Enrichment of reactants and intermediates for electrocatalytic CO2 reduction.

The electrocatalytic carbon dioxide reduction reaction (CO2RR) presents a sustainable route to convert renewable electricity to value-added fuels and feedstocks in the form of chemical energy. However, the selectivity and rate of conversion of CO2 to desirable carbon-based products, especially multicarbon products, remain below the requirement for its implementation at the commercial scale, which primarily originates from inadequate reactants and intermediates near catalytic surfaces during the CO2RR. The enrichment of reactants and intermediates provides one of the coping guidelines to improve CO2RR performance by accelerating the reaction rate and improving product selectivity. Herein, we discuss strategies to achieve the enrichment of reactants and intermediates through catalyst design, local microenvironment modulation, electrolyte regulation, and electrolyzer optimization. The structure and properties of CO2 are first presented, showing the necessity and feasibility of enriching reactants and intermediates. Next, the influence of the enrichment effect on CO2 electrolysis, i.e., accelerating the reaction rate and improving product selectivity, are comprehensively discussed. Then, catalyst design from micrometer scale to atom scale, including wettability and morphology regulation, surface modification, and tandem structure construction, as well as surface atom engineering, is highlighted to implement the enrichment of reactants and intermediates. Catalyst restructuring during the CO2RR process and its impact on the enrichment of intermediates and reactants are also discussed. Subsequently, enriching CO2 reactants and intermediates by modulating the local microenvironment to achieve high carbon utilization for the CO2RR to produce multicarbon products is reviewed. After that, insights into enriching reactants and intermediates through electrolyte regulation are provided by investigating various electrolytes, including aqueous solutions, organic solvents, and ionic liquids. Additionally, the key role of electrolyzer optimization in promoting the enrichment effect is considered. We end the review by outlining the remaining technological challenges and providing feasible suggestions aimed at directing the future employment of enrichment strategies to propel the practical implementation of CO2 electrolysis technology.