peaks and the high

intensity peak is spread across the range

from 15 to 32 deg of 2Ɵ .This shows the

higher crystalline nature of PVA because of

the addition of salt KCl into it. In general

PVA is crystallized on calcinations of 85ºC

to 100ºC. Hence addition of salts increases

the conductivity as well as crystalline nature

of PVA-PVP membrane prepared. Also this

blend has the release of proton conductivity

because of PVP, with outer polymer link of

PVA which is added with salt KCl also

increases the mechanical stability and the

absorption.

Figure 2: (a) XRD of sample S3 calcinated (b)

XRD of sample S3 uncalcinated.

AC conductivity

Three samples S1, S2 and S3 membranes of

area 1cm2

with thickness 1mm are taken

between the copper plates of same

dimensions, which hold the samples for the

International Journal of Pure and Applied Mathematics Special Issue

1147

measurement of impedance at different

frequency using Tonghui TH2826 Precision

LCR meter.

International Journal of Pure and Applied Mathematics Special Issue

1148

The ionic conductivity (σ) can be

calculated by the formula

(σ=d/RA)

‘d’ is the distance between the electrodes

which is the thickness of the membrane

and ‘R’ the impedance of the membrane,

that is to be measured for different

frequencies. Also ‘A’ is the area of the

membrane in contact with the copper

plates which is 1cm2.

The conductivity is calculated and the

change in conductivity with frequency is

shown in graph figure 3. The conductivity

increases with increase in frequency.The

presence of KCl nanocrystals in the

membrane increases the conductivity

because of the electron hopping

mechanism. Whereas the increase in

conductivity with increasing frequency is

due to the time taken for polarisation on

the surface of the electrode in contact.

Lower in frequency could increase the

polarisation of the ions on the surface to

electrode where the reversal of polarity at

low frequency need more energy on

opposite charge direction. In the higher

frequencies conduction happens before the

polarisation because of the hopping free

electrons due to addition of impurities. By

the graph in S2 and S3 we can find that

there is increase in conductivity because of

increased salt concentration, from 2 MHz

to 3 MHz and becomes stable after 3 MHz

compared with S1. Hence this concludes

less addition of salt has less conductivity

and the membrane will be an insulator

rather the electrochemical changing which

cannot happen. But when we find below 1

MHz it is find normal and there is only

slight variation of conductivity is obtained

in the doped samples.

Figure 3: AC conductivity of S1, S2 and S3

Linear Sweep Voltammetry

The Electrochemical storage capacity of

the samples S1, S2 and S3 is analysed by

Linear sweep voltammetry [8] measuring

the output current for different voltage

levels (V-I characteristics) using Bio-Logic

Science Instruments SP150 Potentiostat, at

the scan rate of 20 mV/s, each sample is

sandwiched between two stainless steel

electrodes with equal dimensions. The

cathodic and anodic voltage range of less

decomposition occur in sample S1 from -

1V to +1V which are slightly doped with

KCl. The sample S2 and S3 exhibit range

from -1.7V to +1.5V of region of no

decomposition because of addition of

impurities which decreases the dielectric

constant and increases some electron

mobility for electrochemical stability[9].

And also there is a sudden response for

changing in voltage level when compared

to S1. Hence the addition of salt increases

the electrochemical stability of the

membrane [10].

International Journal of Pure and Applied Mathematics Special Issue

1149

Figure 4: LSV of S1, S2 and S3

Cyclic Voltammetry

The activated carbon is prepared from bio

wastes by the chemical activation method using

ZnCl. The mixture of sample solution S3 of

10ml and 5 gram activated carbon is coated in

the aluminium electrodes of 1cm x 1cm. The

prepared electrodes are kept under pressure of

160 mbar for 2 hours after drying it for 1 hour

in 40ºC of temperature without any effect on

polymeric chain. Then the prepared membrane is

kept in between two of the prepared electrodes

by adding some deionised water and kept under

160 mbar of pressure for 1 hour for the

fabrication of EDLC. Then the cell is subjected

to cyclic voltammetry studies [11] using EC-Lab

software and SP150 at the scan

rate of 20 mV/s from 0 to 1.2V. The graph

shows that increase in the potential results in

charging and output current of around 276µA at

maximum and the reversal gives exact

rectangular window of decrease in current which

shows that the charge density stored is high[12]

and the specific capacitance is calculated using

the formula

Cspec= I / (m * Vscan)

Cspec is the specific capacitance value, I is the

average current, m is the mass of the cell and

Vscan is the scan rate. Then ‘m’, the mass of the

cell with two electrodes and the polymeric

membrane embedded is measured as 0.0935

gram. The calculated Cspec is around 2.9518 Fg-1

.

