Hydrothermal Synthesis And Electrochemical Properties Of 1T-MoX₂（X=S、Se）

Two dimensional(2D)transition metal dichalcogenides(TMDs),such as molybdenum disulfide(MoS2),molybdenum diselenide(MoSe2),have attracted much attention,which is ascribed to the numerous crystal structures to cause different physical and chemical properties.Two typical crystal structures,triangular prism coordination with semiconductoring phase(2H)and octahedral coordination metallic phase(1T),have been studied for last decades.Compared with 2H-MoX2(X=S、Se),1T-MoX2(X=S、Se)have larger layer spacing,higher conductivity and better hydrophilicity.Therefore,1T-MoX2(X=S、Se)have the potential to be excellent electrochemical electrode materials.However,1T-MoX2(X=S、Se)also possess higher formation barrier and show thermodynamic metastable,resulting to synthesizing difficulty and transforming to 2H phase easily.The synthesis of 1T-MoX2(X=S、Se)can be summarized as top-down regulation and bottom-up design.In addition,hydrothermal synthesis,as a common nanotechnology to prepare nanomaterials,is widely applied because of its many controllable factors,simple operation,and good uniformity of samples.Therefore,the high ambient-stable 1T-MoX2(X=S、Se)can be prepared by controlling various factors of the hydrothermal method.In this paper,highpurity and high-stability 1T-MoX2(X=S,Se)are prepared by regulating the hydrothermal synthesis from the external environment and the internal structure,including pH,vapor pressure of the reaction system,the employ of hard template.The mechanism of hydrothermal synthesis is analyzed based on characterization in detail.Finally,the electrochemical property is tested to provide the theoretical basis for practical application.The main contents of this paper are as follows:Firstly,considering the different atomic radius of Mo and W atoms,the microstrain can be obtained by hydrothermal synthesis when part of the atomic positions of Mo are occupied by W atoms,which promotes the phase transformation of MoS2.1TMo0.71W0.29S2 is obtained through W doping on carbon cloths by one-step hy drothermal synthesis.Additiaonally,a series of samples for Co-(1T-Mo0.71W0.29S2)-x%(x=0,0.5,1,1.5,3,5,10)on carbon cloths are synthesized after transition metal Co doping.Co(1T-Mo0.71W0.29S2)-1%(abbreviation:MWC-1%)has the best supercapacitor performance(1235 mF cm-2 at 2 tA cm-2).Secondly,S and Se atom have the same outermost electrons but different atomic radius.Se sites are occupied by S atoms through hydrothermal synthesis,forming microstain to obtain high-purity 1T phase MoSe2.1T-MoSe1.44S0.56 is synthesized after S-doped by one-step hydrothermal synthesis.1T-MoSe1.44S0.56 showes excellent supercapacitor and hydrogen evolution reaction performance as compared with 2HMoSe2,such as a specific capacitance of 20 F g-1 at 2 A g-1,low overpotential of 167 mV at 10 mA cm-2 and excellent long-cycle stability.Thirdly,the problem of agglomeration and phase unstability of 1T-Mo0.71W0.29S2 nanosheets is prevented by constructing a 1T-Mo0.71W0.29S2/Ti3C2Tx MXene heterostructure.Under the hydrothermal synthesis,a heterostructure of 1TMo0.71W0.29S2/Ti3C2Tx MXene with high phase stability was synthesized by the confinement growth and skeleton action for template of Ti3C2TX MXene.Moreover,the effect of different amounts of Ti3C2T,MXene on the whole sample is studied,and it is found that only 1T-Mo0.71W0.29S2/Ti3C2Tx MXene-110(abbreviation:1T-MWS/Ti3C2Tx MXene-110)with an appropriate amount of Ti3C2Tx MXene possesses most excellent supercapacitor performance under the synergistic effect(284 F g-1 at 1 A g-1).Finally,1T-MoS2 is synthesized under the assistance of the synergistic effect of nitric acid(HNO3)and alcohol(CH3CH2OH)by one-step hydrothermal synthesis.The concentration of 1T phase reached to 83.6%.MoO3 with the same crystal structure as 1T-MoS2 is obtained by the chemical reaction HNO3 and the molybdenum source.CH3CH2OH can increase the vapor pressure of the hydrothermal reaction.Under the combined effect of the two,1T-MoS2 is successfully prepared.In addition,the specific capacitance of MoS2(Synergism)as an electrode material is 392 F g-1 in 1 M sodium sulfate(Na2SO4)for supercapacitors.