Insights into the electro-oxidation of hydrazine at single-walled carbon-nanotube-modified edge-plane pyrolytic graphite electrodes electro-decorated with metal and metal oxide films

Abstract

Electrochemistry of edge-plane pyrolytic graphite electrodes (EPPGEs) modified with Aldrich single-walled carbon nanotubes (SWCNTs) electro-decorated with metal (Ni, Fe and Co) and their oxides have been studied. The morphology and identity of the metallic dispersions were examined by scanning electron microscopy and energy-dispersive spectroscopy. We show that SWCNTs serve as efficient conducting carbon material for electronic communication between metal films and the underlying carbon electrode. By using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques, it is proved that both EPPGE-SWCNT-Ni and EPPGE-SWCNT-Fe exhibit comparable electrochemical response in buffered aqueous solution (pH 7.0) and towards electro-oxidation of hydrazine in Na2SO4 solution. The impedance spectra of these SWCNT-metal hybrids were complicated and follow electrical equivalent circuit model typical of adsorption-controlled charge transfer kinetics. Hydrazine impedance spectra exhibited inductive loop, characteristic of Faradaic current being governed by the occupation of an intermediate state. On the other hand, the EIS data obtained in a simple redox probe, [Fe(CN)6]3−/[Fe(CN)6]4−, showed that EPPGE-SWCNT and EPPGE-SWCNT-Ni followed electrical equivalent circuit models typical of partial charge transfer or adsorption-controlled kinetics with some resemblance to the behaviour of electrolyte–insulator–semiconductor sensors.