Towards superior CO2RR catalysts: Deciphering the selectivity puzzle over dual-atom catalyst

The electrocatalytic CO2 reduction reaction (CO2RR) is one of the most important electrocatalytic reactions. Starting from a well-defined *CO intermediate, the CO2RR can bifurcate into two pathways, either forming a hydrogenation product by * C O bond hydrogenation or leading to CO desorption by * C bond cleavage. However, it is perplexing why many dual-atom catalysts (DACs) exhibit high CO selectivity in experiments, despite previous theoretical studies arguing that the * C O bond hydrogenation is thermodynamically more favorable than the * C bond breaking. Furthermore, the selectivity is contingent upon the potential and is perturbed by the hydrogen evolution reaction (HER), which is far from clear. Using ab initio molecular dynamics and a "slow-growth" sampling method to evaluate the potential-dependent kinetics, we uncover the selectivity origin of CO2RR to CO on a typical NC-based DAC (CuFe-N6-C). Importantly, the results show that at higher CO* coverage, CO* desorption kinetics are accelerated, while the competing * C O bond hydrogenation reaction is inhibited at varying potentials. Furthermore, the selectivity of the HER is observed to increase as the potential decreases. However, at higher CO* coverage, the energy barrier for the * C bond cleavage is lower than that for HER, suggesting that HER is suppressed on CuFe-N6-C. Our work unlocks a long-standing puzzle about the selectivity of important DAC catalysts for CO2RR and provides insights for more effective catalyst design.