NiOOH/FeOOH Supported on Reduced Graphene Oxide Composite Electrodes for Ethanol Electrooxidation

Composite materials are defined as materials made from two or more constituent materials with different physical or chemical properties, in order to obtain a new property in the developed material. In view of this objective, in this work nickel (Ni) and Ni-Fe alloy microparticles were electrosynthesized at reduction potentials in the range from -0.70 V to -1.20 V (50 mV s^-1) by cyclic voltammetry (CV) onto graphite/paraffin electrode surface modified with nanosheets of reduced graphene oxide (rGO). Previously, the rGO was electrodeposited by CV from a suspension of 1 mg mL^-1 of graphene oxide in PBS solution with pH 9.18, in the potential range from -1.50 V to 0.50 V (10 mV s^-1). After electrodeposition of metals, the oxyhydroxides were formed by CV in an alkaline medium of 0.10 mol L^-1 of NaOH in a potential range of -0.20 V to 1.0 V (100 mV s^-1) with successive scans until stabilization of currents. In order to characterize the developed composite electrodes, the surfaces were investigated by high resolution scanning electron microscopy (FEG-SEM) and energy-dispersive X-ray spectroscopy (EDX). It was observed that NiOOH microparticles had sphere morphologies, while NiOOH/FeOOH had undefined shapes. EDX spectroscopy showed the presence of C, Ni, Fe and O in spectra confirming the formation of oxyhydroxides on the surface of composite electrodes. In order to test the electrochemical performance of the developed composite electrodes, ethanol electrooxidation was carried out in an alkaline medium of 0.10 mol L^-1 of NaOH in the potential range from -0.20 V to 1.0 V (100 mV s^-1) by CV. The electrodes were able to induce the electrooxidation of ethanol at a potential of 0.55 V for the electrode made of NiOOH/FeOOH and around of 0.60 V for the electrode modified with NiOOH.