A doping effect in Mn MOF-74 induced enhanced urea oxidation-assisted hydrogen production

Abstract

During conventional water electrolysis for hydrogen production, the high theoretical potential of the oxygen evolution reaction (OER) leads to excessive energy consumption. In contrast, the urea oxidation reaction (UOR), with its significantly lower theoretical potential, has attracted considerable attention as an energy-efficient alternative for hydrogen production. In this study, we developed a Ni-doped Mn MOF-74 (Ni–Mn MOF-74) catalyst supported on carbon cloth (CC), exhibiting a unique bud-like architecture featuring a petal-surrounded pistil morphology, which exhibits excellent UOR performance in alkaline medium. This catalyst achieves a current density of 100 mA cm⁻² at an ultralow potential of 1.40 V (vs. RHE) in a 1.0 M KOH + 0.5 M urea electrolyte while maintaining remarkable stability. Importantly, in a urea-assisted hydrogen production electrolyzer composed of Ni–Mn MOF-74 (anode) and Pt/C (cathode), the system delivers a current density of 100 mA cm⁻² at a cell voltage of only 1.49 V in alkaline freshwater and 1.50 V in alkaline seawater, respectively, while retaining excellent stability. The enhanced UOR activity stems from Ni doping, which effectively modulates the catalyst's morphology and electronic structure; the synergism of Ni and Mn strengthens the adsorption of urea molecules and OH⁻ ions, thereby accelerating urea decomposition kinetics.