Highly selective electrochemical urea synthesis via C-N coupling from CO₂ and nitrate reduction on Cu₂S/CuS catalyst

Electrochemical urea synthesis through the CO₂ and nitrate reduction reaction is a promising sustainable alternative, but it is limited by inefficient C-N coupling and competing hydrogen evolution. Here, we report a sulfur-modulated Cu₂S/CuS electrocatalyst that promotes selective urea formation by tuning the adsorption of key intermediates. The catalyst achieves a urea yield of 260.8 ± 10.2 μg h⁻¹ cm⁻² with a remarkable faradaic efficiency of 80.0 ± 2.8% at −0.4 V versus RHE for a Cu-S-based catalyst. In situ FT-IR spectroscopy identifies *CO and *NO intermediates along with a C-N stretching signal, while isotopic HRMS confirms nitrate-derived nitrogen in the product. These results support a mechanism in which sulfur-modulated Cu^δ+-S sites enhance *CO-*NO coupling while suppressing hydrogen evolution (HER). This work highlights sulfur incorporation as an effective strategy to regulate intermediate adsorption and enable selective C-N coupling for urea electrosynthesis.