Design of pre-catalysts for heterogeneous CO2 electrochemical reduction

CO2 reduction reaction (CO2RR) is one of the most promising methods to alleviate the global challenge of climate change and energy supply. Metal catalysts such as copper, gold, silver, tin, bismuth, etc., attract great attention for their high efficiency to convert CO2 into valuable chemicals such as CO, HCOOH, C2H4 and C2H5OH. It is of interest that the unstable metal-based compounds can be considered as pre-catalysts due to the in situ formation of a metallic state during CO2RR, resulting in a reconstruction of surface catalytic structures that mediate much higher CO2RR activity than their metal foil counterparts. However, the precise evolution process of the catalysts during CO2RR and ultimate active sites of the catalyst have not been fully tracked and determined. In this review, we summarize the recent development of metal oxides, metal dichalcogenides, metal halides, metal nitrides and metal-organic compound pre-catalysts, and focus on the structural evolution during the activation process. The key structural factors that impact the performance of catalysts are analyzed in-depth in terms of the remnant of anion elements, enhanced surface areas, facet orientation, and grain boundaries. A perspective is also provided to tackle the critical challenges in designing highly efficient CO2RR pre-catalysts, including the manipulation and identification of surface roughness, structure disorder and partial oxidation of metal center, the monitoring and regeneration of catalysts under a long-time operation, the elimination of impurities during operation and fine control of multicomponent for structural regulation.