Efficient Electroreduction of Nitrate to Ammonia with CuPd Nanoalloy Catalysts

Abstract

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.