Unraveling the\nC–C Coupling Mechanism on Dual-Atom\nCatalysts for CO<sub>2</sub>/CO Reduction Reaction: The Critical Role\nof CO Hydrogenation

The electrochemical reduction reaction (RR) of CO to\nhigh value\nmulticarbon products is highly desirable for carbon utilization. Dual\ntransition metal atoms dispersed by N-doped graphene are able to be\nhighly efficient catalysts for this process due to the synergy of\nthe bimetallic sites for C–C coupling. In this work, we screened\nhomonuclear dual-atom catalysts dispersed by N-doped graphene to investigate\nthe potential in CO reduction to C<sub>2+</sub> products by employing\ndensity functional theory calculations. We have demonstrated that\nthe two adsorbed CO species on bimetallic sites cannot directly couple\nunless one of the CO molecules is hydrogenated. All the dual metal\natom catalysts prefer a similar coupling mechanism, i.e., the asymmetric\ncoupling of *CO on the bridged site and *CHO on the top site, while\nthe Ni<sub>2</sub> and Cu<sub>2</sub> catalysts exhibit much better\nperformance with moderate adsorption energies and low energy barriers.\nThe enhanced activities are attributed to the decrease of the energy\nlevels of *CO 2p states that weakens the metal–C bonding and\nthus facilitates the feasible C–C coupling with both low reaction\nenergies and low barriers. These insights have revealed the significant\nrole of the hydrogenation of CO species prior to the coupling step\nand may provide a theoretical perspective to understand the generation\nof C<sub>2+</sub> products in the CO<sub>2</sub>/CORR.