Nitrite Electroreduction to Ammonia Promoted by Molecular Carbon Dioxide with Near‐unity Faradaic Efficiency

Abstract Electrochemical reduction of nitrite (NO 2 − ) offers an energy‐efficient route for ammonia (NH 3 ) synthesis and reduction of the level of nitrite, which is one of the major pollutants in water. However, the near 100 % Faradaic efficiency (FE) has yet to be achieved due to the complicated reduction route with several intermediates. Here, we report that carbon dioxide (CO 2 ) can enhance the nitrite electroreduction to ammonia on copper nanowire (Cu NW) catalysts. In a broad potential range (−0.7∼−1.3 V vs. RHE), the FE of nitrite to ammonia is close to 100 % with a 3.5‐fold increase in activity compared to that obtained without CO 2. In situ Raman spectroscopy and density functional theory (DFT) calculations indicate that CO 2 acts as a catalyst to facilitate the *NO to *N step, which is the rate determining step for ammonia synthesis. The promotion effect of CO 2 can be expanded to electroreduction of other nitro‐compounds, such as nitrate to ammonia and nitrobenzene to aniline.