Preparation of Ni-metal oxide nanocomposites and their role in enhancing the electro-catalytic activity towards methanol and ethanol

Abstract

Ni–metal oxide (Fe2O3, ZnO, Co3O4 and MnO2) nanocomposites were synthesized on carbon substrates by electrodeposition technique. These catalysts were tested as anodes for electrooxidation of both methanol and ethanol. To study the chemical composition of the deposits, energy dispersive X-ray spectroscopy (EDX) was used and the maximum wt% of metal oxides in the prepared composites was found to be 11.4, 11.7, 9.3 and 3.8 for Fe2O3, ZnO, MnO2 and Co3O4, respectively. The morphology of the catalysts surface is significantly affected by the existence of metal oxides as confirmed by scanning electron microscope (SEM) images. The phase structure and the particle size of the catalysts were recognized from X-ray diffraction (XRD). A reduction in the Ni grains was seen in the matrix of the composites compared with that of Ni/C. Cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) were employed to study the electrocatalytic activity of the prepared nanocomposites. All the results displayed a satisfactory electrocatalytic activity, better stability, lower charge transfer resistance, and stronger resistance to the poisoning of the nanocomposites compared with that of Ni/C. A synergistic effect among multiple active sites due to the presence of mixed oxides for the nanocomposites could enhance their electrocatalytic activity. The performance of the different prepared catalysts towards the electrooxidation process was established in the order of: Ni–Fe2O3/C > Ni–ZnO/C > Ni–Co3O4/C > Ni–MnO2/C > Ni/C. Ni–metal oxide nanocomposites appeared to be promising and less expensive anode catalysts for fuel cell applications.