Mechanistic understanding of the electrocatalytic conversion of CO into C2+ products by double-atom catalysts

Electrocatalytic CO reduction reaction (CORR) has gained increasing attentions to generate valuable multicarbon (C2+) products, and designing high-performance electrocatalysts for CORR presents a great challenge for realizing its practical application. With the unique dual-atom site, double-atom catalyst (DAC) can provide enough geometric space to bind two CO molecules simultaneously for the key C-C coupling reaction. Herein, taking the typical 3d transition metal (TM) dimer anchored N-doped graphene (denoted as M1M2@NG) as representative, using first-principles calculations we theoretically investigate the catalytic mechanism and activity origin of CORR on DACs. It is found that the metal sites with higher d-band centers can effectively bind CO molecule, and further the d-band centers can be used as descriptors to predict the coupling free energy and coupling energy barrier for the key C-C coupling step of CO dimers. Intriguingly, among 21 candidates, CrCo and MnCo@NG DACs exhibit excellent performance for selectively generating ethanol (CH3CH2OH), with small C-C coupling energy barriers of 0.52 and 0.57 eV and ultralow limiting potentials of only -0.20 and -0.34 V, respectively, which has been further confirmed by the constant-potential simulations. Moreover, both heteronuclear CrCo and MnCo@NG exhibit significantly enhanced CORR performance compared with their homonuclear counterparts, which is ascribed to the unique d orbital synergy effect of the two different TM atoms. Our work provides rational guidelines for the design of efficient DACs for CORR, and brings useful insights into the boosted CORR performance enabled by the electronic synergy effect of the heteronuclear dual-atom site.