Theoretical study on the performance of g-C3N4 loaded silver nanoparticles (Ag4, Ag8, Ag13) catalysts and their electrocatalytic reduction mechanism of CO2

Abstract

In this study, density functional theory (DFT) was employed to model Ag₄, Ag₈, and Ag₁₃ nanoparticle-supported g-C₃N₄ catalysts. The stability of the Ag₄, Ag₈, and Ag₁₃ nanoparticle-supported g-C₃N₄ catalysts was rigorously confirmed, followed by the computation of electron density and differential charge density profiles. The adsorption configuration of CO₂ on the catalyst surfaces was optimized, revealing that the adsorption process is predominantly governed by chemisorption. It was determined that the activation of this process is intricately linked to the electronic interactions between CO₂ molecules and the catalyst surface. Furthermore, the study explored the mechanisms underlying the electrochemical reduction of CO₂, with a focus on elucidating the production pathways of four key products: HCOOH, CO, CH₃OH, and CH₄, across the three catalysts. The free energy profiles along the reaction pathways were analyzed to compare the selectivity and catalytic activity of the three catalysts for various reduction products. Among the catalysts studied, the Ag₄-supported g-C₃N₄ catalyst exhibited the highest selectivity for the electrochemical reduction of CO₂ to HCOOH. Additionally, the study demonstrated that an increase in the size of the Ag nanoparticles correlates with an enhanced selectivity for CO as a two-electron reduction product, while the catalytic activity for multi-electron reduction products such as HCOOH, CH₃OH, and CH₄ decreases. Band structure and density of states calculations for the three Ag nanoparticle-supported catalysts revealed an inverse correlation between band gap values and catalytic activity, with smaller band gaps associated with higher catalytic activity. This work provides critical insights into the relationship between Ag nanoparticle size and CO₂ electrocatalytic reduction activity, offering a theoretical foundation for the design of advanced CO₂ reduction catalysts.