Metal–Organic Framework-Derived Zinc–Cobalt Oxide Materials as High-Performance Anodes for Direct Methanol Fuel Cell Application

Abstract

Due to the exhaustion of fossil fuels and rising concerns about environmental pollution, direct methanol fuel cells (DMFCs) have emerged as one of the prominent green energy solutions in recent decades. However, the commercialization of DMFCs faces a significant challenge due to the dependence on expensive noble-metal-based electrode materials and the issue of methanol crossover. Therefore, there has been growing interest in developing cost-effective, high-performance anode catalysts to enhance the methanol oxidation reaction (MOR). In this work, unexplored non-noble transition metal oxide materials, such as metal–organic framework (MOF)-derived ZnO, ZnCo₂O₄, and Zn₂CoO₄, were directly synthesized on Ni foam using a simple solvothermal method, followed by calcination. The MOR activity of all the materials was tested in a 0.5 M methanol solution under alkaline conditions. Due to the synergetic effect of combined metallic composition, mixed metal oxides exhibited superior performance. The order of MOR activity was measured to be ZnO < Zn₂CoO₄ < ZnCo₂O₄. Particularly, ZnCo₂O₄ exhibited the highest mass activity (42.64 mA mg^–1) and geometric current density (166.28 mA cm^–2), outperforming Zn₂CoO₄ (27.44 mA mg^–1) and ZnO (12.72 mA mg^–1). It also demonstrated the lowest onset potential of 1.32 V (vs RHE) compared to Zn₂CoO₄ (1.35 V) and ZnO (1.39 V) and maintained excellent long-term stability for 12 h at 1.5 V (vs RHE). Additionally, to determine the optimal methanol concentration, all electrocatalysts were tested across a range of methanol concentrations from 0.1 to 1 M, showing 0.5 M methanol as the most suitable concentration. This study aims to develop cost-effective MOF-derived electrode materials and optimize methanol concentration to maximize catalytic activity. Furthermore, it establishes a foundation for the development of various MOF-derived electrocatalysts and the advancement of DMFC technology.