Study On Electrochemical Supercapacitor Electrodes Based On Siloxene And Its Composites

Designing and developing renewable energy conversion and storage devices is an effective way to solve the current problems of fossil fuel depletion and environmental pollution.Electrochemical supercapacitors are considered as an advanced energy storage device due to their high power density and excellent cyclic stability,they fill the gap between ordinary capacitors and batteries.However,the low energy density still restricts their development.electrode materials can largely determine the performance of energy storage devices.Therefore,many researches focus on developing new electrode materials with unique structure and functional characteristics to obtain high-performance electrochemical supercapacitor energy storage devices.Due to its excellent electrical,mechanical and optical properties,atomic thickness and high specific surface area,two-dimensional(2D)materials have great potential for application in many fields such as optical,electrical and electronic devices,and have important research value.In the process of chemical reaction,the 2D material unique layered structure can provide a nanoscale reaction space and large specific surface area,and under certain conditions for the two-dimensional nanosheet surface has a large number of exposed surface atoms or functional groups,to provide more active site.These features make the 2D layered nanomaterials in the broad prospects for application of supercapacitor.In this paper,new two-dimensional materials are mainly taken as research objects,siloxene and siloxene/reduced graphene oxide composite hydrogels(SGH)nano-electrode materials are designed and synthesized,and their physical and chemical properties and supercapacitor properties are investigated.The specific work is as follows:(1)A new two-dimensional layered material siloxene was prepared by topological transformation with layered calcium silicate as the precursor,and its supercapacitor performance were investigated.Firstly,the layered calcium silicate was etched and stripped by concentrated hydrochloric acid to achieve topological transformation.Finally,siloxene two-dimensional layered structure materials are obtained.Scanning electron microscope,transmission electron microscope,automatic microporous physical adsorption analyzer,infrared spectrometer,X-ray diffractometer,Raman spectrometer and X-ray photoelectron spectrometer were used to study its morphology,structure and physical and chemical properties.Then,in a three-electrode system,the electrochemical performance of 2D siloxene was tested by cyclic voltammetry,electrochemical impedance spectroscopy,constant current charge and discharge,and cyclic stability tests in 1 M H2SO4 acid electrolyte.The results showed that 2D siloxene had layered structure and mesoporous structure,abundant oxygen-containing functional groups(-OH)on the surface,and high specific surface area(113.9 m2 g-1).At the current density of 1 A g-1,siloxene electrode material has the specific capacitance of 23 F g-1.In addition,the two-dimensional layered structure of siloxene has excellent long-term cycling stability(at the current density of 2 A g-1,the capacitance retention rate after 10,000 cycles is 94.5%).(2)An oxygen-rich siloxene/reduced graphene oxide composite hydrogels(SGH)was prepared by hydrothermal synthesis method with graphene oxide(GO)and siloxene as the precursor,and the supercapacitor performance of the composite was investigated.Firstly,siloxene/reduced graphene oxide composite hydrogels with three-dimensional hierarchical structure and abundant oxygen-rich functional groups were obtained by one-step hydrothermal reaction with GO and siloxene as raw materials.Scanning electron microscope,transmission electron microscope,automatic microporous physical adsorption analyzer,infrared spectrometer,contact angle measuring instrument,X-ray diffractometer,Raman spectrometer and X-ray photoelectron spectrometer were used to study its morphology,structure and physical and chemical properties.Then,in a three-electrode and two-electrode system,the electrochemical performance of SGH was tested by cyclic voltammetry,electrochemical impedance spectroscopy,constant current charge-discharge and cyclic stability tests in 1 M H2SO4 acid electrolyte.The results showed that GO was reduced after a one-step hydrothermal reaction,and a small amount of siloxene nanosheet were inserted between the reduced graphene oxide flakes.Siloxene was used as a“spacer”to form a three dimensional structure with graphene,which improved the specific surface area of the material.Importantly,the surface chemistry of graphene sheets has been changed by siloxene,introducing additional oxygen-containing functional groups,whose abundance contributes to the formation of pseudcapacitors and to the improvement of material wettability.The specific capacitance of SGH is 520 F g-1 at the current density of 1 A g-1,and the capacitance value of 76.9%can be maintained even if the discharge current density is increased to 100 A g-1.In addition,at a high current density of 50 A g-1,the capacitance value of SGH maintained 96.3%of the initial capacitance value after 15,000 cycles,showing its excellent cyclic stability.Finally,the symmetrical supercapacitor assembled by SGH//SGH has outstanding performance with a high energy density of 24.5 Wh kg-1 at a power density of 399.6 W kg-1.Therefore,siloxene/reduced graphene oxide composite hydrogels is a promising electrode material for high-performance supercapacitors.