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.