Ultrasonically Engineered Low‐Coordination Mn Sites in Fe‐MOF Promote Charge Separation for Sacrificial‐Agent‐Free Photocatalytic N 2 Reduction

Photocatalytic nitrogen reduction involves complex proton‐coupled multi‐electron transfer processes, which bring about abundant reaction pathways and thus result in poorly controllable product selectivity. Benefiting from their unique electronic configuration and unsaturated coordination environment, single‐atom photocatalysts can effectively regulate the reaction pathways of photoreductive N 2 activation and reduction, thereby improving the selectivity and NH 3 productivity of target ammonia products. Herein, an acetate‐modified ultrasonication method is developed to construct atomically dispersed, coordinatively unsaturated Mn–N sites on Fe‐based metal–organic frameworks (FeMOFs). Distinct from traditional carbon‐based single‐atom catalysts, these Mn─N sites are fabricated via a mild wet‐chemistry approach without high‐temperature treatment. The optimized U‐FeMnMOF(Fe:Mn = 1:3) achieves a high NH 3 productivity of 1823.1 µmol·g −1 ·h −1 , 21.2 times that of pure FeMOF. Characterizations and DFT results verify that Mn─N sites not only activate N 2 and optimize hydrogen adsorption, but also work as a charge transfer mediator to form a direct Z‐scheme heterojunction. This study presents a feasible strategy to synthesize non‐carbon M─N single‐atom catalysts for efficient PNRR.