Electrochemical reduction of carbon dioxide on the oxide-containing electrocatalysts

Electrochemical reduction of carbon dioxide (CO 2 RR) is one of the promising approaches to mitigate the climate-change effects through a negative CO 2 emission technology while producing value-added products. Significant advances in CO 2 RR have been achieved on various metal electrocatalysts to produce a variety of products in gas, liquid, or even solid forms. The frequently used metals such as Ag, Au, Bi, Cu, Sn, and Zn may contain oxide species that were either intentionally or unintentionally formed during the syntheses. For the oxide-derived catalysts, the oxides are pre-catalyst active forms, which are reduced under the CO 2 RR environment and thus affected the physical/chemical properties of the final catalysts. On the other hand, oxide species (MO x , M + , or O 2 /O - ) can directly enhance CO 2 activation, C−C coupling, dimerization, and/or modify the surface electronic states of the active species for CO 2 RR. In this review, we provide the latest progress towards understanding the roles of oxide-containing electrocatalysts in CO 2 RR. The nature of oxides on various groups of metal electrocatalysts as categorized by their major products [e.g., CO, CH 4 , HCOOH, CH 3 OH, C 2 H 5 OH, C 2 H 4 , and C (solid)] and their roles in the direct and in-direct effects for improving the CO 2 RR performances has been emphasized. • Different forms of oxides in electrochemical reduction of carbon dioxide. • Direct and indirect roles of oxide in CO 2 RR electrocatalysts. • Metal oxide encourages C-C coupling and increases CO 2 adsorption capacities. • Metal species facilitates CO 2 activation and dimerization of intermediate *CO. • Oxygen involves in the change of electronic state.