Efficient Electroreduction of Nitrate into Ammonia at Ultralow Concentrations Via an Enrichment Effect

Abstract The electroreduction of nitrate (NO 3 − ) pollutants to ammonia (NH 3 ) offers an alternative approach for both wastewater treatment and NH 3 synthesis. Numerous electrocatalysts have been reported for the electroreduction of NO 3 − to NH 3 , but most of them demonstrate poor performance at ultralow NO 3 − concentrations. In this study, a Cu‐based catalyst for electroreduction of NO 3 − at ultralow concentrations is developed by encapsulating Cu nanoparticles in a porous carbon framework (Cu@C). At −0.3 V vs reversible hydrogen electrode (RHE), Cu@C achieves Faradaic efficiency for NH 3 of 72.0% with 1 × 10 −3 m NO 3 − , which is 3.6 times higher than that of Cu nanoparticles. Notably, at −0.9 V vs RHE, the yield rate of NH 3 for Cu@C is 469.5 µg h −1 cm −2 , which is the highest value reported for electrocatalysts with 1 × 10 −3 m NO 3 − . An investigation of the mechanism reveals that NO 3 − can be concentrated owing to the enrichment effect of the porous carbon framework in Cu@C, thereby facilitating the mass transfer of NO 3 − for efficient electroreduction into NH 3 at ultralow concentrations.