Tailored Catalytic Microenvironments Enable Efficient Electrochemical Ammonia Production

ABSTRACT 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 (FeFeCoO ₄ ) that enables efficient nitrate‐to‐ammonia reduction (NO ₃ RR). Guided by crystal field and Lewis acid–base principles, Co ^{2 +} substitution induces Jahn–Teller distortions that activate otherwise inert tetrahedral Fe ^{3 +} sites as H* donors. Concurrently, hard–soft acid–base interactions establish decoupled dual‐metal sites: Co ^{2 +} stabilizes nitrogen intermediates, while Fe ^{3 +} forms Fe─O antibonding interactions that facilitate PCET. This ICM directs electron flow, promotes hydrogenation, and suppresses hydrogen evolution. Consequently, FeFeCoO ₄ achieves a peak NH ₃ 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.