Pulsed Nitrate-to-Ammonia Electroreduction Facilitated by Tandem Catalysis of Nitrite Intermediates

Electroreduction of nitrate to ammonia offers a promising pathway for nutrient recycling and recovery from wastewater with energy and environmental sustainability. There have been considerable efforts on the regulation of reaction pathways to facilitate nitrate-to-ammonia conversion over the competing hydrogen evolution reaction but only with limited success. Here, we report a Cu single-atom gel (Cu SAG) electrocatalyst that produces NH₃ from both nitrate and nitrite under neutral conditions. Given the unique mechanism of NO₂^- activation on Cu SAGs with spatial confinement and strengthened kinetics, a pulse electrolysis strategy is presented to cascade the accumulation and conversion of NO₂^- intermediates during NO₃^- reduction with the prohibited competition from the hydrogen evolution reaction, thus substantially enhancing the Faradaic efficiency and the yield rate for ammonia production compared with constant potential electrolysis. This work underlines the cooperative approach of the pulse electrolysis and SAGs with three-dimensional (3D) framework structures for highly efficient nitrate-to-ammonia conversion enabled by tandem catalysis of unfavorable intermediates.