Proximity electronic effect of adjacent Ni Site enhances compatibility of hydrogenation and deoxygenation over Cu Site to boost nitrate electroreduction to ammonia

Abstract

Electrocatalytic conversion of nitrate to ammonia (NITRR) can simultaneously achieve the removal of nitrate and the synthesis of value-added ammonia, a promising candidate to replace Haber-Bosch process with low carbon dioxide emissions. However, high hydrogenation energy barrier for *NO intermediates and insufficient supply of active hydrogen cause slow hydrogenation process, and further result in low efficiency of nitrate conversion and ammonia synthesis. Herein, a series of tandem catalysts, one-dimensional coordination polymers (1D CCPs) with dual sites are synthesized and obtained 190.4 mg h^–1 mg_cat^–1 ammonia production rate with Faradaic efficiency of 97.16%, outperforming to the most of recent reported catalysts. The catalytic performances are well-maintained even after a long-term stability test of 1200 h, laying the foundation for practical applications. Density functional theory results reveal that the stationary adsorbed *NO on Ni site induced proximity electronic effect could reduce the energy barrier for hydrogenation of *NO intermediates over Cu site. In addition, the Ni site in the dual sites 1D CCPs is conducive to generating active hydrogen, providing rich proton source to boost the hydrogenation of *NO, and further enhancing the compatibility of deoxygenation and hydrogenation process. Our work paves a new insight into the mechanism of NITRR process and will inspire more research interests in exploring the proximity electronic effect in catalytic process.