Stabilization of Cu^δ+ Sites Within MnO₂ for Superior Urea Electro-Synthesis

Electrocatalytic C-N coupling between NO₃ ^- and CO₂ has emerged as a sustainable route for urea production. However, identifying catalytic active sites and designing efficient electrocatalysts remain significant challenges. Herein, the synthesis of Cu-doped MnO₂ nanotube (denoted as Cu-MnO₂) with stable Cu^δ+-oxygen vacancies (O_vs)-Mn³⁺ dual sites is reported. Compared with pure MnO₂, Cu^δ+ doping can effectively enhance urea production performance in the co-reduction of CO₂ and NO₃ ^-. Thus, Cu-MnO₂ catalyst exhibits a maximum Faradaic efficiency (FE) of 54.7% and the highest yield rate of 116.7 mmol h^-1 g_cat. ^-1 in a flow cell. Remarkably, the urea yield rate remains over 78 mmol h^-1 g_cat. ^-1 across a wide potential range. Further experimental and theoretical results elucidate the unique role of Cu-MnO₂ solid-solution for stabilizing Cu^δ+ sites in Cu^δ+-O_vs-Mn³⁺, endowing the catalyst with superior structural and electrochemical stabilities. This thermodynamically promotes urea formation and kinetically lowers the energy barrier of C-N coupling.