The Synthesis And Electrochemical Performance Of Low Dimensional Molybdenum-based Oxides

With the impending exhaustion of fossil fuels and the increasing environmental pollution,low-cost and eco-friendly electrochemical energy storage devices capable of presenting high energy/power density and extended cyclability have been intensively studied.Compared with other electrochemical energy storage devices,supercapacitors and lithium-ion batteries are the most promising and widely used energy storage devices because of their unique advantages.Electrode materials have always been the core components of energy storage devices.The development of high-efficiency electrode materials has become more imperative to high performance electrochemical energy storage devices.As electrode materials,transition metal oxides have attracted increasing attention due to its higher specific capacity and energy density than carbon materials,and more safety than conductive polymers.However,the poor conductivity and severe volume expansion during charging and discharging always lead to poor rate performance and cycle stability.To futher address these problems,we choose metal molybdate and molybdenum trioxide as the research objects.The low dimensional nanostructured materials were successfully constructed by the component and structural design.The phase,structure and electrochemical performances of the nanostructured electrode materials were characterized and analyzed.The main results are summarized as follows:?1?A simple spray drying method with subsequent calcination in air was carried out to successfully introduce Co²⁺into NiMoO₄,and the Co_0.5Ni_0.5MoO₄ double-shelled hollow spheres?DSHSs?were finally obtained.The phase,morphology and structure were analyzed by XRD,Raman spectrum,TEM,XPS and so on.?2?As a cathode material for supercapacitors,the as-synthesized Co0.5Ni0.5MoO4DSHSs exhibit an improved pseudocapacitive property with specific capacitance of731 F g^-1 at 0.5 A g^-1.After 2000 cycles at 5 A g^-1,the capacitance retention can still reach 80%,while only 21%and 72%for NiMoO4 and CoMoO4 electrodes,respectively.Besides,the asymmetric supercapacitors were assembled with activated carbon materials as anode material,showing good electrochemical performance.Moreover,Co_0.5Ni_0.5MoO₄ also exhibits a high specific capacity(900 mAh g^-1 at 0.2 A g^-1 after 50cycles)and good cycle stability(756 mAh g^-1 at 1 A g^-1 after 1000 cycles).?3?MoO₃ nanowires were constructed by a simple and mild hydrothermal method.The phase,morphology and structure of MoO₃ nanowires were analyzed by XRD,SEM and TEM.As an anode material for supercapacitors,MoO₃ nanowires deliver a high specific capacity of 207 mAh g^-1 at 1 A g^-1 in acidic electrolyte(1 mol L^-1 H₂SO₄).The capacity retention is 74%after 100 cycles at 10 A g^-1.