Controllable Preparation And Energy Storage Applications Of Graphene/Carbon Nitride Hybrids

With the development of new energy storage devices,to exploit high-performance electrochemical energy storage devices with high energy and power density has attracted extensive attentions from scientists and engineers.The main challenge is to design and fabricate electrode materials with short charge transport length,high specific capacity and fast redox reaction process.In this dissertation,based on the self-assembly and capillary shrinkage of graphene,we have proposed and designed graphene/g-C₃N₄hybrids with a combined structure of three-dimensional（3D）network and two-dimensional（2D）nanosheets as high-performance electrode used in electrochemical energy storage devices.Firstly,in the preparation of graphene and g-C₃N₄ hybrids,3D graphene network and urea,as the g-C₃N₄ precursor,are used as the mutual templates.On one hand,urea,statically adsorbed into graphene hydrogel,is firstly used as the“spacer”for controlling the shrinkage of the graphene network during the capillary drying process.On the other hand,the 3D graphene network helps to uniformly disperse the urea and thus produce unstacked and porous g-C₃N₄ nanosheets within the pores of the graphene network.Then,the removal of g-C₃N₄ from 3D graphene network can achieve controlled nitrogen doping with a further heat treatment.Secondly,g-C₃N₄ can propel the transformation of lithium polysulfides（LiPSs）by catalytic effect in lithium-sulfur batteries.The formation of interlayer bonds ensures an intimidate contact between g-C₃N₄ and graphene.Consequently,the“shuttle effect”of LiPSs is largely suppressed by the synergistic process of anchoring and catalyzing the fast conversion of soluble LiPSs within the spatial pore confinements,delivering an excellent cycling performance for sulfur cathode in lithium-sulfur batteries.Overall,this thesis fabricates the hierarchically structured 3D non-polar graphene network and 2D polar g-C₃N₄ nanosheets hybrids,which is instructive for constructing redox reaction framework to promote electrochemical reaction redox kinetics.