Graphene accelerates electron transfer over copper-cobalt nanoparticles for efficient electroreduction of nitrate to ammonia

Nitrate sewage will give rise to the hazarding of aquatic ecosystems and human life. Electrochemical reduction of nitrate to ammonia (NO 3 -RR) was reckoned as the prospective pathway for ecological remediation and nitrogen cycle but faced with challenges. In this work, through decorating graphene on copper-cobalt (CuCo) nanoparticles, the electron transferring between Co and Cu is intensified, which is conducive to NO 3 -RR. The optimized catalyst (CuCo-Gr0.1) performs eminent ammonia yield of 0.29 mmol h -1 cm -2 with Faradic efficiency (FE) of 97.2 % at -0.16 V versus reversible hydrogen electrode (vs RHE) and increasing to 0.91 mmol h -1 cm -2 at -0.56 V vs RHE in acid electrolyte. Besides, CuCo-Gr0.1 also exhibits high performance for the reduction of nitrate to ammonia in neutral condition, which can combine with uranyl ions to produce ammonium uranium oxide hydrate. The density functional theory calculations reveal that the decorated graphene on CuCo can promote electron transfer and NO 3 -adsorption, thus accelerating the catalytic kinetics of NO 3 - RR. This work provides new insights into the design of efficient NO 3 -RR electrocatalyst for nitrogen and uranium cycling in nuclear industry wastewater treatment.