Coupled spin-coordination self-adaptation drives efficient nitrate to ammonia conversion

Abstract Electrochemical nitrate reduction reaction (NO 3 RR) is a promising approach for sustainable ammonia production and nitrogen pollution mitigation, but its efficiency is often limited by sluggish nitrate hydrogenation. The spin state and coordination environment of the active metal play crucial roles in selectivity and reaction kinetics, yet designing electronically adaptive active sites for the complex multielectron NO 3 RR process remains challenging. Here, we report an Fe-N 3 (PO X ) single-atom catalyst that breaks the local symmetry to induce a switch-like adaptive coordination and dynamical tuning of the Fe spin state, enabling high activity at low overpotentials, with an ammonia yield rate of 21.96 g mg Fe −1 h −1 and a Faradaic efficiency of 89.8% at −0.56 V versus the reversible hydrogen electrode (RHE). In situ spectroscopy confirms coordination reorganization and an increase in the Fe spin state, accompanied by accelerated consumption of asymmetric nitrate species. The resulting higher spin state character enhances back-donation into nitrate-derived intermediates and accelerates hydrogenation. This study demonstrates a viable strategy to manipulate spin states at the single-atom level, providing mechanistic insight for optimizing ammonia production on Fe-based catalysts.