Preparation And Properties Of Self-supporting Electrodes Based On Carbon/MOFs Derivatives For Hybrid Supercapacitor

Nowadays,rigorous environmental matters and people’s individual needs continuously motivate substantial investigate for smart electronic products.Among them,supercapacitors exhibit many superior properties,such as long life,extremely fast charge/discharge capabilities,and ideal power density,making it as a potential device for energy storage technology.Unfortunately,the large-scale development of supercapacitors has been mainly obstructed by their low energy density.The key to solving the above problems is to improve the capacity and potential voltage of the electrode material.Great efforts still needed to explore different kinds of ideal electrode materials for supercapacitor.Recently,the self-supporting film with high performance and no additives,have tremendous application prospects as electrode materials in the development of small devices,due to their remarkable composite structures.How to construct such remarkable film is the focus of our research.Metal-organic framework（MOF）is a fresh type of material that combines rich porosity,large specific surface area,easy-to-adjust components,controllable structure,and easy synthesis.Especially,MOF-derived materials have been considered as most prospective materials for efficient supercapacitors.However,it is not satisfactory that most of them are powder,as well as its relatively poor conductivity and cycle life,which greatly limit its large-scale development.At present,flexible carbon materials,represented by carbon nanotubes and graphene,have caused great concern to prepare flexible films,due to their excellent thermal/mechanical stability,ideal conductivity and unique flexibility,wide source,low-cost and pollution-free.However,the main disadvantage is that the relatively poor capacity limits their further development.One feasible means that may allow the above shortcomings to be relieved is the combination of high capacity active materials to improve the overall electrochemical performance.Therefore,the main idea of this paper is introducing MOFs derivatives into carbon materials by self-assembly method to prepare multiple composite films with unique structures.Not only can fill the insufficient of them,but also can achieve better electrochemical performance through the synergistic effect and complementary advantages of them.The primary content and conclusions are as follows:1.First,Cu（OH）₂ nanowires and carbon nanotubes are mixed uniformly and assembled into a composite film by vacuum filtration.Then a simple chemical immersion method and hydrothermal vulcanization method are used to prepare a unique structure CCS composite film.This unique film can make the porous CuS polyhedron directly penetrate the carbon nanotube film without any additives to form a self-supporting flexible film.After decorating with CuS,CCS film can deliver a specific capacitance of 606.7 F/g.The assembled asymmetric supercapacitor,constitute with CCS film and CNC film,can achieve a outstanding energy density of38.4 W h/kg at 750 W/kg power density.In addition,after 6000 cycles,the capacity retention rate can reach up to 87.0%.It can be seen that the unique CCS thin film obtained superior electrochemical performance after self-assembly.2.In order to explore simpler method to prepare a film with better performance.The carbon nanotubes are interwoven into a network structure through the self-assembly method and used as a substrate,which not only can provide rich migration path for ions,but also can effectively improve the overall conductivity of the film.The loaded NiCo-LDH with large specific surface area and varied oxidation state,provide a large number of active sites and make a great pseudocapacitor contribution to the film.After decorating NiCo-LDH nanosheets with higher capacitance,the specific capacitance can achieve 1213.7 F/g at 1A/g.In addition,the fabricated asymmetric supercapacitor,constitute with CNT@NiCo-LDH film and CNT@NC film,can deliver up to a outstanding energy density of 37.4 Wh/kg at 750 W/kg power density,as well as show a preeminent cycle life,retaining 94.5%of the primal capacitance after 5000 cycles.It can be seen that we have further realized the preparation of flexible unique films with higher capacitance.3.To gain more insights into the universality of the above self-assembling composite film method.Free-standing graphene and hollow carbon spheres（NC）and Co（OH）₂,were mixed uniformly to fabricate a unique film（graphene@NC@ZIF-67-derived Co₉S₈）by vacuum filtration.In addition,the in-suit growth ZIF-67-derived Co₉S₈ not only can effectively enhance the capacitance of the composite film,but also can avoid the problem of Co₉S₈ particle accumulation.Graphene@hollow carbon spheres@Co₉S₈ films can acheive a gravimetric and volumetric capacitance of 540 F/g and 842.4 F/cm³ respectively.The prepared asymmetric supercapacitor,constitute with graphene@hollow carbon sphere@Co9S8 film and graphene@hollow carbon sphere film,can reach up to gravimetric energy densities of 23.6 Wh/kg and volumetric energy densities of 28.7 W h/L,respectively,as well as show long cycle life after 8000 cycles.It also shows that the self-assembly method of the composite film has universality and provides reference value for self-assembly film.