2D Polymeric N-Heterocyclic Carbene Copper Microsheets Enable Tandem Electroreduction of Nitrate to Ammonia

Electrochemical nitrate reduction into ammonia represents a sustainable route for ammonia production, simultaneously contributing to the alleviation of water pollution. However, achieving a high yield rate and selectivity for ammonia remains a challenge for Cu-based catalysts owing to the accumulation of competing nitrite. Herein, 2D polymeric N-heterocyclic carbene copper microsheets are designed as tandem catalysts, with polymeric microsheets acting as tandem substrates to robustly anchor copper sites through N-heterocyclic carbene. In this tandem catalyst, the reduction of nitrate to nitrite preferentially occurred at the copper sites. The resultant nitrite is concurrently adsorbed by polymeric microsheets, which in turn promotes its conversion kinetics into ammonia, thus minimizing the formation of nitrite byproducts. As a result, this tandem catalyst demonstrates an ammonia yield rate of 23.4 mg h⁻¹ cm⁻², along with a Faradaic efficiency of 97% for ammonia, while maintaining stable performance throughout 30 consecutive cycles and 55 h of chronoamperometric operation. This work showcases the potential of polymeric N-heterocyclic carbene as a novel class of tandem substrate for ammonia production and offers a polymeric platform for nitrate valorization and water purification.