| Supercapacitors have attracted extensive attentionfrom both research and industry due to their advantages of high power density,long cycle life,fast charging,safety and environmental sustainability.However,compared with secondary batteries,the energy density of commercial supercapacitors is still lower,which limits their further applications in various fields.The electrode materials are a key factor that determines the performance ofsupercapacitor systems.Previous studies show that transition metal phosphides/boridespossess metal-like properties,such as higher conductivity and better electrochemical activity.Therefore,transition metal phosphorus/borides are often used as electrode materials,and their superior electrochemical performance is fully exploited by rational design of their composition and structure.In this thesis,the idea of electrode design is featured by the following two aspects.(1)Composition:multi transition metal phosphides are generated by the synergistic effect of multi metals.(2)Structure:the core-shell nanowire-like architecture is constructed to increase the number of reactive sites,so as to improve the electrochemical performance,as well as the energy density of the supercapacitors.The research contents and main results of this thesis are summarized as follows:(1)The NiCo-P@CoNiMo-P core/shell nanowires structure grown on foam nickel was successfully designed and synthesized by the two-step hydrothermal phosphating method.The electrochemical properties of the Co,Ni,and Mo components can be complementary to one another,and the addition of various metal elements can increase the number of reactive sites,thus improving the pseudocapacitance.The hollow spaces between the core/shell nanowires structures are conducive to the full contact of electrolyte ions with the "core" and "shell" structures,which provides the structural conditions favorable for the electrode materials to fully react with electrolyte ions.The electrode material has a specific capacity of 1366 C g-1 at 2 A g-1,and a specific capacity of 922 C g-1 at 10 A g-1.We use the NiCo-P@CoNiMo-P as the positive electrode and the N-rGOs as the negative electrode to assemble a hybrid supercapacitor.,The energy density of this supercapacitor can reach 81.4 Wh kg-1 at the power density of 1213 W kg-1.It also exhibits a capacity retention of 132%after 6000 cycles at a current density of 10 Ag-1.This work provides new insight for the rational design and preparation of transition metal phosphide cathode materials for supercapacitors.(2)The self-supporting NiCo2O4@NiCo-B core/shell nanowires structure was successfully prepared through hydrothermal,high-temperature annealing and boronization treatment.NiCo2O4 itself has a high theoretical capacity,and the introduction of boron is conducive to the electron transfer and redox reactions.The core/shell nano wires structure can provide more active sites,thereby significantly improving theelectrochemical performance.The as-prepared electrode material has a specific capacity of 1009 C g-1 at 1.5 A g-1 and a specific capacity of 750 C g-1 at 10 A g-1,thus exhibiting excellent rate performance.The NiCo2O4@NiCo-B and N-rGOs electrode materials are used as the positive and negative electrodes to assemble a hybrid supercapacitor.This supercapacitor delivers a energy density reaching 43.2 Wh kg-1 at the power density of 999.5 W kg-1 with a capacity retention of 93%after 6000 cycles at 10 A g-1.This work opens up a new way to prepare high-capacity cathode materials for new electrochemical energy storage devices. |
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