Characterization of electrochemically synthesized PANI on graphite electrode for potential use in electrochemical power sources

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Abstract

Polyaniline (PANI) on graphite electrode was synthesized electrochemically under galvanostatic condition at current density of 2.0 mA cm−2 from aqueous solution of 1.0 mol dm−3 HCl and 0.25 mol dm−3 aniline monomer. Electrochemical characterization of the PANI electrode was performed in 0.5 mol dm−3 HCl using cyclic voltammetry and galvanostatic measurements. The overall charge capacity of the PANI electrode was estimated to be 0.154 mAh cm−2, which corresponds to 25% of the theoretical mass of PANI available for doping exchange. It was observed that during initial cyclization at low pH, the extent of PANI degradation products was insignificant and practically had no influence on the charge/discharge characteristics of the PANI electrode.

Introduction

Electroconducting polymers (ECP) have drawn much attention in last decades, due to their unique properties such: mechanical strength, electrical conductivity, corrosion stability, possibility of chemical and electrochemical synthesis. Such unique properties of ECP were considered in vide area of practical application like: microelectronics, optoelectronics, active corrosion protection, and electrochemical power sources [1].

ECP can be obtained using chemical and electrochemical oxidative synthesis. However, for the some applications electrochemical synthesis without oxidizing species is favorable, permitting the control of the reaction [2]. Electropolymerization can be achieved by different electrochemical techniques such as cyclic voltammetry, potentiostatic or galvanostatic technique. Galvanostatic technique is common for the practical applications, permitting control over some polymerization process parameters regarding the morphology and thickness of the deposit.

Among numerous ECP, polyaniline (PANI) as cathode combined to electronegative metals (mainly zinc) as anode, are the most extensively investigated systems for the application in aqueous based electrochemical power sources [3], [4], [5], [6], [7], [8], [9], [10], [11]. Although these systems are likely to accomplish most of the three E criteria: Energy (high energy content with respect to volume and weight), Economics (low manufacturing and maintenance costs, long service life), Environment (toxic free, safety, low energy consumption, easy to recycle) elaborated by Rüetschi and Beck [12], [13] as the determining factors of an electrochemical power system success, they still have not been commercialized. The main reason is connected to the degradation process of PANI at potentials more positive than 0.5 V. [14], [15].

Electrochemical studies, at the first place cyclic voltammetry, were shown to be particularly useful in investigations of the basic aspects of the polymer growth and degradation mechanisms [16]. Therefore, the aim of this paper was to investigate the influence of the potential on degradation process of electrochemically synthesized PANI electrode in aqueous hydrochloric acid solution, using electrochemical techniques, as a possible electrode material for aqueous based rechargeable power sources.

Section snippets

Experimental

Electrochemical synthesis of PANI on graphite electrode (S = 0.64 cm2) was performed at constant current density of 2 mA cm−2 from aqueous solution of 1.0 mol dm−3 HCl (p.a. Merck) and 0.25 mol dm−3 aniline. Prior to use aniline (p.a. Aldrich) was distilled in argon atmosphere.

The working electrode, cylindrically shaped graphite inserted in Teflon holder was first mechanically polished with fine emery papers (2/0, 3/0 and 4/0, respectively), and than with polishing alumina (1 μm, Banner Scientific Ltd.)

Results and discussion

Aniline electropolymerization on graphite electrode from 1.0 mol dm−3 HCl and 0.25 mol dm−3 aniline at constant current density of 2.0 mA cm−2 during 1080 s is given in insert of Fig. 1. Electrochemical polymerization of aniline occurs together with insertion of chloride ions (doping) according to the equation:(PANI)n + nyCl  [PANIy+(Cl)]n + nyewhere y is doping degree, defined as ratio between the number of charges in the polymer and the number of monomer units.

In order to investigate the influence of

Conclusion

Electrochemical polymerization of PANI on graphite electrode from aqueous solution of 1.0 mol dm−3 HCl containing 0.25 mol dm−3 aniline was successively performed galvanostatatically from solution of hydrochloric acid containing aniline. The determined overall charge capacity of the PANI electrode in stationary state conditions was 0.154 mAh cm−2. The active mass of the PANI electrode was calculated to be 25% of the overall polymerized mass, meaning that only 25% of the mass was available for the

Acknowledgment

This work is financially supported by the Ministry of Science, Republic of Serbia, No. 142044.

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