The Preparation And Electrochemical Performence Of Transitionmetal Ni And Mo Based Electrode Composites

Worsening environmental problems and growing demand for energy motivate a rapid development of clean and renewable power sources as well as progressive electrochemical energy carriers.Supercapacitors?SCs?as a new generation environment-friendly electrochemical energy storage and conversion devices possess excellent power density,outstanding charging/discharging ability and near limitless lifespan,and have been drawn a dramatic interest in many application research areas,such as vehicle engineering,wearable electronics and aerospace.Metal oxide materials are well known as a significant category of supercapcitor electrode materials due to their amazing theoretical capacity,abundant faradic redox reactions and lesser costs.However,metal oxides are often associated with low conductivity and poor circulation stability.Among transition metal oxides,NiMoO₄ combines the advantages of both Ni and Mo elements and could realize a better specific capacitance.Nickel ions would provide high electrochemical activity and molybdenum ions can promot the conductivity of electrode materials in NiMoO₄.Furthermore,NiMoO₄ can not only increase the surface activity but also contribute to the stability of the structure by combining with carbon nanotubes or graphene.This thesis aimed to prepare and study structure,morphology and electrochemical properties of nickel-molybdenumoxide/carbonnanotubesandnickel-molybdenum oxide/reduction graphene oxide composites.In addition,the application of sodium-manganese oxide composites in supercapacitors is also studied.The content of this paper is as follows:?1?The porous C/NiMo O₄ composite was prepared by solution combustion method with nickel nitrate and ammonium molybdate as oxidant and citric acid as fuel.The effects of fuel-to-oxidant ratio on the morphology,composition and electrochemical performence of the combustion products were investigated.Furthermore,the CNTs/C/NiMoO₄ composites were obtained by adding an appreciable quantity of acid-treated CNTs into the optimized fuel-to-oxidant ratio precursor solution.The specific capacitance of the material has been improved sufficiently,and its specific capacitance reaches 1037 F g^-1at the current density of 1 A g^-1.The asymmetric supercapacitor?ASC?device was fabricated based on the CNTs/C/NiMoO₄ composites as anode electrode and the AC as cathode electrode,and the energy density of ASC is about 32.6Wh kg^-1 at power density of 150.5 W kg^-1.?2?NiMo O₄@rGO/NF composite was prepared by chemical precipitation and hydrothermal synthesis.The compound of each component?NiMoO₄,rGO and NF?contributes to the improvement of conductivity of electrode materials,and plays an active role in the electrochemical stability of electrode materials.Compared with Ni MoO₄ powder and NiMoO₄/NF,the prepared 3D NiMoO₄@rGO/NF composite delivers excellent specific capacitance of 1877 F g^-1 at charge/discharge current of 1 A g^-1.The as-made NiMoO₄@rGO/NF||AC ASC device exhibits a maximum energy density of 40 Wh kg^-1 at a power density of 218.2 W kg^-1.Moreover,the capacitance of the ASC reached 111.2%of the initial value after 8000 charging and discharging tests,which showed excellent electrochemical performance and structural stability.?3?The Na-Mn oxide composite was prepared by a simple molten salt method.The electrode metarials with different morphology and different components were synthesized by changing molten salt temperature.XRD,SEM,TEM,EDX,BET and electrochemical properties of each material were analyzed respectively.The Na-Mn-O 550 composite is considered as a composite material of Na_2-xMn₈O₁₆ and Na_0.7MnO₂,and its morphology is composed of nanorods and smaller nanoparticles.This composite exhibits a specific capacitance of 306 F g^-1 at 0.5 A g^-1.Na-Mn-O 550||AC ASC device possess the highest energy density of 20.0 Wh kg^-1 at a power density of 226.1 W kg^-1.In addition,the cycle retention rate of the device was 92.9%after 10000 charge and discharge process.These results show that the electrochemical stability of Na-Mn-O 550 composite material is prominent,and it has certain research and application potential.