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Among various studied catalysts, copper-based electrocatalysts can convert CO2 into hydrocarbons. Two main challenges in this research area are low selectivity, especially for value-added C2+ products and the high overpotentials required to initiate carbon dioxide reduction reaction (CO2RR). The interaction between copper and oxygen has always been inevitable in the design of copper-based catalysts owing to the intrinsic activity of copper and the oxygen-rich environment we live in. Recently, due to the unprecedented development of in-situ characterization, continuously increasing attention has been paid to oxygen species, which is usually accounting for the highest proportion of metalloid composition in copper-based catalysts. Herein, we have summarized the research progress on oxygen-containing copper catalysts, both experimentally and theoretically, and revealed the evolution of oxygen and the relationship between catalytic performance and oxygen species. It is found that the existence of subsurface oxygen in the electrochemical interface of copper-based electrodes has been proved both by in-situ characterization and theoretical simulation, which is also essential for efficient CO2RR to C2+ products. Additionally, selectivity to C2+ products is basically boosted in three ways: facilitating the conversion of CO2 from physical adsorption to chemical adsorption, strengthening intermediate binding and optimizing the adsorption configuration of CO2. It is expected that this review will provide clue for utilizing oxygen to enhance C2+ selectivity in the design of copper-based catalysts.

Developing a facile strategy for universal synthesis of transition metal catalysts is significant to catalytic reactions but remains challenging. Herein, we report an ultrafast one-step electrodeposition method to prepare a series of transition metal foams within one minute for electrocatalytic water splitting. The porous metal foams not only possess unique 3D channels for rapid electrolyte diffusion and gas releasing, but also have robust integrated structures with enhanced conductivity for efficient charge transport. Consequently, the NiCo and NiFe foams only require 86 and 206 mV to output 10 mA cm−2 for hydrogen and oxygen evolution reactions (HER and OER) in 1 M KOH, respectively. Combining the two electrocatalysts, we have assembled an outstanding alkaline electrolyzer, requiring only 1.52 and 1.64 V to deliver 10 and 100 mA cm−2 respectively, outperforming the RuO2(+)//Pt/C(-) electrolyzer. Our study offers an ultrafast and general approach to fabricate 3D porous electrocatalysts for high-performance water splitting.