Fabrication And Electrochemical Properties Of Ni-Co Based S/O Compounds Grown On Conductive Carbon Cloth

In recent years,with the rapid development of science and technology,the updated iteration of brilliant hardware products has been accelerating.The smart wearable devices have become more and more popular.However,the upgraded wearable devices are still in demand because of their important energy storage platform.Compared with the traditional energy storage platforms such as lithium-ion batteries and fuel cell,due to its inherently fast in charge and discharge,easy to use and prepare,high power density,environmental friendliness and good cycle stability,Supercapacitors have attracted the attention of more and more researchers.At the same time,flexible supercapacitors have very good flexibility and mechanical properties in addition to the advantages of conventional supercapacitors.Therefore,flexible supercapacitors have great potential as energy storage devices for smart wearable devices.On the basis of above analysis,this thesis focuses on the preparation of flexible supercapacitor electrode materials based on conductive carbon cloth and simplely assembles into flexible supercapacitor devices.The energy storage mechanism is explored by the composition and structure of the electrode materials.Moreover,the electrochemical performance of assembled flexible supercapacitor devices was also analyzed and discussed,and the following four aspects were studied:(1)The commercial conductive carbon cloth was used as a flexible current collector.The NiMoO4/CoMoO4 nanorod arrays structure was grown on the surface of the conductive carbon cloth fiber(NCMO@CC)by a simple one-step hydrothermal growth and high-temperature annealing method.Then,Ni-Co-S nanosheet structure was electrochemically deposited on the periphery of NiMoO4/CoMoO4 nanorod arrays,and Ni-Co-S@NiMoO4/CoMoO4 nanorod arrays composite grown on conductive carbon cloth(NCMOS@CC)was obtained as the positive material of a flexible supercapacitor.The morphology,composition,and structure of the prepared electrode materials were analyzed by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffractometry(XRD)and X-ray photoelectron spectroscopy(XPS).The results show that the obtained electrode material has a morphology similar to that of the core-shell structure and good crystallinity.The electrochemical performance tested in a 1 mol L-1 of KOH electrolyte shows that the mass-specific capacitance of the prepared NCMOS@CC can reach 778.1 F g-1 at the current density of 0.5 A g-1 and when the current density increased to 4 A g-1,the mass-specific capacitance can still reach 648.4 F g-1.(2)Two different flexible anode materials were prepared,including conductive carbon cloth loaded with Bi2O3 nanosheet(Bi2O3@CC)and activated carbon coated conductive carbon cloth(AC@CC).Firstly,the morphology of two different anode materials was characterized by SEM.The results show that the Bi2O3 crystal grows in the form of nano-sheets on the periphery of the conductive carbon cloth fibers,and the activated carbon powder exhibits a loose porous structure.Secondly,the electrochemical properties of the two negative electrodes were tested separately,and the proton conservation equation was used as the assembly criterion.The two negative electrodes and the NCMOS@CC positive electrode were assembled into two flexible layers with 1 mol L-1 KOH solution as the electrolyte respectively.They were assembled into two different types of flexible supercapacitor devices,namely battery type capacitors and capacitor type capacitors.Their respective electrochemical properties were analyzed and tested.The results show that NCMOS@CC//AC@CC exhibits a capacitance-like behavior with a mass specific capacitance of 93.3 F g-1 at a current density of 0.25 A g-1.NCMOS@CC//Bi2O3@CC exhibits a battery-like behavior with a mass specific capacitance of 45.3 F g-1 at a current density of 0.25 A g-1.For the cyclic stability tested at the high current density of 3 A g-1,both flexible supercapacitors showed very good cycle stability,and after 5,000 cycles,the capacitance retention rate was above 98%.(3)Firstly,a hollow Co8S9 nanoneedle(Co8S9-0@CC)was prepared by a two-step hydrothermal method on the surface of conductive carbon cloth fibers.Secondly,sodium hypophosphite was used as a phosphorus source in a chemical vapor deposition furnace for annealing and phosphating to obtain a phosphorus-doped Co8S9 nanoneedle(P-Co8S9@CC).Finally,Ni(OH)2 nanosheets were electrochemically deposited on the surface of P-Co8S9@CC by electrochemical workstation with constant voltage mode using nickel nitrate aqueous solution as nickel source to obtain(P-Co8S9/Ni(OH)2@CC).The SEM was used to observe the micromorphology of the samples at each stage.The prepared samples were well-formed and evenly distributed.It was observed by TEM that the Co8S9 nanoneedle has a very good hollow structure.At the same time,the P-Co8S9/Ni(OH)2@CC sample has a hollow structure inside,and the periphery is covered with Ni(OH)2 nanosheets,and the structure is uniform.The crystal structure of the sample and the valence and bonding mode of each element were characterized by XRD and XPS.The electrochemical performance of the three samples was tested by electrochemical workstation using 3 mol L-1 KOH solution as the electrolyte.The results show that P-Co8S9/Ni(OH)2@CC has better electrochemical performance than others under the same conditions where the mass-specific capacitance can reach 519.5 F g-1 when the current density is 0.5 A g-1 while the P-Co8S9@CC is second,and Co8S9-0@CC is the worst.However,the rate performance of P-Co8S9/Ni(OH)2@CC is little worse than the others.(4)Using soybean dregs as a precursor,a nitrogen-doped porous carbon powder was obtained by adding a pore former potassium acetate and urea as a nitrogen source.SEM,TEM and N2 adsorption-desorption isotherm test(BET)results show that the material mainly contains micropores and a small number of mesopores.A small number of heteroatoms were detected in the material by an organic element analyzer.The electrochemical performance test showed that in the same case,the specific capacitance of the potassium acetate and soybean dregs 2:1 and the urea-doped sample(PC-4)was the largest,and the mass-specific capacitance at a current density of 0.5 A g-1 can reach 175.8 F g-1.The electrode was assembled into a flexible supercapacitor device with a P-Co8S9/Ni(OH)2@CC positive electrode of the previous chapter and a 3 mol L-1 KOH solution as an electrolyte to evaluate its electrochemical performance.The results show that the mass-specific capacitance can reach 67.9 F g-1 at the current density of 0.25 A g-1.The cyclic stability of the device was tested at the high current density of 4 A g-1 and the capacitance retention rate was 74.21%after 5000 cycles.