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

Abstract

The electroreduction of nitrate (NO₃ ^- ) pollutants to ammonia (NH₃ ) offers an alternative approach for both wastewater treatment and NH₃ synthesis. Numerous electrocatalysts have been reported for the electroreduction of NO₃ ^- to NH₃ , but most of them demonstrate poor performance at ultralow NO₃ ^- concentrations. In this study, a Cu-based catalyst for electroreduction of NO₃ ^- 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 NH₃ of 72.0% with 1 × 10^-3 m NO₃ ^- , which is 3.6 times higher than that of Cu nanoparticles. Notably, at -0.9 V vs RHE, the yield rate of NH₃ for Cu@C is 469.5 µg h^-1 cm^-2 , which is the highest value reported for electrocatalysts with 1 × 10^-3 m NO₃ ^- . An investigation of the mechanism reveals that NO₃ ^- can be concentrated owing to the enrichment effect of the porous carbon framework in Cu@C, thereby facilitating the mass transfer of NO₃ ^- for efficient electroreduction into NH₃ at ultralow concentrations.