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PREPARATION OF POLYANILINE/Ru-OXIDE COMPOSITE FOR ELECTROCHEMICAL SUPERCAPACITORS

It has already been found that owing to high specific capacitance, high reversibility, wide potential range and very good cycleability, hydrous Ru-oxide is one of the best materials for electrochemical supercapacitors [1]. However, electrochemical reactions giving rise to its high pseudocapacitance are limited to a rather thin surface layer of deposited film. It is therefore of high importance to improve utilization of Ru material and achieve higher gravimetric energy and power densities. Among various strategies for preparation of hydrous Ru-oxide electrode with enhanced capacitance, formation of different composite materials has already been attempted in the literature [2-4]. Such composites are synthesized in order to combine beneficial properties of hydrous Ru-oxide with advantages of other materials such as high surface area. Due to the extremely high surface area and charge storage capability, conducting polymers are already found as promising candidates for formation of composite with Ru-oxide. In this work, different methods of polyaniline (PANI)/Ru-oxide composite preparation at glassy carbon (GC) electrodes are reported. NafionTM was introduced as a template for PANI growth and for improving mechanical properties of electrodes. The results are compared with PANI/Ru-oxide composite prepared at Pt electrodes without the NafionTM. The electrochemical behaviour of prepared composites were characterized in H2SO4 acid solution by cyclic voltammetry and electrochemical impedance spectroscopy techniques. Two different procedures (Methods A and B) for preparation of PANI/Ru-oxide composites are developed and described as follows: Method A (four-step procedure): i) Nafion layer was casted onto GC electrode and left overnight for evaporation of solvent ; ii) PANI matrix was formed potentiodynamically within NafionTM matrix from aniline/H2SO4 solution at defined scan rate and different number of cycles ; iii) Ru was electrodeposited onto PANI matrix by the potential square wave method from RuCl3/HCl electrolyte solution ; iv) deposited Ru was oxidised to hydrous Ru-oxide in H2SO4 solution by cycling the potential within strongly defined potential limits and scan rate. Method B: (two-step procedure): i) Suspension of Nafion and Ru-oxide was casted onto GC electrode and left overnight for evaporation of solvent. ii) PANI films were formed within the pores of Nafion/Ru-oxide as in Method A. Cyclic voltammograms of Pt/PANI and Pt/PANI/Ru-oxide electrodes are in 0.5 mol dm-3 H2SO4 solution at scan rate 50 mV s-1 are shown in Fig. 1. Cyclic voltammograms of GC/Nafion/PANI and GC/Nafion/PANI/Ru-oxide electrodes prepared by Methods A and B in the same solution and scan rate are shown in Figs. 2 and 3, respectively. The results demonstrate that both methods lead to the overall increase of specific charges of composite electrodes. This is particularly prominent for the composite prepared by the Method A where additionally, a widening of the voltage range of capacitive response is observed (Figs.1-2). Increase of the overall charge is observed also for the composite prepared by the Method B, except for thicker PANI4 deposits, where irreversible damages to the electrodes are observed through deformation of volatammograms (Fig.3). Further experimental investigations related to varying the amounts of Ru-oxide and PANI and other details of preparation procedures are currently in a progress.

Polyaniline; Ru-oxide; Nafion; Supercapacitors

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