A Computational Study on the Mechanisms of Nonmetal Doping and Doping-induced Stability Enhancement of Graphitic Carbon Nitride Nanostructures for Photoelectrochemical Water Splitting
DescriptionGraphitic carbon nitride (g-CN) materials are promising photocatalysts for photoelectrochemical (PEC) applications such as splitting water into H2 and O2, which are ideal clean chemical energy carriers that produce only water after combustion. Although recently we successfully achieved depositions of the uniform, large-area, and pinhole-free g-CN thin films that are required for PEC applications, the films’ charge carrier conductivity and stability are still low for PEC applications. Although doping is a straightforward approach for improving conductivity, the complicated results obtained to date often cannot be understood with conventional doping mechanisms. Interestingly, we have recently observed that certain doping not only can improve the conductivity of charge carriers but also can significantly improve the chemical stability of the g-CN films. Systematic computational studies are needed for understanding the underlying mechanisms, in order to guide optimization of the doping and PEC conditions for urgent green energy applications.We believe that surface passivation and charge transfer doping mechanisms play important roles in the doping of g-CN. Thus, in this project we propose to perform computational simulations for an optimal doping design, in order to complement previous researches that were based on substitutional and interstitial doping mechanisms. We will model the doping systems by placing nonmetal dopants such as B, C, N, O, S, P, and halogen atoms, as well as their compounds used in experimental doping, in g-CN nanostructures. We will simulate the accumulation of these atoms and species in the surface regions, as well as the adsorption of water molecules and other possible species, such as H+/OH- and sacrificial agents (e.g., Na2S and triethanolamine), that are used in PEC water splitting. Our calculations will include ground- and excited-state calculations for structural optimizations and molecular dynamics simulations of the model systems, transition state searches of the possible chemical reactions involved, and charge transfers as well as band structure calculations, using the most sophisticated density functional theory methods available and their time-dependent approaches. We expect our computational studies to deliver the needed knowledge about doping types and configurations determined by charge transfers, which provide the carriers for conduction due to the dopant accumulation at the interface and surface as well as the adsorptions onto the g-CN surface with species from the electrolyte. We will also reveal the interfacial chemical reactions involving dopants in PEC applications and will identify the reactions with products that stabilize the intended surface from photoinduced degradation of the g-CN material.
|Effective start/end date||1/01/19 → 9/12/22|