Theoretical Study On Hydrogen Production By Doping Graphitic Carbon Nitride（G-C₃N₄） As Photocatalyst And Electrocatalyst

The chemical doping of graphite phase carbonized nitrogen(g-C3N4)is one of the important means to enhance its catalytic activity.In this paper,the density functional theory(DFT)is used to systematically study the doping of non-metallic elements and metal elements to the two-dimensional semiconductor material g-C3N4,such as influence of electronic structure and photocatalytic and electrocatalytic activity.The main conclusions are summarized as follow:1.The electronic structure,light absorption and carrier transport properties of non-metallic element doping on g-C3N4 are systematically studied.The design principle of a general non-metallic element doped g-C3N4 is first explained.It is also used for conventional metal oxide semiconductors such as TiO2,ZnO.Conclusions show that the mobility of carriers is the dominant factor affecting the photocatalytic activity of doped structures.These predictions are consistent with experimental measurements.This design principle can also be extended to other photoreduction reactions such as carbon dioxide reduction.2.The study on the physical properties of the metal cation doped structure shows that the light absorption capacity,carrier transport characteristics and metal element binding ability of the metal doping model determine its photocatalytic hydrogen production activity,and can accurately predict the hydrogen production rate of the doping models.We also propose a descriptor that is only related to the metal element and the basic structure.3.A new descriptor is developed to characterize the p-block element doping g-C3N4 as a catalyst design principle for electrocatalytic hydrogen production.It is related to the electron attraction and bonding environment of heteroatoms.Furtherly,we reveal the essential factor for the adsorption strength between hydrogen atoms and active sites.The highest position of the state density of the adsorbed hydrogen atom at the bottom of the conduction band determines the strength of the chemical bond between the active site and hydrogen atom.For the first time,we discovered the descriptors of semiconductor photocatalysts by calculating the physical properties,agreeing with the experimental results.We obtained a new descriptor for HER by studying the non-metallic element doping of g-C3N4.The descriptor for the activity of electrocatalytic hydrogen production present a guiding role,which is consistent with the experimental results.