Prediction of Potential-Dependent Kinetics for the\nElectrocatalytic Reduction of CO<sub>2</sub> to CO over Ti@4N-Gr

Grand\ncanonical density functional theory (GC-DFT) was employed\nto model the electrocatalytic reduction of CO<sub>2</sub> (CO<sub>2</sub>R) to CO by single titanium atom nitrogen-doped graphene,\nreferred to as Ti@4N-Gr. Previous GC-DFT thermodynamic investigations\nhave identified Ti@4N-Gr as a promising CO<sub>2</sub>R catalyst;\nhowever, no in-depth studies have examined it. In this study, we analyze\nactivation energies of the elementary steps at various applied potentials\nin addition to thermodynamics of CO<sub>2</sub>R to CO catalyzed by\nTi@<i>x</i>N-Gr defects. Reaction intermediates are predicted\nto be destabilized when Ti is coordinated to fewer N atoms. Based\non reaction thermodynamics, Ti@4N-Gr and all defect configurations\nare predicted to be potentially promising catalysts for CO<sub>2</sub>R to CO at an applied potential of −0.7 V<sub>SHE</sub> while\nat −0.3 and −1.2 V<sub>SHE</sub> the reaction is predicted\nto be hindered by relatively large grand free energy differences between\nintermediates. We propose a criterion to identify optimum applied\npotentials for CO<sub>2</sub>R to CO based on the potential of zero\ncharge (PZC) of the reaction intermediates and the contention that\nthe optimum applied potential for CO<sub>2</sub>R to CO lies in the\nrange PZC*CO2O molecules form strong hydrogen bonds\nwith the *COOH intermediate, especially at more oxidizing potentials,\nwhich increases the energetic costs required for the protonation of\n*COOH by 0.18 to 0.43 eV at applied potentials of −1.2 to −0.3\nV<sub>SHE</sub>. Grand canonical nudged elastic band (GC-NEB) was\nused to predict the activation barriers of CO<sub>2</sub>R to CO catalyzed\nby Ti@4N-Gr. GC-NEB predicts that all activation barriers along the\nreaction pathway are potential-dependent, where CO desorption and\nCO<sub>2</sub> adsorption have the largest barriers at highly reducing\nand highly oxidizing potentials, respectively.