Tailored Catalytic Microenvironments Enable Efficient Electrochemical Ammonia Production

Multi-electron hydrogenation reactions are central to sustainable energy and nitrogen cycling but require catalysts with precise proton-coupled electron transfer (PCET) and intermediate control. Here we report an integrated catalytic microenvironment (ICM) in a Co-substituted inverse spinel oxide (FeFeCoO4) that enables efficient nitrate-to-ammonia reduction (NO3RR). Guided by crystal field and Lewis acid-base principles, Co2 + substitution induces Jahn-Teller distortions that activate otherwise inert tetrahedral Fe3 + sites as H* donors. Concurrently, hard-soft acid-base interactions establish decoupled dual-metal sites: Co2 + stabilizes nitrogen intermediates, while Fe3 + forms Fe─O antibonding interactions that facilitate PCET. This ICM directs electron flow, promotes hydrogenation, and suppresses hydrogen evolution. Consequently, FeFeCoO4 achieves a peak NH3 yield of 1.89 × 10- 6 mol s- 1 cm- 2 with 96.6% Faradaic efficiency and 30.5% energy efficiency, and stable operation at 0.5 A cm- 2 for 265 h. This strategy offers a blueprint for catalysts for multi-electron hydrogenations beyond nitrate reduction.