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.