Stabilization of Cuδ+ Sites Within MnO2 for Superior Urea Electro-Synthesis.

ABSTRACT

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 Cuδ+-oxygen vacancies (Ovs)-Mn3+ dual sites is reported. Compared with pure MnO2, Cuδ+ 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 gcat. -1 in a flow cell. Remarkably, the urea yield rate remains over 78 mmol h-1 gcat. -1 across a wide potential range. Further experimental and theoretical results elucidate the unique role of Cu-MnO2 solid-solution for stabilizing Cuδ+ sites in Cuδ+-Ovs-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.