Advanced progress in constructing carbon-coated metal materials for electrocatalytic CO2 reduction

Due to mild reaction conditions and usage of clean electricity, electrocatalytic CO2 reduction reaction (CO2RR) is considered as ideal way to achieve the goal of CO2 emission reduction and carbon cycling. Notably, the development of efficient metal-based electrocatalysts with low cost and high activity is the key for wide application of CO2RR electrolysis. Among these materials, recently carbon-coated metal-based catalysts have drawn more attention, because outer carbon not only avoids the deterioration of metal active sites caused by electrolyte corrosion, but also protects metal active sites from electrochemical oxidation and physical agglomeration. However, too thick carbon layer will prevent exposure of active metal sites, while too thin carbon layer can't protect metal sites from corrosion or oxidation of the electrolyte. Therefore, developing excellent carbon-coated metal catalyst with a suitable carbon-shell thickness is a major challenge. In this work, the advanced progress of carbon-coated materials for CO2RR is reviewed. According to carbon-coated metals, they are classified as carbon-coated monometal and carbon-coated bimetal catalysts. Noticeably, bimetallic tandem catalysts provide a promising strategy for locally increasing the intermediate CO, thereby maximizing C-C coupled products. Moreover, the superior performance for CO2RR is further improved by nitrogen-doping in carbon. Benefitting from this carbon-coated metal structure, efficient materials can be obtained. For example, the resulting NiMOF@NC exhibits high CO Faradaic efficiency (FE) of 99 % and current density of -26.3 mA cm(-2) at 1.0 V (vs RHE). FECO can be maintained above 90 % during the wide potential range of -0.8 similar to -1.4 V(vs RHE). For CuOx@C, it shows high FEethanol of 46 %. While for Cu@ZIF-8 NWs with core@shell structure, it displays excellent stability and a high Faraday efficiency of 57.5 % for hydrocarbons (CH4 and C2H4) at a potential of 0.7 V (vs RHE). Finally, some challenges and prospects encountered in the current study of CO2RR are proposed. This review supports an important guidance for constructing efficient carbon-coated metal materials for electrocatalytic CO2 reduction.