Theoretical investigations of Metal-N4-Graphene and Metal-C3N4 catalysts for CO2 reduction
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In the present work, we performed density functional theory (DFT) calculations to investigate the nature of the active sites, their structures, and the associated free energies to achieve CO or HCOOH formation during CO2 reduction (CO2RR) in preference to generating H2 in HER on Me-N4-doped Graphene/ Carbon Nanotube and Me-C3N4 catalysts. We find that for Me-N4-doped Graphene / Carbon Nanotube systems, there exists a scaling relation between the adsorption energies of *H and *COOH, the intermediates of hydrogen evolution reaction (HER) and CO2 reduction reaction to CO. However, only the ‘butterfly’ form of graphene and carbon nanotube as support for the Me-N4 active site lead to CO pathway with the formic acid pathway being more favorable in CO2RR than HER. As for Me-C3N4 catalysts, the adsorption energies on di-metal-C3N4 catalysts are larger than for mono-metal-C3N4 catalysts, and only NiMn-C3N4 catalysts leads to CO pathway being the dominant reaction pathway over HER.