Electrochemical CO2 reduction (CO2RR) to multi-carbon products over copper-based catalysts

•Recent Cu-based catalysts for CO2 reduction to C2+ products are summarized.•Fundamentals and calculations of CO2RR associated to chemical reaction are discussed.•Strategies including oxide, low/high-index facet, functionalized catalysts are summarized.•Challenges and outlooks in Cu-based catalysts towards CO2RR are highlighted. Copper has been recognized as the only heterogeneous catalyst leading to the formation of various products of hydrocarbons and oxygenates, such as ethanol and ethylene, from the electrochemical CO2 reduction reaction (CO2RR). Here, we first briefly summarize the fundamentals of CO2RR and discuss theoretical calculations related to the reaction process. We then critically review the recent advances to improve the activity and selectivity of CO2 reduction to multi-carbon (C2+) products over Cu-based nanomaterials. First, oxide and halide-derived Cu NPs are reviewed for CO2RR based on different factors including sub-surface oxides, Cu+ species, and grain boundaries. Then, the low- and high-index facet Cu nanocrystals are discussed for CO2RR in detail. Under this section, we raise the question: “single or multi-facet enclosed nanocrystals for a greater CO2 reduction selectivity to C2+ products?” We also review other Cu-based nanostructures including surface-functionalized and confined Cu catalysts for CO2RR. Generally, this review aims to provide new insights and offer better comprehension of the advances and progress of the research domain. In conclusion, some outlooks are delivered on the upcoming research path of the CO2RR selectivity toward C2+ products over Cu-based catalysts.