Prediction of Potential-Dependent Kinetics for the Electrocatalytic Reduction of CO₂ to CO over Ti@4N-Gr

Grand canonical density functional theory (GC-DFT) was employed to model the electrocatalytic reduction of CO2 (CO2R) to CO by single titanium atom nitrogen-doped graphene, referred to as Ti@4N-Gr. Previous GC-DFT thermodynamic investigations have identified Ti@4N-Gr as a promising CO2R catalyst; however, no in-depth studies have examined it. In this study, we analyze activation energies of the elementary steps at various applied potentials in addition to thermodynamics of CO2R to CO catalyzed by Ti@xN-Gr defects. Reaction intermediates are predicted to be destabilized when Ti is coordinated to fewer N atoms. Based on reaction thermodynamics, Ti@4N-Gr and all defect configurations are predicted to be potentially promising catalysts for CO2R to CO at an applied potential of −0.7 VSHE while at −0.3 and −1.2 VSHE the reaction is predicted to be hindered by relatively large grand free energy differences between intermediates. We propose a criterion to identify optimum applied potentials for CO2R to CO based on the potential of zero charge (PZC) of the reaction intermediates and the contention that the optimum applied potential for CO2R to CO lies in the range PZC*CO<V<PZC*CO2− that can be generalized to other electrocatalytic systems. Solvating H2O molecules form strong hydrogen bonds with the *COOH intermediate, especially at more oxidizing potentials, which increases the energetic costs required for the protonation of *COOH by 0.18 to 0.43 eV at applied potentials of −1.2 to −0.3 VSHE. Grand canonical nudged elastic band (GC-NEB) was used to predict the activation barriers of CO2R to CO catalyzed by Ti@4N-Gr. GC-NEB predicts that all activation barriers along the reaction pathway are potential-dependent, where CO desorption and CO2 adsorption have the largest barriers at highly reducing and highly oxidizing potentials, respectively.