Unveiling the kinetic mechanism of oxygen vacancy and N-doping co-modified SrTiO3(100) for photocatalytic conversion of CO2 and H2O into CH4via associative proton transfer: insights from ab initio molecular dynamics

Abstract

Photocatalytic conversion of CO₂ and H₂O into valuable CH₄ has emerged as an appealing strategy for environmental remediation and sustainable energy production. However, a fundamental understanding of the kinetic mechanisms governing the full elementary reaction chain at the atomic scale in H₂O-mediated CO₂ reduction has remained elusive. Therefore, this study combines density functional theory (DFT) and ab initio molecular dynamics simulations with the slow-growth sampling (SG-AIMD) method to explore the kinetic characteristics of the full elementary reaction chains in the photocatalytic conversion of CO₂/H₂O to CH₄. The calculation results reveal the kinetic preference for CO₂ adsorption at the TiO-terminated SrTiO₃(100) gas–solid interface and further elucidate the dominant role of the associative proton transfer mechanism in both CO₂ protonation and the hydrogen evolution reaction (HER). More importantly, the nitrogen (N)-doped surface with oxygen vacancies (Vo) introduces shallow defect states below the conduction band minimum (CBM), enhancing electron injection upon photoexcitation. Furthermore, it promotes the activation of the *COOH intermediate, which significantly lowers the reaction kinetic barrier. This dual functionality collectively accelerates the H₂O-mediated proton transfer kinetics in the photocatalytic conversion from CO₂/H₂O to CH₄. This work unveils the dynamic evolution mechanism of photocatalytic CO₂/H₂O → CH₄ at the atomic scale, offering theoretical guidance for the design of efficient solar fuel catalysts.