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

Electrochemical nitrate reduction reaction (eNORR) to ammonia (NH) holds great promise for the green treatment of NO and ambient NH synthesis. Although Fe-based electrocatalysts have emerged as promising alternatives, their excellent eNORR-to-NH 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 CoFe electrocatalyst for efficient eNORR-to-NH activity in neutral media, which breaks down the conventional pH-dependent kinetics restrictions and shows a 98.6% NH Faradaic efficiency (FE) and 99.9% NH selectivity at -0.69 V vs RHE. The synergetic Co-Fe dual sites were demonstrated to enable the optimal free energies of eNORR-to-NH species and balance water dissociation and protonation of adsorbed NO. Notably, the CoFe electrocatalysts can attain a high current density of 100 mA cm with a high NH FE surpassing 96% and long-term stability for over 500 h eNORR-to-NH 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 eNORR-to-NH and thus avoids alkaline electrolytes and noble metals for practical sustainable nitrate upcycling technology.