Efficient tandem electrochemical reduction of nitrate to ammonia through coupling Co2P with Co/Co2P interface

Abstract

Electrochemical nitrate reduction reaction (NO3− RR) is a highly attractive route for both ammonia (NH3) synthesis and wastewater treatment. The NO3− RR involves the reduction of NO3− to NO2−, the conversion of NO2− to NH3, and the dissociation of H2O to *H. However, these three reactions depend on distinct catalyst properties that are difficult to achieve in a single-site catalyst. Here a tandem catalyst of Co/Co2P heterostructures encapsulated by N-doped graphene shells on carbon nanotube (Co/Co2P@NG/CNT) for NO3− RR were developed, achieving an attractive NH3 yield rate of 47.8 mg h−1 mg−1 with a corresponding NH3 Faradaic efficiency of 99.2% in 0.05 mol/L NO3− solution, exceeding most of the reported catalysts under the same NO3− concentration. Experimental and theoretical studies reveal that the Co2P effectively reduces NO3− to NO2−, while Co/Co2P interface is responsible for the subsequent conversion of NO2− to NH3. Meanwhile, the H2O dissociation is promoted by the Co/Co2P interface to generate *H for intermediates hydrogenation. Such a tandem catalysis process accelerates the conversion of NO3− into NH3. The Co/Co2P@NG/CNT also shows good stability due to the robust protection from N-doped graphene shell.