Research On Structure Regulation Of Graphene-based Functional Composites And Their Application In Electrochemical Energy System

Aiming at the problems of sheet stacking,inert surface and poor longitudinal mass transfer of graphene materials,this thesis uses multidimensional assembly,heteroatoms doping,and in-plane pore formation to conduct intrinsic and macro structures regulation of graphene.Then,guided by practical application and functionalization,graphene/metal-based functional nanocomposites that spans four dimensions of"atomic-nano-micro-macro"were designed and prepared.The performance of the nanocomposites in the electrochemical energy system were studied.The main achievements of the dissertation were as follows:1.The intrinsic structure regulation of graphene:Two-dimensional porous N,S Co-doped graphene nanosheetsThe intrinsic structure of graphene was regulated by heteroatoms doping and in-plane pore creating.Using organic molecules as precursors,a two-dimensional porous N,S co-doped graphene supported single Fe atom catalyst was prepared by polymerization assembly,template method and carbon thermal reduction.The material has high specific surface area,high electrical conductivity,rich porous structure,high nitrogen and sulfur element doping amount,and high-load uniformly dispersed single Fe atom.Doped sulfur and Fe atoms form a new type of Fe-N₃S coordination structure.Electrochemical test results show that the catalyst exhibits excellent electrocatalytic activity for oxygen reduction reactions,much higher than traditional Fe-N₄ catalysts and commercial Pt/C catalysts.The zinc-air battery assembled with the catalyst also exhibited excellent performance.2.The macro structure regulation of graphene:Three-dimensional porous graphene foamThe macro structure of graphene was regulated by three-dimensional assembly.A new method based on low-temperature spontaneous reduction of graphene oxide and assembly on nickel foam surface was developed to build three-dimensional graphene foam(GF).Co Mo O₄ and Fe₂O₃ nanosheet arrays were grown with on GF,and then hydrogenation treatment to constructed two new types of graphene/oxygen-deficient metal oxide composite electrodes with hierarchical porous structure.Due to the synergistic effect of porous structure,large specific surface area of the three-dimensional graphene foam,the fast mass transfer rate brought by the three-dimensional conductive network structure and the metal oxide nanosheet arrays structure,and the electronic structure and pseudocapacitance performance improved by oxygen defect,Both the electrodes and the flexible all-solid-state supercapacitors based on them show excellent energy storage performance and cycle stability.3.The intrinsic and macro structures regulation of graphene:Three-dimensional porous vertically aligned N-doped graphene nanomesh arraysThe intrinsic and macro structure of graphene was regulated simultaneously by in-plane pore creating,heteronuclear doping and three-dimensional assembly.A novel type of three-dimensional porous vertically aligned N-doped graphene nanomesh arrays(VNGNMAs)material was designed and developed for the first time via a facile and well-controlled combination of polymer self-assembly and self-sacrifice template methods.Based on the real-time observation by in-situ transmission electron microscopy,we propose a versatile template diffusing-disembedding-graphitizing mechanism for the formation of holes and graphene in VNGNMAs.As-obtained material possesses several unique features,such as vertically oriented graphene nanomeshs,large pore volumes,3D interconnected conductive networks,high specific surface area and abundant N binding sites.It is a major breakthrough to solve three scientific problems existing in graphene materials.Subsequently,the VNGNMAs was used as the carrier to modify the metal-based nanocomponents,including Pt nanoparticles,single Pt atoms,manganese oxide nanoflakes,molybdenum sulfide nanoflakes.A series of functional nanocomposite materials were developed and applied in the fields of electrocatalytic hydrogen evolution,flexible all solid state supercapacitors,lithium-ion batteries,which showed excellent electrochemical performance.The new graphene material has great beneficial effects on improving the high load of active materials,promoting the rapid transport of ions and maintaining the structural stability.