Preparation And Electrochemical Properties Of Molybdenum Based Supercapacitor Electrode Materials

With the rapid economic development,fossil fuels with highly polluting energy sources are being consumed at an alarming rate.The development of advanced energy conversion and storage technology plays an important role in maintaining the balanced development of global economy.Among all kinds of energy storage devices,electrochemical energy storage devices（lithium-ion batteries,fuel cells,super capacitors）are the most widely used.Supercapacitor is a new kind of energy storage device which is environmentally friendly and highly efficient.It has a higher energy density than conventional capacitors and a higher power density than rechargeable batteries.However,the high energy density of supercapacitors can not meet the practical application.One of the effective ways to solve this problem is to develop high performance electrode materials.At present,transition metal compounds are widely used in high performance supercapacitors due to their abundant sources and low cost.Among them,molybdenum-based compounds have different chemical compositions,various valence states and higher theoretical capacitance,which provides more possibilities for the development of new electrode materials.However,it also has the disadvantages of poor conductivity and poor cycle stability,which dramatically limits its practical applications as electrode material for supercapacitors.In this paper,the simple preparation method of molybdenum based electrode materials with high energy storage performance was studied,and the structure,composition,morphology and electrochemical performance of molybdenum based materials were systematically studied.The main work and research achievements are as follows:（1）Mo O₂ was prepared by two-step method and one-step hydrothermal method,respectively.It was found that Mo O₂ synthesized by one-step hydrothermal method had better crystallinity,uniform size distribution of nanostructured structure,and stronger charge storage capacity.（2）Three-dimensional nanoflower-like Mo S₂ was synthesized using（NH₄）₆Mo₇O₂₄·4H₂O as molybdenum source and CH₄N₂S as sulfur source by adding C₂H₂O₄.The specific surface area of the material is increased due to its porous structure,resulting in enhanced charge storage capacity and greatly increased cyclic stability.（3）By only changing the mass ratio of（NH₄）₆Mo₇O₂₄·4H₂O to CH₄N₂S,Mo O₂/Mo S₂ nanocomplexes with different features were obtained.The results show that the composite have higher specific capacity(1667.3F g^-1 at 1 A g^-1 current density)and better cyclic stability（94.75%capacitance retention after 5,000 cycles）.When they are assembled into asymmetric hybrid super electrical devices,the test voltage window can be widened to be 1.8 V,and when the power density is 225 W Kg^-1,the energy density is 21.85 Wh Kg^-1.This work presents a valid technology route to obtain high performance superconductors with simple method.（4）The Ni Mo O₄ precursor was prepared by hydrothermal method and the rod-like Ni Mo O₄ was obtained by annealing at high temperature.The rod-like structure can not adapt well to the material volume change during charging and discharging.The flower-like Ni Mo O₄/Ni O nanocomplexes with different porosity were obtained by adding CH₄N₂O with different mass ratios.For the asymmetric hybrid supercapacitor assembled with Ni Mo O₄/Ni O as positive electrode and AC as negative electrode,the test voltage window can be widened to 1.9 V,and when the power density is 264.67 W Kg^-1,the energy density is 14.39 Wh K^-1,which possesses good electrochemical performance.