Composite electrodes with superior catalytic activity in methanol electro-oxidation fabricated using ternary NiO–CuO–ZnO mixed metal oxides

Abstract

There is a vital need to develop cheaper catalysts as alternatives to expensive platinum, gold, and palladium precious-metal catalysts and to overcome the limitations caused by carbon monoxide poisoning in direct methanol fuel cells (DMFCs). In the present work, a single-step hydrothermal method has been utilized for the synthesis of a NiO–CuO–ZnO(NCZ) ternary mixed metal oxide composite and binary NiO–CuO (NC), CuO–ZnO (CZ), and NiO–ZnO (NZ) composites for optical and fuel cell applications. UV spectroscopy analysis reveals energy band gaps of binary and ternary mixed metal oxides of Ni, Cu, and Zn via Tauc plots. In a basic medium (0.5 M NaOH) at a potential of +0.29 V (vs. Ag|AgCl), the NCZ ternary mixed metal oxide composite displayed 1.34-, 2- and 3.9-times greater methanol (MeOH) oxidation activity compared to binary NiO–ZnO (NZ) (5.8 mA cm⁻²), CuO–ZnO (CZ) (3.9 mA cm⁻²) and NiO–CuO (NC) (2.0 mA cm⁻²) composites, respectively. The tertiary metal oxide catalyst has a high oxidation activity due to the synergistic effect of metal oxides in NCZ. NiO provides active sites for the electrooxidation of methanol, while CuO and ZnO contribute to the excellent chemical and mechanical stability of the prepared electrocatalyst. Various electrochemical features of the NCZ electrode, like surface area, durability and peak current values, are found to be good in an alkaline medium as compared to an acidic medium. The charge transfer resistance, electron recombination lifetime, and peak frequency values are determined using electrochemical impedance spectroscopy (EIS) and Nyquist and Bode plots. The NCZ electrocatalyst exhibits superior performance to binary catalysts, making it a cost-effective, efficient, non-noble metal-containing, and eco-friendly candidate for energy and optoelectronic devices.