Preparation And Supercapacitive Properties Rearch Of Molybdenum Based Composite Electrode Materials

Increasing energy demand and worsening environmental problems have stimulated the rapid development of new renewable energy storage devices.Supercapacitors,as a new type of energy storage device which is different form conventional capacitors and chemical batteries,have the advantages of abundant raw materials,high power density,long cycle life,rapid charge and discharge,and environment friendly,which are expected to be widely used in vehicle,military,aerospace fields.As a kind of electrode material for pseudocapacitance of supercapacitors,transition metal molybdenum-based compounds have become potential electrode materials for research due to its high specific capacity and energy density.However,it still has inferior characteristics such as low conductivity and cyclic stability.On the contrary,oxidation graphene with the high surface area and chemical stability show excellent cyclic stability and high conductivity,but the lower specific capacity hinder its further development.Therefore,further exploration and development of molybdenum-based and carbon-based electrode materials with higher specific capacity and better cyclic stability to improve the electrochemical properties of supercapacitors are of great significance.In this paper,we designed and prepared high-performance molybdenum/graphene composites electrode by combining the advantages of molybdenum based materials and oxidation graphene in order to improve the specific capacity and cyclic performance of the composites.The microstructure and material composition of the composites were analyzed by SEM,TEM,XRD and XPS.The electrochemical properties were tested by cyclic voltammetry,electrochemical impedance and constant current charging-discharging.This research is beneficial to the development of molybdenum electrode materials in the field of supercapacitors.The main contents and conclusions are as follows:（1）CoMoS@rGO/NF composites with flower-like microstructure were successfully prepared on reduced graphene oxide/Ni foam（rGO/NF）substrate by two-step hydrothermal method.It is found that vulcanization has a great effect on the morphology and pseudo capacitance for the composites.After three hours of sulfurization,the CMS-3@rGO/NF composite shows the best electrochemical performance,including a large specific capacitance of 2530.4 F g^-1 at 1 A g^-1 and high capacitance retention over 78.8%(at 10 A g^-1)after 6000cycles.In addition,the assembled asymmetric device CMS-3@rGO/NF||AC delivers a high energy density of 59.0 Wh kg^-1 at a power density of 640 W kg^-1,and it still retain 25.2 Wh kg^-1 even at 8960 W kg^-1.The device still holds 90.7%of the initial capacitance after 6000 successive charge-discharge cycles,showing excellent structural stability and electrochemical performance.（2）The core/shell CoMoO₄@CoS comosites have been successfully synthesized on rGO/NF substrate via hydrothermal and electrochemical deposition method.Firstly,the morphology and electrochemical properties of CoMoO₄,CoS and CoMoO₄@CoS composites were investigated.It shows that the CoMoO₄@CoS composite has a more stable core/shell structure and higher specific capacitance than that of single CoMoO₄ and CoS.Secondly,different electrochemical properties of CoMoO₄@CoS composites were obtained by controlling loaded CoS mass.The CoMoO₄@CoS composite with the CoS mass of 0.5 mg shows clearly superior electrochemical properties compared with that of the other samples which have different CoS mass in this experiment.It exhibits a specific capacitance of 3380 F g^-1 at a current density of 1 A g^-1.In addition,the asymmetrical supercapacitor device composed of CoMoO₄@CoS||AC delivers higher specific energy density of 59.2 Wh kg^-1 at a power density of799.8 W kg^-1 and excellent cycling stability（a capacitance loss of only around7.3%after 6000 cycles）,exhibiting excellent electrochemical properties and cyclic stability.（3）The NiMoO₄@Co₃O₄ composite was prepared by two step hydrothemal methods on rGO/NF.The influence of the hydrothermal reaction time on the electrochemical properties of the composites was investigated by changing the reaction time.The combination of NiMoO₄,Co₃O₄ and rGO not only contributes to the improvement of the structural stability of the composite,but also plays a positive role in improving the electrochemical properties.After five hours of reaction,the NiMoO₄@Co₃O₄ composite shows the best electrochemical performance.At a current density of 1 A g^-1,it delivers a spcific capacitance of1722 F g^-1,which is about 3.8 times better than that of the single NiMoO₄electrode.It is worth mentioned that the cycle retention rate and coulombic efficiency of the supercapacitor assembled by the composite are both 100%after 4000 cycling,showing excellent cycling performance.