| In order to meet the increasingly urgent energy demand,the development of high-efficiency and pollution-free energy storage and conversion devices has become the top priority of research in recent years.With many advantages such as excellent cycle performance,high power density,rapid charge/discharge behavior and low maintenance costs,supercapacitors have become a promising choice among many new energy storage devices.Electrode materials are most important components that affect the energy storage performance of devices,so the design and preparation of electrode materials is a key part of manufacturing high-performance supercapacitors.Among the many transition metal compounds,the molybdenum-based monometallic oxide（sulfide）has a high theoretical specific capacity,abundant redox sites,and abundant and cheap preparation materials,making it a kind of pseudocapacitance electrode material with great development potential.But it is still limited by low intrinsic conductivity and poor cycle stability.To this end,this thesis takes the improvement of specific capacity and improvement of cycle stability as the starting point,the molybdenum-based bimetallic oxide（sulfide）is prepared by a simple and environmentally friendly hydrothermal method,and the sample structure and its application performance in supercapacitors are evaluated.The high electrochemically active metal elements（Co and Ni）introduced therein not only provide abundant active sites,but the synergistic effect of the two metal ions greatly increases the conductivity of the compound.Furthermore,substituting S element with lower electronegativity for oxygen can increase the electrical conductivity and at the same time increase the flexibility of the structure,which is beneficial to improve the cycle stability.The specific research content is as follows:（1）Using Ni foam（NF）as the substrate,the Co Mo2S4 nanorod electrode material with rough surface was successfully synthesized by the two-step hydrothermal method,and the material structure and electrochemical performance were optimized by controlling the vulcanization temperature.Electrochemical tests show that the Co Mo2S4 electrode exhibits the best performance when the vulcanization temperature is 120℃,and its specific capacitance reaches 1992.85 F g-1(current density is 2 m A cm-2).At the same time,good cycle stability is achieved.After 8,000 cycles of continuous charging and discharging,the specific capacitance increases to 106%of the initial value.In addition,the energy density of the hybrid supercapacitor constructed with Co Mo2S4 and AC as positive/negative electrodes reached 39.8Wh kg-1(power density was 600 W kg-1);after 5000 cycles,the capacitance retention rate was83.43%.（2）The NiMoO4/ZnMoO4 composite electrode material was successfully prepared by the hydrothermal-annealing method with NF as the substrate.The research shows that the annealing temperature and the Zn:Ni ion ratio have a significant effect on the capacitance performance of the material.At an annealing temperature of 450℃and Zn:Ni=4:4,the NiMoO4/ZnMoO4composite electrode exhibits the highest specific capacitance(2064.07 F g-1 at 2 m A cm-2);It exhibits excellent cycle stability（retaining 99%of the initial capacitance after 10,000 cycles of continuous charging and discharging）.The assembled NiMoO4/ZnMoO4//AC device shows a maximum energy density of 47.4 Wh kg-1;and after 12,000 GCD cycles,the specific capacitance retention rate can still maintain 91.74%of the initial specific capacity.（3）The NiMoS4/ZnMoS4 composite electrode material was directly grown on the NF substrate by the two-step hydrothermal method,and the relationship between the vulcanization temperature and the electrochemical performance was studied.With the increase of the vulcanization temperature,the specific capacitance value of the electrode material first increases and then decreases,reaching the best value at 120℃.The specific capacitance reaches2407.84 F g-1 at 2 m A cm-2;it still has a capacity retention rate of 87.6%after 10,000 cycles(the current density is 40 m A cm-2).Furthermore,the asymmetric device is assembled with NiMoS4/ZnMoS4/NF as the positive electrode and AC as the negative electrode.It has an energy density of 54.26 Wh kg-1 and a power density of 8947.37 W kg-1.After 10,000 charge and discharge cycles,the capacitance retention rate is 97.39%. |
