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 *CO 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 *CO 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 *CO 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.