Balanced NO x - and Proton Adsorption for Efficient Electrocatalytic NO x - to NH 3 Conversion.

Electrocatalytic nitrate (NO 3 - )/nitrite (NO 2 - ) reduction reaction (eNO x - RR) to ammonia under ambient conditions presents a green and promising alternative to the Haber-Bosch process. Practically available NO x - sources, such as wastewater or plasma-enabled nitrogen oxidation reaction (p-NOR), typically have low NO x - concentrations. Hence, electrocatalyst engineering is important for practical eNO x - RR to obtain both high NH 3 Faradaic efficiency (FE) and high yield rate. Herein, we designed balanced NO x - and proton adsorption by properly introducing Cu sites into the Fe/Fe 2 O 3 electrocatalyst. During the eNO x - RR process, the H adsorption is balanced, and the good NO x - affinity is maintained. As a consequence, the designed Cu-Fe/Fe 2 O 3 catalyst exhibits promising performance, with an average NH 3 FE of ∼98% and an average NH 3 yield rate of 15.66 mg h -1 cm -2 under the low NO 3 - concentration (32.3 mM) of typical industrial wastewater at an applied potential of -0.6 V versus reversible hydrogen electrode (RHE). With low-power direct current p-NOR generated NO x - (23.5 mM) in KOH electrolyte, the Cu-Fe/Fe 2 O 3 catalyst achieves an FE of ∼99% and a yield rate of 15.1 mg h -1 cm -2 for NH 3 production at -0.5 V (vs RHE). The performance achieved in this study exceeds industrialization targets for NH 3 production by exploiting two available low-concentration NO x - sources.