Oriented external electric field effect for C-C coupling reaction on graphyne surface

In the electrocatalytic CO₂ reduction reaction, the production of high value multi-carbon products has been hindered by the high barrier to carbon-carbon (C-C) coupling. Oriented external electric fields (OEEFs) have been shown to promote reactions. We evaluated the active control of the C-C coupling reaction by OEEF on the graphyne (GRY) surface, an interesting carbon allotrope characterized by sp-sp² hybridized carbon bonds. The reaction energy and activation energy were calculated for the key C-C coupling reaction, 2*CO → *OC-CO, using both cluster cutouts and periodic models. We found that aligning the electric field perpendicular to the surface reduced the C-C coupling barrier. Interestingly, the OEEF in the direction of the newly formed C-C bond had a smaller effect on reactivity. Electron density modifications by the perpendicular electric field showed that electron density to the C-C coupling region is promoted for GRY, but not for the boron doped graphyne with the electron deficient boron in the linker. Furthermore, the electric field along the newly formed C-C bond modulated electron density only on the GRY surface, not on the reactive adsorbates, so the OEEF effect was minor in this direction.