Self-Triggering a Locally Alkaline Microenvironment of Co4Fe6 for Highly Efficient Neutral Ammonia Electrosynthesis

Electrochemical nitrate reduction reaction (eNO₃^-RR) to ammonia (NH₃) holds great promise for the green treatment of NO₃^- and ambient NH₃ synthesis. Although Fe-based electrocatalysts have emerged as promising alternatives, their excellent eNO₃^-RR-to-NH₃ activity is usually limited to harsh alkaline electrolytes or alloying noble metals with Fe in sustainable neutral electrolytes. Herein, we demonstrate an unusual self-triggering localized alkalinity of the Co₄Fe₆ electrocatalyst for efficient eNO₃^-RR-to-NH₃ activity in neutral media, which breaks down the conventional pH-dependent kinetics restrictions and shows a 98.6% NH₃ Faradaic efficiency (FE) and 99.9% NH₃ selectivity at -0.69 V vs RHE. The synergetic Co-Fe dual sites were demonstrated to enable the optimal free energies of eNO₃^-RR-to-NH₃ species and balance water dissociation and protonation of adsorbed NO₂^-. Notably, the Co₄Fe₆ electrocatalysts can attain a high current density of 100 mA cm^-2 with a high NH₃ FE surpassing 96% and long-term stability for over 500 h eNO₃^-RR-to-NH₃ in a membrane electrode assembly (MEA) electrolyzer. This work provides insight into tailoring the self-reinforced local-alkalinity on the Fe-based alloy electrocatalysts for eNO₃^-RR-to-NH₃ and thus avoids alkaline electrolytes and noble metals for practical sustainable nitrate upcycling technology.