Mechanistic study on the competition between carbon dioxide reduction and hydrogen evolution reaction and selectivity tuning via single-atom catalyst loading on graphitic carbon nitride

Abstract

In the context of catalytic CO2 reduction, the interference from the inherent hydrogen evolution reaction (HER) and the possible selectivity towards CO has posed a significant challenge in the CO2 reduction reaction to formic acid (HCOOH). To address this hurdle, we have investigated the impact of different single atom metal catalysts on tuning the selectivity by employing density functional theory (DFT) to scrutinize the reaction pathway. Single-atom catalyst (SACs) supported on carbon-based systems have proven to be pivotal in altering both the activity and selectivity of the CO2 reduction reaction. In this study, a series of single-atom-metal loaded g-C3N4 monolayers (MCN, M = Ni, Cu, Zn, Ga, Cd, In, Sn, Pb, Ag, Au, Bi, Pd and Pt) were systematically examined. Through detailed DFT calculations, we explored their influence on the reaction selectivity between *COOH and *OCHO intermediates. Notably, NiCN favors the reaction via the *OCHO route with a significantly lower rate-determining potential at 0.36 eV, which is approximately 73.5% lower in comparison to the CN system (1.36 eV). Most importantly, the Ni SACs with smaller atomic radii (0.124 nm) was shifted to the corner position of the carbon nitride forming lower coordination that significantly enhances the CO2 adsorption, promoting the CO2 reduction over HER. Overall, this study provides a theoretical prediction of how the selection of single-atom metal catalysts (SACs), guided by DFT studies, effectively modulates the reaction pathway, thereby offering the potential solution for the high selectivity in CO2 reduction products.