Theoretical Study On The Regulation Of Polarized Electric Field On The Photolytic Water Performance Of Z-Scheme Heterostructures

With the excessive consumption of fossil fuels,environmental pollution and resource shortage are becoming increasingly prominent.Therefore,it is extremely urgent to explore renewable energy resources.Photocatalytic water splitting has attracted extensive attention because of its ability to achieve solar to hydrogen energy conversion,which is a clean,green,safe,stable,and promising technology.However,currently photocatalysis technology is still limited by a low catalytic efficiency,and various methods have been adopted to improve the efficiency.Among them,the feasible and favorable method is to construct heterostructures.According to the band alignments of the heterostructures,they can be divided into type-Ⅰ,type-Ⅱ and type-Ⅲ.Although type-Ⅱ heterostructure can promote the separation of photogenerated carriers to some extent,their redox abilities are weakened.Fortunately,the Z-scheme heterostructure is one ideal configuration,which can efficiently separate the photogenerated carriers between layers and maintain their strong redox abilities.Meantime,the polarized materials can break the band gap limit of 1.23 e V and the polarization electric field is also a powerful driving force to separate photogenerated carriers with in the layer.In this thesis,density function theory is used to study the regulation of polarization electric fields on the photocatalytic water splitting performance of Z-scheme van der Waals heterostructures.Z-scheme heterostructures containing polarization materials,with the dual advantages of polar materials and Z-scheme heterostructures,we explored in detail their significant advantages and enormous potential in water splitting,which effectively enhance the activity of photocatalysts.The specific research work is as follows:1.We designed a Z-scheme g-C₆N₆/InP heterostructure composed of polarized materials by first-principles calculations.The intrinsic dipole moment of InP generated a polarization electric field,which can lead to the deviation of the oxidation reduction potential of water.This is conducive to the recombination of holes on InP with electrons on g-C₆N₆,leaving holes and electrons on g-C₆N₆ and InP,respectively.According to the Gibbs free energy calculation,the g-C₆N₆/InP heterostructure under neutral and light conditions,and oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）occurring on the g-C₆N₆ and InP,respectively.Meanwhile,the solar energy conversion efficiency can reach 21.69%.Based on these findings,the g-C₆N₆/InP heterostructure is a potential Z-scheme photocatalysts.2.In the Z-scheme heterostructure composed of polar materials,there exist both polarized and interface electric fields,and different electric field directions can lead to different photocatalytic performances.Therefore,we investigated the performance differences of heterostructure in photocatalytic water splitting under the combined action of different polarized and interfacial electric fields.By studying six different GeC and SnS configurations,it was found that the polarized and interfacial electric fields remain consistent when the Sn atomic surface is adjacent to GeC,and the AB（Sn）-2 configuration is a direct Z-scheme heterostructure.Under illumination,the AB（Sn）-2 configuration can spontaneously photocatalytic overall water splitting,with HER and OER occurring on GeC and SnS monolayers,respectively.When the S atom is adjacent to GeC,the polarized and interfacial electric fields’directions are inconsistent.The AB（S）-2configuration is a type-Ⅱ heterostructure,which can only spontaneous HER on the SnS monolayer.In addition,we also investigated the effects of electric field coupling within heterostructure on their bandgap,electrostatic potential difference,dipole moment and light absorption capabilities.We found that the AB（S）-2 configuration has strong light adsorption ability and high solar energy conversion efficiency（23.94%）.3.The Z-scheme heterostructure constructed by polar materials can effectively achieve photocatalytic overall water splitting,but the structural deformation of pristine non-polar materials can also generate polarized electric fields.Therefore,we also explored the photocatalytic water splitting performance of the heterostructure constructed from non-polar materials.We design a two-dimensional CdS/SnS₂heterostructure with different configurations and investigate the electronic band structure,charge separation efficiency,as well as photocatalytic properties by first-principles calculations.In the CdS/SnS₂-（Ⅰ,Ⅱ）configurations,the polarized electric field is induced by the displacement of Cd and S atoms.Under the combined action of interface and polarized electric field,electrons on the conduction band（CB）of CdS transfer to the CB of SnS₂,while holes on the valence band（VB）of SnS₂ migrate towards the VB of CdS.Therefore,the CdS/SnS₂-（Ⅰ,Ⅱ）configuration from type-Ⅱ heterostructures,but the band edge position cannot satisfy the overall water splitting requirement.However,it is absent in the CdS/SnS₂-Ⅲ configuration with a stronger oscillation of S atoms located on both Cd sides.Based on the staggered band alignment and electron transfer direction,the CdS/SnS₂-Ⅲ configuration exhibits a direct Z-scheme feature.Moreover,the HER and OER can take place simultaneously on the CdS and SnS₂ layers in the CdS/SnS₂-Ⅲ configuration under illumination,respectively.In addition,the high solar-to-hydrogen（STH）efficiency of the CdS/SnS₂Z-scheme heterostructure,up to 31.73%,is attributed to the strong visible light harvesting capability and excellent photogenerated carrier separation.