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.