Spillover Promoted Dual CO2 Reduction to Ethanol via Low C-C Coupling Barrier on Co-Embedded γ-Graphyne with d-π Orbital Centers

The CO2 reduction reaction (CRR) to produce C2 products requires efficient carbon-carbon (C-C) coupling of "neighboring" 2*COs. In many previous mechanisms, the active site for C-C coupling is not necessarily a favorable active site for generating 2*CO from two CO2 . In this study, we propose a Co-embedded Boron doped graphyne (Co@B-GRY) that has a favorable CO2 reduction site, a B-doped acetylenic linker with pi-orbitals, and a Co atom with its d-orbital. Once the first CO2 is reduced to CO on the acetylenic linker, it spillovers to Co, reviving the original active site for the second CO2 reduction to CO. Then, two "neighboring" *COs can effectively couple to form C2 products. Co@B-GRY has a low C-C coupling barrier of 0.47 eV, with a low limiting potential of -0.44 V for reducing two CO2 to ethanol. Furthermore, the spillover of CO occurs with a very low barrier of 0.1 eV. This study highlights a d-pi active center that can promote C-C coupling and break the limitation of the conventional d-d type center of TM atoms that mostly relies on the diffusion of CO. Such d-pi synergy may also promote C-N coupling in urea synthesis, opening an application of sp-carbon pores.