How to enhance the C2 products selectivity of copper-based catalysts towards electrochemical CO2 reduction?—A review

Reducing the consumption of fossil fuels and improving the utilization of carbon dioxide (CO2) are urgently needed to mitigate the effect of increasing CO2 concentration in the atmosphere, which has led to global temperature rising and climate change. Electrochemical CO2 reduction (ECR) is a promising strategy for converting CO2 into high-value-added multi-carbon compounds (such as ethylene:C2H4 and ethanol: C2H5OH) through proton coupled electron transfer (PCET) steps, in which copper (Cu) is to date the only metal that can promote C–C coupling to produce C2 products in aqueous solutions. However, due to the inherent moderate adsorption capacity of Cu on carbon-containing small molecule groups and the variety of C2 products intermediates, low product selectivity remains the dominant drawback of metal Cu-based catalysts. A large number of strategies have been investigated to optimize the distribution of electrolysis products, including alloying, anion and cation species regulation, facet design, and tandem catalysis. In this review, we first elaborate the reaction mechanism of C2 products generation on Cu-based catalysts, aiming to provide guidance for designing more selective catalysts. Then, with the intention of providing new insights into improving C2 olefins and oxides, we summarize the aspects, including catalysts, electrolytes microenvironment, electrolyzer design, and other factors that affect the selectivity of C2 products in catalytic systems. Finally, the main challenges and prospects for the future of Cu-based catalytic systems are outlined. The review is expected to stimulate more extensive studies on highly selective electrocatalysts of C2 products by ECR.