Modeling the Potential-Dependent Kinetics of CO2 Electroreduction on Single-Nickel Atom Catalysts with Explicit Solvation

Single-metal atom catalysts in nitrogen-doped graphene supports have attracted growing attention as state-of-the-art CO2 reduction reaction (CO2RR) electrocatalysts. Nevertheless, theoretical explorations on such systems remain immensely insufficient owing to the complexity in realistic modeling of the solid/liquid interface and the lack of understanding of the potential dependence of the reaction mechanisms and the catalytic nature of active sites. In this work, we develop a methodology of Langmuir adsorption model-derived potential-dependent kinetics (LPD-K) to probe the potential-dependent kinetics of the CO2RR on single-atom electrocatalysts. Using this LPD-K method, we show how to predict the potential-dependent chemistry using a specific example, single-nickel atom nitrogen–graphene catalysts (NiNnC4–n@Gra, n = 1–4). We investigate the reaction mechanisms and energetics at the electrochemical interface using ab initio molecular dynamics (AIMD) simulations with fully explicit solvation, in conjunction with thermodynamic integration methods and electrode potential analysis. The effect of the applied electrode potential on the free energetics of the CO2RR on NiNnC4–n@Gra is comprehensively discussed. It is suggested that both reaction energies and barriers for CO2 adsorption and further protonation are approximately linearly correlated with the applied electrode potentials but the slopes are distinctly deviated from 1 eV per volt. Based on the correlations of potential-dependent free energetics and the proposed kinetic model, we predict the onset potentials of the CO2RR under both basic and acidic conditions, which are comparable with the experimental observations. In addition, our findings reveal the structural impact of the catalytic activity of a single-Ni atom catalyst with different coordination environments. In a broad sense, probing the structural origin and thermodynamic CO2RR analysis could inspire the rational design of efficient MNC@Gra-based CO2RR catalysts.