Enhancing Electrochemical Nitrate Reduction to Ammonia over Cu Nanosheets via Facet Tandem Catalysis

Electrochemical conversion of nitrate (NO3−) into ammonia (NH3) represents a potential way for achieving carbon−free NH3 production while balancing the nitrogen cycle. Herein we report a high−performance Cu nanosheets catalyst which delivers a NH3 partial current density of 665 mA cm−2 and NH3 yield rate of 1.41 mmol h−1 cm−2 in a flow cell at −0.59 V vs. reversible hydrogen electrode. The catalyst showed a high stability for 700 h with NH3 Faradaic efficiency of ~88% at 365 mA cm−2. In situ spectroscopy results verify that Cu nanosheets are in situ derived from the as-prepared CuO nanosheets under electrochemical NO3− reduction reaction conditions. Electrochemical measurements and density functional theory calculations indicate that the high performance is attributed to the tandem interaction of Cu(100) and Cu(111) facets. The NO2− generated on the Cu(100) facets is subsequently hydrogenated on the Cu(111) facets, thus the tandem catalysis promotes the crucial hydrogenation of *NO to *NOH for NH3 production.