Preparation, characterization and bifunctional catalytic properties of MOF(Fe/Co) catalyst for oxygen reduction/evolution reactions in alkaline electrolyte

A mixed metal–ion metal–organic framework (MOF(Fe/Co)) was synthesized by a hydrothermal process using ferric and cobalt salts as the metal–ion precursors and trimesic acid as the organic ligand. The structure of the as-prepared MOF(Fe/Co) was characterized by X-ray diffraction (XRD), N2 adsorption–desorption, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetry/differential thermogravimetry (TG/DTG). The bifunctional catalytic activities of MOF(Fe/Co) toward the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) in alkaline electrolyte were investigated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The results demonstrate that the as-prepared MOF(Fe/Co) has a good crystalline structure with abundant micropores, a high specific surface area and a high thermal stability. The MOF(Fe/Co) exhibits excellent bifunctional catalytic activities for OER and ORR. The high specific surface area and abundant micropores are beneficial for oxygen diffusion and catalytic sites utilization in the catalyst, which is favorable for the OER and ORR. The RDE results for MOF(Fe/Co)-catalyzed ORR indicate that the two-electron pathway was preferred at relatively positive potentials, whereas the four-electron pathway gradually dominated at more negative potentials.