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 threedimensional (3D) framework structures for highly efficient nitrate-to-ammonia conversion enabled by tandem catalysis of unfavorable intermediates.

Automated summary

Electroreduction of nitrate to ammonia provides a promising approach for nutrient recycling and recovery from wastewater while ensuring energy and environmental sustainability. By utilizing a pulse electrolysis strategy and a Cu single-atom gel (Cu SAG) catalyst, ammonia production from nitrate and nitrite under neutral conditions is achieved with significantly enhanced Faradaic efficiency and yield rate compared to constant potential electrolysis. This work highlights the synergistic effect of pulse electrolysis and Cu SAGs with three-dimensional framework structures for efficient conversion of nitrate to ammonia through tandem catalysis of unfavorable intermediates.