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

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.