Exploration of the bio-analogous asymmetric C–C coupling mechanism in tandem CO2 electroreduction

C–C coupling is a critical step of CO2 fixation in constructing the carbon skeleton of value-added multicarbon products. The Wood–Ljungdahl pathway is an efficient natural process through which microbes transform CO2 into methyl and carbonyl groups and subsequently couple them together. This asymmetric coupling mechanism remains largely unexplored in inorganic CO2 electroreduction. Here we experimentally validate the asymmetric coupling pathway through isotope-labelled co-reduction experiments on a Cu surface where 13CH3I and 12CO are co-fed externally as the methyl and the carbonyl source, respectively. Isotope-labelled multicarbon oxygenates were detected, which confirms an electrocatalytic asymmetric coupling on the Cu surface. We further employed tandem Cu–Ag nanoparticle systems in which *CHx and *CO intermediates can be generated to achieve asymmetric C–C coupling for a practical CO2 electroreduction. We found that the production of multicarbon oxygenates is correlated with the generation rate of two intermediate indicators, CH4 and CO. By aligning their rates, the oxygenates generation rate can be maximized. An asymmetric C–C coupling (Wood–Ljungdahl) pathway has long been known in biological carbon fixation, whereas its occurrence in inorganic systems has remained unclear. In this study, the coupling of *CO and *CHx intermediates to form multicarbon oxygenates has been experimentally observed on Cu electrodes.