Critical Role of Reaction Kinetics in Selectivity Control of Electrochemical CO ₂ Reduction on Copper-Based Single-Atom Alloys

Copper is a promising catalyst for the electroreduction of CO2 (eCO2RR). Recently, copper-based single-atom alloys (Cu-SAAs) have been widely used to tune the selectivity of the eCO2RR. In experiments, the dominant product can be distinct when different single metal atoms are embedded in Cu, while the fundamental reasons are not clear. In this work, we demonstrated that the thermodynamic investigation of the key intermediates, COOH* and HCOO*, is not sufficient to rationalize the selectivity of Cu-SAAs. We found that the kinetics plays a critical role in selectivity control. The electrochemical barrier calculations and microkinetic simulations indicate that HCOOH is the dominant product on CuPb1 via the COOH* intermediate, beyond the conventional understanding that HCOOH is produced via HCOO*. However, on CuSb1, CO shows higher selectivity than HCOOH due to the lower barrier for associative hydrogenation and dissociation of COOH* to CO* than for HCOOH* production. These simulated results agree well with previous experiments, providing valuable kinetic insights into the selectivity of the eCO2RR on Cu-SAAs.