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

Abstract

In this work, nickel (Ni) and Ni-Fe bimetallic 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 the potential range from −0.20 V to 1.0 V (100 mV s−1) with successive scans until stabilization of currents. In order to characterize the developed electrodes composites, the surfaces were investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Electrochemical performance of the developed electrodes composites to 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.

Electrocatalysis of Ethanol and Methanol Electrooxidation by Composite Electrodes with NiOOH/FeOOH Supported on Reduced Graphene Oxide onto Composite Electrodes

“…The mixture of the two did not presented defined shapes, only undefined features. The same situation was reported by Oliveira and collaborators [12,13], but the presence of NiOOH and FeOOH was confirmed by EDX and mapping of elements on the surface of the electrodes.…”

“…Figure 2B shown the cyclic voltammograms of the EC/rGO/NiOOH-FeOOH electrode in the absence and presence of 10 mmol L -1 of methanol and ethanol, the electrode showed an oxidation peak at the potential of 0.57 V for both alcohols and the electrochemical behavior was similar to composite electrode modified with NiOOH. With the addition of FeOOH, the electrodes showed a similar electrocatalytic process of ethanol and methanol in relation to the EC/rGO/NiOOH, however it was observed a shifting in the oxidation potential of ethanol and methanol to a more negative potential, in this case from ~0.66 V to ~0.57 V. Oliveira and collaborators [12] showed that the electrodes modified with only FeOOH in alkaline medium does not shown a electrocatalytic current at the studied potential in presence of alcohols. However, Qiu and collaborators [18] observed that electrodes modified with only FeOOH have a redox potential between −0.60 V and −1.20 V and that the addition of FeOOH can reduce the electrochemical oxidation of Ni(OH)2 in NiOOH, due to the decrease in the amount of active Ni site on the surface, thus the decrease in the amount of electrons transferred by the Ni atom can also be altered.…”

“…As described in the literature [11,12], the electrodes (EC) were prepared by inserting the graphite and paraffin composite into a plastic syringe and connected to a copper wire. After making, the electrodes were polished with sandpapers 1200 and 4000 until there was a clear and homogeneous surface.…”

“…The electrodeposition of Ni and Fe oxyhydroxide (NiOOH and FeOOH) on reduced graphene oxide (rGO) nanosheets was performed similar to the literature: [12,14]. The electrodeposition of graphene oxide was made by CV with 10 successive potential cycles in the potential range from -1.50 V to 0.50 V (vs. Ag/AgCl) at 10 mV s -1 in dispersion 1 mg mL -1 of GO in phosphate buffer solution (pH 9.00) with magnetic stirring.…”

“…After electrodeposition of the rGO, deposition of iron and nickel was performed as described elsewhere [12]. Fe and Ni were electrodeposited by CV during 25 successive scans of potential from −0.70 V to −1.20 V (vs. Ag/AgCl) at 50 mV s -1 in a solution of 1.0 mol L -1 of FeSO4 and 5.0 mmol L -1 of NiCl2.…”