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

Abstract

Nitrate sewage and energy-intensive ammonia synthesis threaten both health and the ecosystem. Electrocatalytic nitrate reduction reaction (NO₃⁻RR) can simultaneously address both these plights. Here, graphene was wrapped around a CuCo nanoparticle (CuCo–Gr0.1). Graphene accelerated Cu-to-Co electron transfer and charge redistribution, thereby enhancing NO₃⁻RR. The optimized CuCo–Gr0.1 exhibited excellent NO₃⁻RR performance, with an NH₃ yield rate of 0.29 mmol h⁻¹ cm⁻² and a faradaic efficiency (FE) of 97.2% at −0.16 V versus the reversible hydrogen electrode (RHE) in 0.5 M HNO₃. Combined with theoretical calculations, the results revealed that enhanced electron transfer strengthened nitrate adsorption, facilitated deoxygenation and hydrogenation, and lowered the energy barrier, thereby accelerating the catalytic kinetics. Additionally, CuCo–Gr0.1 demonstrated high NO₃⁻RR performance in neutral conditions and was capable of co-reducing uranyl ions (UO₂²⁺) to ammonium uranium oxide hydrate. This work provides new insights into the design of efficient electrocatalysts for nitrogen and uranium cycling in nuclear industry wastewater treatment.