Strategies to Modulate the Copper Oxidation State Toward Selective C 2+ Production in the Electrochemical CO 2 Reduction Reaction.

The electrochemical reduction of CO 2 to form value-added chemicals receives considerable attention in recent years. Copper (Cu) is recognized as the only element capable of electro-reducing CO 2 into hydrocarbons with two or more carbon atoms (C 2+ ), but the low product selectivity of the Cu-based catalyst remains a major technological challenge to overcome. Therefore, identification of the structural features of Cu-based catalysts is of great importance for the highly selective production of C 2+ products (ethylene, ethanol, n-propanol, etc.), and the oxidation state of Cu species in the catalysts is found critical to the catalyst performance. This review introduces recent efforts to fine-tune the oxidation state of Cu to increase carbon capture and produce specific C 2+ compounds, with the intention of greatly expediting the advance in the catalyst designs. It also points to the remaining challenges and fruitful research directions for the development of Cu-based catalysts that can shape the practical CO 2 reduction technology.