Fabrication And Electrochemical Property Of Molybdenum Disulfide And Composites

Supercapacitor,also called electro-chemical capacitor,is a new type of energy storage device following the traditional capacitor and battery.The traditional capacitor stores energy through physical mechanism,with the advantages of high power density and cycle stability.But,it has shortcoming of low energy density.The secondary battery has a high energy density due to the adoption of chemical energy storage mechanism,while its disadvantages are narrow working voltage range,low charged-discharged rate and power density.Supercapacitors combine the advantages of traditional capacitor and secondary battery,exploiting the performance of high power and energy density,long cycle life and environmental-friendly.This work studies the preparation methods and electrochemical properties of two-dimensional layered MoS₂ and MoS₂-MWCNT composite,which can be used as an electrode material of supercapacitors.Firstly,sodium molybdate dihydrate?Na₂MoO₄·2H₂O?and thiourea?CS?NH₂?₂?were used as molybdenum source and sulfur source respectively.The flowerlike-sphere MoS₂ was obtained by ordinary hydrothermal synthesis.The appropriate hydrothermal conditions are at 180?reaction temperature for 48 h with the atomic ratio of Mo/S1:4 in a 0.001 mol·L^-1 aqueous solution and the filling volume is 90 mL.Results indicate that the average diameter of as-prepared products is about 1?m with good crystallinity and dispersibility and their specific surface area is about 87m²·g^-1.In order to characterize the electrical properties of MoS₂,the electrochemical performance was studied by CV,GCD and EIS.Results show that in 3 mol·L^-1 KOH electrolyte,the specific capacitance of single electrode is 130.6 F·g^-1(5 mV·s^-1)and110.9 F·g^-1(0.1 A·g^-1).The R_ctt is of 0.33?.The loss of specific capacitance is 14.7%after 1000 cycles.Due to the micro-nano-scale regular morphology and the increasing active sites of larger the specific surface area,the MoS₂ that synthesized by hydrothermal method have nice electrochemical properties.Secondly,Na₂MoO₄·2H₂O and thiourea CS?NH₂?₂ were still used as precursors,and ethanol was used as the solvent of reaction.Pure phase MoS₂ with different morphologys?mesoporous hollow spheres,fungus-like,rose-like and bulbous flower-like?was synthesized through ethanol solvothermal method.The morphology of the products was controlled by reaction temperature and the reaction time.Compared with hydrothermal method,ethanol solvothermal method has the advantages of higher product yield and shorter reaction time.Electrochemical performance tests of these pure MoS₂ with different morphplogy revealed that the performance of products synthesized by ethanol solvothermal is superior to that of hydrothermal method.This can be attributed to the expanding of MoS₂ interlayer spacing by oxygen-intercalated which can accommodate more electrons and ions.In addition,the morphology of MoS₂has a greater influence on the electrochemical properties.The ethanol solvothermal method conditions of mesoporous sphere MoS₂ are at reaction temperature 180?for12 h with the atomic ratio of Mo/S of 1:4 in a 0.001 mol·L^-1 aqueous solution,and the filling volume is 60 mL.These MoS₂ particles own the better electrochemical properties.The specific capacitance of single electrode is 139.8 F·g^-1 at 2 A·g^-11 current density,and the loss of specific capacitance is 11.2%after 1000 cycles.Finally,in order to overcome the semiconductor characteristics of MoS₂ and improve the stability of materials,the MoS₂-MWCNTs composite was prepared by combinating MoS₂ with multi-walled carbon nanotubes.The raw carbon nanotubes were pretreated with concentrated nitric acid ultrasound before the composite.The results showed that the carbon nanotubes pretreated with acidified ultrasound for 8 h were successfully connected with some oxygen-containing functional groups.The MoS₂-MWCNTs composite was synthesized by microwave ethanol solvothermal method.The preferred reaction conditions are as follows:the reaction was carried out at 150?or 180?for 50 min,the concentration of Mo was 2×10^-3 mol·L^-1 and the filling volume was 60 mL.Electrochemical measurement suggests the excellent rate capacities of MoS₂-MWCNTs composite.Their specific capacitance of single electrode reaches 80.4 F·g^-11 at 2 A·g^-1,the interface transfer resistance R_ct is 0.25?and the specific capacitance loss is only 3.3%after 1000 times cycles.The stability of the composites is much better than that of pure phase MoS₂.These results indicate that the MoS₂-MWCNTs composite owns a better electrochemical performance.