Why Is C-C Coupling in CO2 Reduction Still Difficult on Dual-Atom Electrocatalysts?

The emerging metal-nitrogen-carbon (M-N-C)dual-atom catalysts (DACs) have been expected to generate multicarbonproducts in the CO2 reduction reaction (CO2RR)due to the presence of multimetal sites of DACs. Unfortunately, numerousrecent experiments suggested that almost no DAC could effectivelyproduce a high quantity of multicarbon products. To uncover the reasonfor this phenomenon, we probed the surface states of typical homonuclearand heteronuclear DACs and explored the reaction mechanisms in theCO(2)RR by spin-polarized density functional theory calculationswith van der Waals interactions. Contrary to the conventional hypothesisthat C-C coupling can occur through the metal-top sites, surfacePourbaix analyses indicate that CO preferentially occupies the bridgesites between two metals, which would hinder the subsequent C-Ccoupling. Moreover, according to the energy variation, the C-Ccoupling occurring on the surface of a DAC is not feasible in boththermodynamics and kinetics. Based on the derived microkinetic modelsof DACs in the CO2RR, CO formation is more favorable thanother reduction products, which is consistent with current experimentalresults. Furthermore, we found that double-side occupancy is alsofavorable if the molecules can penetrate the carbon layer througha large defect, which would lead to a more favorable HCOOH formationin the CO2RR. By developing an analytical framework combiningsurface state analysis, activity modeling, and electronic structureanalysis, this work reveals why C-C coupling in the CO2RR remains difficult on DACs and provides insights into regulatingthe adsorption strength of *CO on the bridge site to enhance the selectivityand activity of the CO2RR at DACs.

Automated summary

Surface states of typical homonuclear and heteronuclear DACs were probed, and spin-polarized density functional theory calculations were conducted to explore the CO2RR reaction mechanisms. The study reveals the difficulty in C-C coupling on DACs and provides insights into enhancing the selectivity and activity of the CO2RR.