Navigating CO utilization in tandem electrocatalysis of CO2

The transformation of CO2-to-C2+ products on Cu catalysts suffers from limited C2+ selectivity and productivity due largely to sluggish C–C coupling kinetics. Sequential cascade CO2-to-C2+ product conversion, integrating the first step CO2-to-CO and second step CO-to-C2+ conversion in series on two distinct but complementary catalysts has been widely accepted as an effective approach to improve the *CO coverage that facilitates the C–C coupling rate. This review addresses the mechanism and design principles of tandem systems for CO2 reduction, with a focus on tandem reduction in one electrolyzer. First, we analyze the crucial role of the adsorbed *CO in the C–C coupling process. Second, we thoroughly discuss the core design principle of the CO2 tandem reduction systems: enhancing the CO utilization efficiency, navigated by improving CO intermediate transport, balancing the CO generation and utilization rate, and matching the CO generation and utilization overpotential between two independent catalysts. Third, we introduce the widely used technique to prepare the tandem catalysts and electrodes. Finally, we offer some perspectives on the outlook for CO2 tandem reduction.