Synthesis And Supercapacitor Performances Of Two-dimensional Transition Metal Carbonitrides And Related Heterostructures

Concept of two-dimensional materials has been proposed and attracting tremendous research attention since the successful exfoliation of monolayer graphene from bulk graphite by Andre Geim and Konstantin Novoselov using micromechanical cleavage method in 2004.Recently,two-dimensional transition metal carbides and carbonitrides(MXenes)have been emerging as a new family of two-dimensional materials and causing wild research enthusiasm.MXenes are endowed with great properties,such as chemical stability,high intrinsic conductivity,remarkable mechanical strength and hydrophilic surfaces.Thus,they are considered as one of the most promising next-generation substitutes to graphene in energy storage applications.With high intrinsic conductivity,MXene nanosheets can provide fast charge transfer pathways,thus helping to enhance the conductivity and electrochemical performance when serving in nanocomposites.Therefore,MXenes and their related heterostructures indicate great potential for constructing high-performance electrode materials.Based on this research background,we conducted this research on“The synthesis and supercapacitor performances of two-dimensional transition metal carbonitrides and related heterostructures”.Our research work mainly involves in the following three aspects:(1)We chose bulk Ti₃Al C₂ as MAX phase precursor,taking a one step in-situ HF formation method to prepare the MXene phase Ti₃C₂T_x.Avoiding of high concentration HF usage reduces the risk of experiment.The lithium ions intercalating between Ti₃C₂T_x layers during synthesis process would enlarge the interlayer spacing,which can serve as intercalant and lead to the direct exfoliation after etching process.Structural characterizations were further conducted for the prepared two-dimensional Ti₃C₂T_xnanosheets to reveal their high quality.(2)For the as-prepared Ti₃C₂T_x,we took a one-step hydrothermal treatment to grow Mo S₂nanosheets on its surface,constructing a mixed-dimensional heterostructure between Mo S₂ and Ti₃C₂T_x.Via this method,Mo S₂can be vertically aligned and interconnected with each other,forming a network structure and wrapping up the entire surface of Ti₃C₂T_x.This morphology was constructed to increase the exposure of electrode materials to the electrolyte,thus improving the contact extent.We took Ti₃C₂T_x as the matrix for Mo S₂because of its stability and high conductivity,in order to overcome the intrinsic disadvantages of Mo S₂.Results indicate that the introduce of Ti₃C₂T_x has effectively alleviated the aggregation of Mo S₂and improved its conductivity.The Mo S₂-Ti₃C₂T_xheterostructure exhibits much enhanced supercapacitor performance,achieving a huge promotion compared to pristine Mo S₂ and Ti₃C₂T_x.Meanwhile,this heterostructure material also shows great rate performance and long-term cyclic stability.(3)Hydrothermal treatment was taken to construct heterostructures between Ti₃C₂T_x and Ni,Co-LDH.LDH sheets form a network structure and strongly interact with Ti₃C₂T_x.The fast charge transfer ability of Ti₃C₂T_x will help to break the bottleneck of LDH,solving the problem of dramatic capacity decay when serving in high current density.Introduction of Ti₃C₂T_xcan reduce the internal resistance of the heterostructure and improve the ion exchange between electrode and electrolyte.Electrochemical tests indicate that Ti₃C₂T_x/Ni Co-LDH shows great improvement in rate performance and cycling stability while preserving the high specific capacity of pristine Ni,Co-LDH at the same time.It is also found that a 26%mass fraction of Ti₃C₂T_xbrings with the best overall electrochemical performance.