Engineering Metal-to-Metal Charge Transfer in Bimetallic CoFe-MOF-74 for Efficient Solar-Driven Photocatalytic Nitrogen Fixation

Bimetallic engineering in metal−organic frameworks (MOFs) offers a powerful strategy to enhance photocatalytic nitrogen fixation by optimizing electronic structure and facilitating directional charge transfer. This work reports a rational design of CoM-MOF-74 (M = Fe, Cd, Mg) catalysts synthesized via a solvothermal method. Among them, CoFe0.25-MOF-74 (Co:Fe = 4:1) microrods deliver the best performance, achieving an ammonia production rate of 120 μmol gcat−1 h−1 with an apparent quantum efficiency of 1.63% at 420 nm. The catalyst sustains high activity under outdoor sunlight and remains effective in multiple water environments. Mechanistic studies reveal that Fe incorporation alters the coordination environment while enabling synergistic Fe→Co charge transfer. This cooperative effect strengthens N2 activation at the neighboring Co sites and concurrently suppresses the competing hydrogen evolution reaction. This work highlights metal-to-metal charge transfer in MOFs as a fundamental strategy for constructing efficient and durable photocatalysts for solar-driven ammonia synthesis.