Synthesis Of Transition Metal Sulfide/Selenide For Electrochemistry Applications

With the continuous development of human society and economy,the demand for energy consumption is rapidly increasing.Therefore,generating and storing clean and efficient energy sources as the alternatives to the fossil fuels are crucial to maintain the sustainable development of society and economy.In the field of the energy production,hydrogen,as one of the most promising clean energy resources,can be generated during the water splitting through the hydrogen evolution reaction(HER)during which catalysts are often needed to improve the reaction efficiency.At present,the most efficient heterogeneous catalysts for HER are based on platinum,while which is expensive and rare.So,it is imperative to find novel,high-efficiency and low-cost catalyst materials to replace the commonly used platinum-based electrodes.On the other hand,in the regime of energy storage.Due to limited lithium resources,commercial lithium ion batteries(LIBs)are difficult to continue to meet the demand of business issues.Sodium ion batteries(SIBs)because of their advantages of low cost,high safety,have been considered to be the most promising alternative of LIBs and received a lot of attention over the past few decades.However,due to the large ion radius and molar mass of sodium ions,it is difficult to insertion/extraction sodium ions in conventional electrode materials,so that it is particularly important to explore and design excellent electrode materials to improve the performance of SIBs.With considering the above mentioned challenges in maintaining efficient HER process and achieving high capacities in SIBs,In this thesis,the transition metal sulfides/selenides(MXs)have been systematic investigated and demonstrated as the alternative low-cost electrode materials for HER and SIBs.This work has been done with the following main contents:1.The fabrication of MoS2/Ti/Si micro-rods(MRs)as efficient anodes in HER.Firstly,3D Ti/Si MRs were produced by the template method accompanied with inductively coupled plasma(ICP)etching and magnetron sputtering deposition.Then,with low cost,high efficiency and good stability,MoS2 nanoflowers have been synthesized on Ti/Si MRs as a freestanding working electrode in HER through a hydrothermal process.Compared with pure MoS2 catalyst,the MoS2/Ti/Si MRs composite structure presents larger specific surface area,faster electronic transferring characteristic,and more catalytically active sites.Therefore,the high catalytic activity with a low over-potential of 219 mV at 10 mA cm-2 and Tafel slope of 56 mV dec-1 were accomplished during the HER process.2.The synthesis of cobalt-molybdenum binary transition metal selenide as efficient anodes in SIBs.Firstly,the precursor CoMoO4 was synthesized on the carbon cloth by hydrothermal method to obtain the composite material(so called CoMoO4@C).Then 3D CoMoSe4 nanosheets have been synthesized coating on the network fibers of the carbon cloth(so called CoMoSe4@C)as the anode in SIBs by the plasma-assisted selenization process.Due to the high specific surface area from the well-defined 3D structure,high electron conductivity and bi-metal electrochemical activity,superior SIBs performances with a large reversi’ble capacity of 475 mA h g-1 at 0.1 A g-1 in the voltage window of 0.5 to 3 V,and after 50 cycles,the capacity retention rate can still exceed 80%.At the same time,this simple synthesis method can be widely used in the preparation of other bimetallic sulfide compounds,and has a broad application prospect in the fields of energy storage and energy conversion.In summary,this thesis successfully prepared a composite structure of MoS2 nanoflowers coated on 3D silicon-based micro arrays,and verified its high efficiency in hydrogen evolution reaction.In addition,a new synthesis method for preparing cobalt-molybdenum binary transition metal selenide was developed and its high-efficiency sodium storage characteristics were studied.This work provides an important theoretical and experimental basis for the further development of transition metal selenium/sulfide in energy storage/producing systems.