First principles investigation of cobalt-phthalocyanine active site tuning via atomic linker immobilization for CO₂ electroreduction

We investigate the CO₂ electroreduction reaction (CO₂ERR) using first principles calculations, for the active site tuning of cobalt phthalocyanine (CoPc) via distinct atomic linker species which immobilize CoPc on a carbon nanotube (CNT) substrate. Eight different linker species are studied, along with the effect of linker hydrogenation. Superior reaction performance is predicted for the NH, S and PH linkers, which show activated CO₂ adsorption. This results from spin polarization causing unoccupied d_z² spin-down states of the cobalt active site at, or above, the Fermi level. Using an ‘on-catalyst’ reaction scheme, calculated activation barriers for COOH formation and CO desorption are lower for the CoPc-PH-CNT system compared to the CoPc-NH-CNT system and CoPc remains attached to PH-CNT throughout the reaction. We thus expect the PH linker system to have similar or better CO₂ERR performance compared to the NH and S linker systems but at a slightly higher electrode potential.