In situ grown Fe₃O₄ particle on stainless steel: A highly efficient electrocatalyst for nitrate reduction to ammonia

NH₃ is an essential feedstock for fertilizer synthesis. Industry-scale NH₃ synthesis mostly relies on the Haber–Bosch method, however, which suffers from massive CO₂ emission and high energy consumption. Electrocatalytic NO₃^– reduction is an attractive substitute to the Haber–Bosch method for synthesizing NH₃ under mild conditions. As this reaction will produce a variety of products, it highly desires efficient and selective electrocatalyst for NH₃ generation. Here, we report in situ grown Fe₃O₄ particle on stainless steel (Fe₃O₄/SS) as a high-efficiency electrocatalyst for NO₃^– reduction to NH₃. In 0.1 M NaOH with 0.1 M NaNO₃, such Fe₃O₄/SS reaches a remarkable Faradaic efficiency of 91.5% and a high NH₃ yield of 10,145 μg·h^–1·cm^–2 at –0.5 V vs. reversible hydrogen electrode (RHE). Furthermore, it owns robust structural and electrochemical stability. This work provides useful guidelines to expand the scope of metallic oxide electrocatalysts for NH₃ synthesis. The catalytic mechanism is uncovered and discussed further by theoretical calculations.