Exciton Dynamics and Photocatalytic Degradation Mechanism of Graphitic Carbon Nitride Nanostructures in Water Splitting

Project: Research

View graph of relations

Description

Using solar energy to split water into H2 and O2 is a desirable and “clean” approach toresolving the energy crisis. It is particularly viable when a photoelectrochemical (PEC)water splitting technique is used. The technique would be effective if the photoelectrodematerial could efficiently absorb visible sunlight, transport charge carriers, and remainstable. A promising new candidate for such a material is graphitic carbon nitride (g-CN),according to our recent demonstration. While it is still necessary to achieve large-areathin film deposition, improved charge carrier mobility and full-spectrum absorption, thismaterial also requires further development in order to reduce photocatalytic degradationin water splitting.To obtain strategies for reducing photocatalytic degradation, we propose in this projectto systematically investigate the exciton dynamics and possible photoinduced chemicalreactions of various g-CN nanostructures in water splitting under visible light. Towardsthe goal, we will use time-dependent density functional theory and its tight-bindingapproximation to perform the excited-state molecular dynamics simulations for theneutral and charged g-CN nanostructures. The simulation will be conducted at variouspossible temperatures (ranging from 230K to 320K) likely to be experienced inapplications. We will do so in water containing OH- or H+ and sacrificial reagent (e.g.Na2S and triethanolamine) as well as in the presence of the O atoms and moleculesgenerated from water splitting. The charged g-CN models will be used to simulate theelectron rich and deficient cases due to n- and p-type dopings. We will examine theexciton generation, localization, and migration, and the related chemical reactions, inorder to understand the photocatalytic degradation of g-CN. We will identify the atomand bond changes arising from the excitations and characterize the time evolution of theexcited electron and hole distributions in the g-CN. In doing so we will pay particularattention to the possibility of inducing structural instability and deformation and theeffects of the various possible species in the water environment. The excited-statechemical reactions we identify will then be quantitatively studied using transition statetheory and the nudged elastic band method to derive their kinetic characteristics. Weexpect our simulations to reveal the degradation mechanism of g-CN due to the excitongeneration in the g-CN and oxygen atoms and molecules generated on the electrodesurface. This will allow us to propose strategies to minimize the degradation so as tocontribute to the important development of PEC water splitting using g-CN.

Detail(s)

Project number9042399
Grant typeGRF
StatusFinished
Effective start/end date1/01/1729/11/21

    Research areas

  • Graphitic carbon nitride , Exciton dynamics , Excited state simulation , Water splitting , Photocatalytic degradation