Capacitive Properties Of GC₃N₄/graphene-based Transition Bimetallic Sulfides

With the non-renewability of fossil fuels and the greater demand for energy from production development,the continuous deterioration of environmental and ecological problems have promoted the exploration and research of new energy storage equipment and materials.As an emerging green energy storage element,supercapacitors have energy storage performance between traditional capacitors and batteries,with good power density and energy density,long cycle life,rapid charge and discharge,wide operating temperature range of-40?+70?,able to adapt to most extreme working environments.Therefore,it is the key research direction for future green,friendly and sustainable development.Energy density and power density are important parameters for the evaluation of device performance,and are also important factors that limit the development of supercapacitor materials.The development and research of electrode materials with high energy density or the improvement of the structure of existing materials are the main methods of current research.As a prominent representative of carbon materials,graphene is widely used in the field of supercapacitors.Transition metal disulfides have high theoretical specific capacitance and adjustable interlayer spacing,a two-dimensional layered structure similar to graphene.The edges are in a high-energy state due to the absence of atoms and have high chemical activity.Graphene-like carbon nitride(g-C₃N₄)is a two-dimensional layered structure material with a nitrogen content of up to 60%.It has a relatively stable physical and chemical structure,and the raw materials are cheap and easy to obtain and environmentally friendly.In this thesis,the g-C₃N₄/graphene-based transition bimetallic sulfide composite material was synthesized by a one-step hydrothermal method,using scanning electron microscope(SEM),X-ray diffraction analysis(XRD),X-ray photoelectron spectroscopy(XPS)and other methods for characterization of the component,and the samples were electrochemically tested by cyclic voltammetry(CV),galvanostatic charge-discharge(GCD),electrochemical impedance spectroscopy(EIS)and other methods.The work of this paper mainly includes:(1)One-step hydrothermal synthesis of Mo S₂/NPRGO/C₃N₄ composite materials to explore the best ratio of carbon nitride to graphene.Under the three-electrode system,the current density reached 663 F g^-1 when the current density was 0.5 A g^-1,and it was assembled into a device.When the power density of the symmetrical supercapacitor device was 375 W kg^-1,the energy density was 18.75 Wh kg^-1,when the power density is 7484 W kg^-1,the energy density can still reach 4.16 Wh kg^-1.When the current density is 3 A g^-1,the capacitance retention rate still reaches 94.4%after 5000 cycles.(2)One-step hydrothermal synthesis of WS₂/Mo S₂/NPRGO/C₃N₄ composite materials to explore the optimal molar ratio of molybdenum source to tungsten source.In the three-electrode system,the current density reaches 410 F g^-1 at 0.5 A g^-1.When the power density is 400 W kg^-1,the energy density is 31.33 Wh kg^-1.When the power density is 8000 W kg^-1,the energy density can still reach 6.66 Wh kg^-1.Due to the synergy between the composite materials,WS₂/Mo S₂/NPRGO/C₃N₄ exhibited excellent cycle stability,cycling 9000 cycles at a current density of 4 A g^-1,the capacitance value still did not attenuate.