Pseudocapacitance Behavior Of Transition Metal Sulfides Hollow Nano-structures And Their Arrays

With the increasing demand for energy storage technologies, supercapacitors have attracted enormous research attention due to their high energy density compared with traditional physical capacitors and high power density compared with rechargeable batteries. Supercapacitors are projected to be one of the best potential candidates’ applications for energy conversion and storage systems. Note that electrode materials have become the core components to supercapacitors. To meet the increasing demands for reliable efficient supercapacitors, the development of new promising materials with high energy storage still remains essential and pressing. Therefore, based on the Kirkendall effect prepared transition metal sulfide hollow and array structures with a good electrical conductivity, fast ion diffusion path and rich redox and excellent electrochemical performances were carried out in this dissertation. At first, hollow nanostructures and composite arrays of transition metal sulfides were designed and controlled synthesized. Then, the formation mechanism and charge storage mechanism of the transition metal sulfides nanostructures and composite arrays were extensively investigated. Finally, the excellent hybrid supercapacitors were encapsulated using the above hollow metal sulfides with the best electrochemical performance. The main results were outlined as following:The cobalt sulfides hollow nanotubes and their arrays were controlled synthesized based on the Kirkendall effect. The formation and charge storage mechanism of hollow cobalt sulfides were systematically analysed. The Co9S8hollow nanotubes with diameter of approximately250nm, a length of about3μm were prepared using one-dimensional Co-salt precursor nanorods as sacrificial template. The different nano-sizes of Co9S8hollow nanotubes were prepared by controlling the reaction temperatures of the precursor. The Co9S8nanotubes exhibit capacitance performance superior to Co3O4nanorods benefited from its high conductivity, electrochemical activity of ion diffusion channel. The Co9S8nanotube obtained at80℃with high specific surface area and the optimal electrolyte ion diffusion path and electrochemically active site so that it has a relatively high capacitance performance, the specific capacitance reached285F g"1at a current density of0.5A g-1. On this basis, the Co9S8hollow nanotube arrays were grown on surface of FTO and the graphene paper, the composite electrode materials show excellent capacitive properties due to the special ion diffusion path and the electron conduction.The Ni-Co sulfides hollow nanotubes and their arrays were designed and controlled synthesized. The formation and charge storage mechanism of hollow nickel cobalt sulfides were systematically analysed. The Ni-Co sulfides hollow nanotubes were prepared using of urchin-like Ni-Co precursor salt as sacrificial template. The different of Ni/Co ratio sulfides with different structures were obtained by controlling the Ni/Co ratio of Ni-Co sulfide precursor. The capacitive performances NiCo2S4nanotubes exhibited better than NiCo2S4nanorods and NiCo2O4nanorods owing to high electronic conductivity, excellent electrochemical activity, and having fast ion diffusion channel. The capacitance of NiCo2S4nanotubes exhibited have1145F g’1at0.5A g-1. The capacitive performances Ni/Co(1:2) sulfide exhibit higher than other ratios on the account of richer and more active redox reactions. On this basis, the three-dimensional NiCo2S4nanotubes@Ni-Mn LDH/graphene sponge electrode material were constructed, which possess1740.3mF cm-2at1mA cm-2, and exhibiting excellent rate capability and cycle stability.The hedgehog-like hollow Ni-Mn precursor with uniform ordered one-dimensional nanostructure was prepared. The formation and charge storage mechanism of hollow Ni-Mn sulfides were systematically analysed. Firstly, the directional Mn-induced approach of hedgehog-like hollow nanostructure was confirmed based on TEM, SEM, XRD, FT-IR characterizations of the different reaction time products. Secondly, the Ni-Mn compounds (oxides, hydroxides, sulfides) were obtained by annealing at different temperature, hydrothermal at different concentrations of NaOH, Na2S aqueous solution from hedgehog-like hollow Ni-Mn precursor. The hollow Ni-Mn sulfide showed the higher electrochemical performance than hollow Ni-Mn oxides, hydroxides due to high electrical conductivity and electrochemical activity. Finally, the secondary hollow structure Ni-Mn sulfides were obtained by controlling the reaction of S2-concentration. The secondary hollow Ni-Mn sulfides achieved high specific capacitance of1530.1F g-1at0.5A g-1, attributed to the high electron conductivity, fast ion diffusion channel and active redox reaction.The encapsulation technologys of a different set of asymmetric supercapacitor were extensively investigated. The above high performance capacitance NiCo2S4nanotubes as a cathode material and activated carbon as the anode material encapsulated into NiCo2S4//AC hybrid supercapacitor. The NiCo2S4//AC hybrid supercapacitor emerged excellent capacitance performance in the temperature range of10-90℃, exhibiting high energy density and power density. While relatively inexpensive secondary hollow structure Ni-Mn sulfide as a cathode material and the activated carbon as anode material encapsulated into Ni-Mn sulfide//AC asymmetric supercapacitor, which can exhibit mixed with NiCo2S4//AC unmatched energy density and power density. In addition, the three-dimensional NiCo2S4@Ni-Mn LDH/graphene as a cathode material, VN/graphene as a negative electrode material encapsulated into asymmetric supercapacitors, which exhibit excellent energy density and power density.Controlled preparation, formation mechanism and charge storage mechanism of ultra high specific capacitance transition metal sulfide hollow structures as electrode materials for electrochemical supercapacitors were systematically analysed. This investigation will provide technical and theoretical support for the further development of high performance reversible energy storage device and high specific power energy storage system. Therefore, all researches will lay the foundation of next-generation energy stroage devices fundamental and appliation fields.