Synthesis Of Transition Metal Chalcogenides And Their Applications In Supercapacitors

In this century,the problem of excessive consumption of fossil energy and environmental pollution has become increasingly fierce.Among the developed electrochemical devices for energy storage and conversion,supercapacitors have attracted wide attention because of their fast discharge capacity,long cycle life and high rate performance.Transition metal chalcogenides have attracted wide attention as electrode materials for supercapacitors,but their poor conductivity and cycle stability greatly restrict their applications.Therefore,in order to obtain excellent electrode materials,a variety of materials based on transition metal chalcogenides were prepared and used as high-performance electrode materials in this thesis.This thesis is divided into four parts.After in situ selenylation,hydrothermally synthesized Ni Mo O₄ was partially converted to Ni Se₂ and Mo Se₂,and the obtained Ni Mo O₄/Ni Se₂/Mo Se₂nanowires were used as a supercapacitor electrode material and exhibited excellent electrochemical performance.The high electrochemical performance of the Ni Mo O₄/Ni Se₂/Mo Se₂ can be ascribed to the obvious heterointerfaces,rich defects and remarkably increased electrical conductivity after in situ selenylation of Ni Mo O₄.Hollow nickel-cobalt bimetallic layered hydroxide（Ni Co-LDH）derived from a typical zeolitic imidazolate framework（ZIF-67）was selenized to Ni Co Se₂ via in situ selenylation,which was then coated with a layer of carbon via the hydrothermal method by using glucose as the carbon source.The electrochemical performances of the as-synthesized Ni Co Se₂/C are investigated,and the results indicate that the hollow Ni Co Se₂/C exhibits considerable electrochemical performances.Compared with ZIF-67,Ni Co-LDH and Ni Co Se₂alone,the greatly enhanced electrochemical performances of the Ni Co Se₂/C can be due to the hollow nanostructure of Ni Co Se₂,enhanced electrical conductivity by the introduction of Se and C,and inhibited volume changes during the redox cycling from the protection of the carbon layer.Co Se₂is first synthesized through the selenylation of a typical zeolitic imidazolate framework（ZIF-67）,which is then decorated on the surface of GO via the hydrothermal method.The electrochemical performances of the as-synthesized Co Se₂/GO are investigated,and the results indicate that the Co Se₂/GO exhibits better electrochemical performances.Compared with GO and Co Se₂ alone,the greatly enhanced electrochemical performances of the Co Se₂/GO might be attributed to the synergistic effect of GO and Co Se₂.Reduced Mo-doped Ni Co₂O₄（R-Mo-Ni Co₂O₄）was facilely prepared through the dual-defect strategy.The precursor of Mo-doped Ni Co layered double hydroxide（Mo-Ni Co-LDH）was calcined in air atmosphere,and the resultant Mo-doped Ni Co₂O₄（Mo-Ni Co₂O₄）was further reduced by Na BH₄.The number of oxygen vacancy in the obtained R-Mo-Ni Co₂O₄ is significantly increased by both Mo doping and Na BH₄ reduction.In addition,the doping of Mo can result in enhanced electrical conductivity and facilitated charge transfer.Finally,the R-Mo-Ni Co₂O₄ was used as electrode material in supercapacitors,which displays greatly improved supercapacitive performances such as higher specific capacity,rate capability and cyclic stability.