Efficient Electroreduction of Nitrate to Ammonia with CuPd Nanoalloy Catalysts

The electroreduction of nitrate (NO₃ ^- ) to valuable ammonia (NH₃ ) is a green and appealing alternative to the Haber-Bosch process. Nevertheless, this process suffers from low performance for NH₃ due to the sluggish multi-electron/proton-involved steps. In this work, a CuPd nanoalloy catalyst was developed toward NO₃ ^- electroreduction at ambient conditions. By modulating the atomic ratio of Cu to Pd, the hydrogenation steps of NH₃ synthesis during NO₃ ^- electroreduction can be effectively controlled. At -0.7 V versus reversible hydrogen electrode (vs. RHE), the optimized CuPd electrocatalysts achieved a Faradaic efficiency for NH₃ of 95.5 %, which was 1.3 and 1.8 times higher than that of Cu and Pd, respectively. Notably, at -0.9 V vs. RHE, the CuPd electrocatalysts showed a high yield rate of 36.2 mg h^-1  cm^-2 for NH₃ with a corresponding partial current density of -430.6 mA cm^-2 . Mechanism investigation revealed the enhanced performance originated from the synergistic catalytic cooperation between Cu and Pd sites. The H-atoms adsorbed on the Pd sites prefer to transfer to adjacent nitrogen intermediates adsorbed on the Cu sites, thereby promoting the hydrogenation of intermediates and the formation of NH₃ .