Boosting CO2 electroreduction to formate via bismuth oxide clusters

Supported metal (oxide) clusters, with both rich surface sites and high atom utilization efficiency, have shown improved activity and selectivity for many catalytic reactions over nanoparticle and single atom catalysts. Yet, the role of cluster catalysts has been rarely reported in CO2 electroreduction reaction (CO2RR), which is a promising route for converting CO2 to liquid fuels like formic acid with renewable electricity. Here we develop a bismuth oxide (BiOn) cluster catalyst for highly efficient CO2RR to formate. The BiOn cluster catalyst exhibits excellent activity, selectivity, and stability towards formate production, with a formate Faradaic efficiency of over 90% at a current density up to 500 mA·cm−2 in an alkaline membrane electrode assembly electrolyzer, corresponding to a mass activity as high as 3,750 A·gBi−1. The electrolyzer with the BiOn cluster catalyst delivers a remarkable formate production rate of 0.56 mmol·min−1 at a high single-pass CO2 conversion of 44%. Density functional theory calculations indicate that Bi4O3 cluster is more favorable for stabilizing the HCOO* intermediate than Bi(001) surface and single site BiC4 motif, rationalizing the improved formate production over the BiOn cluster catalyst. This work highlights the great importance of cluster catalysts in activity and selectivity control in electrocatalytic CO2 conversion.