International Journal of Pure and Applied Mathematics Special Issue

1150

Figure 5:CV of S3

Conclusion

The electrochemical stability of the

fabricated membrane is found good and

forms the exact discharge on reversal

because of the high charge density of the

polymer electrolyte even in 10mV/s scan

rate where the wet membrane is bound

exactly with the electrodes fabricated. The

specific capacitance also shows that 2.9518

Fg-1

stands constant for different cycles.

And also the linear sweep voltammetry

shows good electrochemical property and

exhibits the wide range for highly doped

sample than less doped and covers the range

from -1.7V to 1.5V. The AC conductivity

study also proves the increase in

conductivity is because of the addition of

salt which can make some fewer

polarisations on higher frequencies due to

electron hopping mechanism. The structural

studies show higher crystallinity which

occur in highly doped sample S3 also

increasing in porous because of ionic

conductivity in electrospinning which is

added advantage for increasing the

adsorption. Hence the PVA-KCl doped

membrane of exact doping level could be a

suitable one for polymer electrolyte and also

useful for the formation of double layer

capacitance.

International Journal of Pure and Applied Mathematics Special Issue

1151

REFERENCE

[1] Fletchera SI, Sillars FB, Carter RC, Cruden

AJ, Mirzaeian M, Hudson NE, Parkinson JA,

Hall PJ (2010)The effects of temperature on the

performance of electrochemical double layer

capacitors. J Power sources 195:7484-7488

[2] Lepoittevin B, Devalckenaere M, Pantoustier N,

Alexandre M, Kubies D, Calberg C (2002) Poly (ε-

caprolactone)/ clay nanocomposites prepared by melt

intercalation: mechanical, thermal and rheological

properties. Polymer 43:4017-4023

[3] Zhai M, Yoshi F, Kume T (2003) Radiation

modification of starch-based plastic sheets.

Carbohydr polym 52:311-317

[4] Pandey GP, Kumar Y, Hashmi SA,. Ionic liquid

incorporated PEO based polymer electrolyte for

electric double layer capacitors : a comparative study

with lithium and magnesium systems. Solid State

Ionics 2011; 190:93-8

[5] KanbaraT, Inami M, Yamamoto T(1991)New

solid –state electric double-layer capacitor using

polyvinyl alcohol –based polymer solid electrolyte.J

Power Sources 36:87-93

[6] Liew C-W. Ramesh S, Arof AK. A novel approach

on ionic liquid-based poly(vinyl alcohol) proton

conducting polymer electrolytes for fuel cell

applications. Int J Hydrogen Energy 2014; 39:2917-

28

[7] Liew C-W, Ramesh S, Arof AK. Good prospect of

ionic liquid based-poly(vinyl alcohol) proton

conducting polymer electrolytes for supercapacitors

with excellent electrical, electrochemical and thermal

properties. Int J Hydrogen Energy 2014; 39:2953-63

[8]Appetecchi GB, Croce F, Scrosati B (1997) High

performance electrolyte membrane for plastic

Lithium batteries. J Power Sources 66:77

[9]Abidin SZZ, Ali AMM, Hassan OH, Yahya MZA

(2013) Electrochemical studies on cellulose acetate-

LiBOB polymer gel electrolytes. Int J Electrochem

Sci 8:7320-7326

[10]Asmara N, Kufian MZ, Majid SR, Arof AK

(2011) Preparation and characterization of

magnesium ion gel polymer electrolyte for

application in electric double layer

capacitor.Eletrochim Acta 57:91-97

[11]Yin J, Zheng C, Qi L, Wang HY(2011)

Concentrated NaClO4 aqueous solution as promising

electrolytes for electric double layer capacitor. J

Power Sources 196:4080-4087

[12]Meher SK, Justin P, Rao GR (2011) Microwave

mediated synthesis for improved morphology and

psuedocapacitance performance of nickel oxide. ACS

Appl Mater Interfaces 3:2063-2073

International Journal of Pure and Applied Mathematics Special Issue

1152

1153

1154