Stabilization of Cu δ+ Sites Within MnO 2 for Superior Urea Electro-Synthesis.

Electrocatalytic C-N coupling between NO 3 - and CO 2 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 MnO 2 nanotube (denoted as Cu-MnO 2 ) with stable Cu δ+ -oxygen vacancies (O vs )-Mn 3+ dual sites is reported. Compared with pure MnO 2 , Cu δ+ doping can effectively enhance urea production performance in the co-reduction of CO 2 and NO 3 - . Thus, Cu-MnO 2 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-MnO 2 solid-solution for stabilizing Cu δ+ sites in Cu δ+ -O vs -Mn 3+ , endowing the catalyst with superior structural and electrochemical stabilities. This thermodynamically promotes urea formation and kinetically lowers the energy barrier of C-N coupling.