Theoretical Study And Design Of Single Atomic Electrocatalysts Supported By Graphene Capsules

In recent years,problems including modern society’s increasing demand for energy,shortage of fossil fuels and atmospheric pollution have promoted people to turn their at-tention to clean hydrogen energy.Hydrogen production by electrolysis of water is a more convenient way to produce hydrogen.The hydrogen evolution reaction(HER)catalyst with high efficiency,environmental protection and low price can reduce the high energy consumption needed in the production,improve the efficiency and promote its wide ap-plication.In this aspect,single atom catalysts with high catalytic activity can maximize catalytic efficiency.On the other hand,the graphene capsule is a new type of carbon na-nomaterial,which has been found to have excellent application prospects as a catalyst substrate.Therefore,the research topic of this thesis is the application of graphene cap-sules in single atom catalyst through first-principles calculations,carrying out theoretical research about its hydrogen evolution performance after Pt adsorption.It is committed to the design of both structural stability and catalytic performance of HER electrocatalyst.We first perform extensive studies on the modeling of the graphene capsule,as well as its stability and electronic properties.With hydrogen evolution free energy as the main parameter,the HER performance of single Pt atom on the graphene capsule as an electro-catalytst is studied.The single Pt atom adsorbed both inside and outside the graphene capsule has good hydrogen evolution performance which can be compared with that on the surface of the Pt(111).It is considered that appearing certain curvature,with appro-priate combination of the pentagonal and hexagonal carboatomic ring,triggers the hy-bridization between C’p_z orbital and Pt atoms’d states,leading to different effects of hy-drogen evolution.Further calculation was carried to simulate the common point defects in carbon ma-terials,B,N and O doping in the system,and their influence on HER.The introduction of point defects on graphene capsules has little effect on hydrogen evolution,but can further improve the adsorption stability of the Pt atom.The catalytic performance of the system when Pt is inside can be further improved by doping B or N atoms,while O doping,by changing the shape of the capsule and the hydrogen bonding of oxygen to hydrogen,has an excellent active site for hydrogen evolution when Pt is outside.Then promote single Pt atoms to generalized ones,namely small Pt clusters,study its HER performance effect in the capsule which plays as a core-shell structure.The catalytic activity of HER can also be raised with the internal catalyst being protected.In conclusion,graphene capsules can be used as the substrate for the HER catalyzed by Pt atom,which has excellent catalytic activity for HER both inside and outside the capsules.The innovation of this thesis is that the internal mechanism of catalyst perfor-mance difference is revealed through the analysis of electronic properties and orbital hy-bridization.The thesis can provide necessary theoretical guidance for the experimental design of new electrocatalytic HER catalysts,which are expected to improve the reaction rate and realize the rapid and low energy consumed electrolysis of water to produce hy-drogen.