Controlling C-C coupling reactivity through pore shape engineering of B-doped graphyne family

Graphyne is an interesting carbon allotrope characterized by sp-sp2 hybridized carbon bonds, which allow for structure variability. Though there are studies evaluating the electrical and mechanical properties of various structures, studies utilizing its structural variety toward catalyst applications are minor. In electrocatalytic CO2 reduction reactions (CRR), producing valuable C2+ products, such as C2H4 or C2H5OH, under mild conditions is still challenging. The bottleneck has been assigned to the carbon-carbon (C-C) coupling reaction, such as 2*CO -> *OCCO. In this reaction, one requires strong binding to the catalyst to enhance neighboring CO concentration, but at the same time, one needs to have low C-C coupling barriers making the OC-CO bond. Following our previous study, which showed B-doped gamma-graphyne can be a catalyst for ethanol production, we conducted theoretical investigations on a range of B-doped graphyne families using density functional theory. Out of the 15 different structures studied, four, 4,12,2-, sR-, gamma-, and 6,6,12-graphynes, show promising potential for CRR. B -doped 4,12,2-graphyne, with small square and rectangular pores, had a very low C-C coupling barrier of 0.34 eV with strong 2*CO adsorption (-2.5 eV). Furthermore, our research revealed a correlation between the heat of reaction (2*CO -> *OCCO) and the average pore area around the acetylenic linker reaction site. Smaller pores give a favorable orientation of two CO molecules, resulting in low reaction barriers.