Transition-metal-embedded boron-doped graphene for reduction of CO2 to HCOOH†

Abstract

The electrochemical conversion of carbon dioxide is an excellent strategy for alleviating the greenhouse effect. Lately, single-atom catalysts have gained notable attention as emerging candidates for the CO₂ reduction reaction owing to their remarkable cost-efficiency and unprecedented atomic utilization. By applying the density functional theory (DFT), our work examines the first couple of proton-coupled electron transfer steps of the CO₂RR on 3d transition metal-doped B-Gr and compares the activity observed with previously studied supports. Since CO₂ activation is the first step of the CO₂RR, we thoroughly investigated the capability of the TM SAs in effectively activating CO₂, both in the dry phase and in the presence of water. According to our calculation, except for Ti, Cu and Zn, all other TM@B-Gr systems can activate the CO₂ molecule. CO₂ activation on the selected SACs is further attributed to the transfer of charges from the TM SA to the CO₂ molecule, as revealed by our Bader charge calculations. In addition, the Gibbs free energy changes for all the reaction intermediates are calculated to determine the most preferred pathway of the reaction. Our results indicate a preference for OCHO over COOH in the first protonation step, indicating the production of HCOOH as the preferred end product. The same trend is also observed in the presence of H₂O. Our DFT-based analysis presented in this work reveals the crucial role that a support plays in determining the activity of a single-atom catalyst and paves the way for the efficient design of 2D catalysts for the CO₂ reduction reaction.