Green and inexpensive CuS/S-RGO nanoflowers efficiently electrochemically reduce CO₂and NO₃⁻to produce urea

Electrochemical reduction using greenhouse gas CO₂ and environmental pollutant NO₃⁻as feedstocks under ambient temperature has emerged as a desirable approach for urea synthesis. To date, the method of electrocatalytic urea synthesis still suffers from considerable limitations, such as insufficient catalyst activity and severe side reactions. Therefore, there is an urgent need to design a highly efficient and selective catalyst for CN coupling. In this work, a CuS/S-RGO composite catalyst was prepared via a simple and green two-step hydrothermal method, where CuS nanoflowers are uniformly dispersed on the sulfur-doped three-dimensional reduced graphene oxide (S-RGO) support. CuS/S-RGO possesses a unique microporous structure, which is beneficial for exposing active sites and enhancing stability. The electronic configuration of Cu and the doping of S promote the occurrence of CN coupling reactions. When applied to the system of electrochemical reduction for urea production, this electrocatalyst exhibits the highest urea formation rate and Faraday efficiency of 10.85 mmol^.h^-1.g⁻¹and 45.95 %, respectively, at −0.7 V (vs. RHE). This study represents the first application of a composite electrocatalyst combining copper-based sulfides with sulfur-doped graphene in the system of electroreduction of CO₂ and NO₃⁻for urea synthesis, and it demonstrates favorable electrocatalytic activity.