The Fabrication Of Carbon-based Composites And Their Applaction In Supercapacitors

Supercapacitor is a promising way to provide energy for the sustainable energy storage device and convenient electronic equipment supply.The improvement of the charge ability and the rate capability,the decrease of the production cost to achieve large-scale use,are the challenges.In this paper,three-dimensional porous network structure of carbon-based composite electrodes were employed to overcome the above problems,including the improved construction method of electrode materials,crystal orientation principle of inorganic materials,the observation of charge and discharge behavior by non-in-situ characterization methods,in-depth analysis of the kinetics of electrode,the mechanistic insight into the nanoarchitecture-charge storage-kinetics correlation.With the special goal to solve the above problems,this paper designed four kinds of three dimensional networks.The structure of the carbon matrix composites are listed as follows:?1?Cellulose tailored anatase TiO₂ nanospindles in three-dimensional graphene composites for high-performance supercapacitorsIn recent years,many researchers interested in producing high performance from bio-based 3D carbon nanomaterials,which is low cost,easy to obtain,and no harm to human beings.Renewable natural polymer cellulose is the main organic plant,with three levels of hierarchical structure,is an ideal platform for the design of three-dimensional carbon materials.In this paper,we use the natural polymer cellulose,as an induced agent for the anatase crystal with high-energy surface exposed,and a shielding agent for the surface oxygen functional group,to tailor the inorganic anatase TiO₂/rGO nanospindles with high energy surface {010} exposed.Because the synthesis of cellulose rich hydroxyl,preferentially adsorb on anatase?001?surface and form the Ti complexes.As a result,the anatase grow along the[001]with the {010} faces exposed.At the same time,the monodisperse anatase nanocrystals can be formed,because the large viscosity of the cellulose hydrogel can reduced the release rate of the Ti containing species.The paper reported a new and scalable strategy for the in situ preparation of anatase TiO₂ nanospindles in the three-dimensional RGO structure?3D TiO₂/RGO?using cellulose as a structure-directing agent to control the growth of the TiO₂ crystals.In this strategy,compared with previously reported methodologies,the use of cellulose allows the simultaneous growth of the TiO₂ nanospindles and the formation of the 3D RGO structures.TEM and XRD data indicated that the spindle shape of the TiO₂ crystals is formed through the preferential growth along the[001]direction,whereas growth in the[010]direction is restricted by the adsorption of cellulose.Through this growth mechanism,the TiO₂ crystals form a spindle shape with the {010} facets preserved.Because of the 3D RGO structure,spindle-shaped TiO₂ crystals,and preserved highenergy {010} facets,our 3D TiO₂@RGO?Ce 1.7?composite exhibits significantly improved performance as an electrode material for supercapacitors.In particular,this material has a high specific capacitance?ca.397 F g-1?,a high energy density?55.7 Wh kg-1?,and a high power density?1327 W kg-1?relative to the masses of RGO and TiO₂.?Chapter 2??2?Porous nitrogen-rich carbon materials from carbon self-repairing g-C₃N₄ assembled with graphene for high-performance supercapacitor.Nitrogen-doping is one of the keys to improve the performance of carbon-based supercapacitor.But there are some problems in conventional preparation methods,such as the uneven distribution of nitrogen atoms in the carbon matrix obtained by pyrolysis of nitrogen-containing carbon materials,and the porous structure is easy to collapse in the heat treatment.In this paper,we designed a facile strategy for the construction of a monolith of porous nitrogen-rich carbon via solution selfassembly of carbon-repairing g-C₃N₄ and GO colloidal solution.Carbon source from ethanol was in situ introduced into g-C₃N₄ during the polymerization of melamine?MA?in solvothermal process by hydrogen bond.The possible detailed reaction pathway for the development of C-C₃N₄ was shown in.Then,GO sheets were introduced into C-C₃N₄ to form porous frameworks through cross-linking interactions,such as ?-? interaction and hydrogen-bonding interaction.During the hydrothermal process,GO was transformed into rGO to get C-C₃N₄@rGO hybrid.The C-C₃N₄@rGO was fabricated as the supercapacitor electrode,which inherited the structural characteristics of the porous nitrogen-rich carbons with enhanced electrical conductivity and exhibited faradaic pseudocapacitance behavior.The faradaic pseudocapacitance active sites were firstly proven to be oxygencontaining groups and the carbon atoms close to nitrogen atoms.This has been proposed by several research groups but there exists a lack of experimental evidence.?Chapter 3??3?Nearly vertical polyaniline/reduced graphene oxide nanosheets on TiO₂ nanotube arrays as a high-performance supercapacitor electrode:understanding the origin of high rate capability.In addition to endurance,the energy storage device also needs fast charging and discharging,and the rate capability is an important parameter to describe the fast charge and discharge.In general,the factors affecting the rate performance are conductivity,ion diffusion,and the specific surface area of the electrode material.Pseudocapacitance involving ion intercalation into pseudocapacitive materials for redox reactions or doping/dedoping process in conductive polymers,often suffers from a quite slow kinetics,which seriously hinders the rate capability of supercapacitors.Keeping high surface capacitance contribution is proposed to address this issue.Here,a porous scaffold,TiO₂ nanotube arrays grown in a Ti foil?TiO₂/Ti?is selected as the current collector for electrodeposition of porous polyaniline/reduced graphene oxide?PANI/rGO?hybrid film.The PANI/rGO@TiO₂/Ti was quantitatively evaluated to possess surface capacitance contribution up to 58%at high rates?>25 mV s-1?and large electron transfer coefficient of 2.Due to the benefits,the electrode not only shows an ultrahigh gravimetric capacitance of 908 F g-1 at 1 mV s-1,close to the theoretical gravimetric capacitance?about 964 F g-1?for PANI-based pseudocapacitors,but also delivers an outstanding rate capacity of 310 F g-1 at 500 mV s-1.PANI/rGO@TiO₂/Ti also shows excellent cycling stability with capacitance retention of 80%after 10000 cycles at a high current density of 25 A g-1.?Chapter 4??4?Achieving high pseudocapacitance of MXene by electrochemical cation intercalation and surface modification.Inspired by the excellent performance of graphene in the energy storage field,other emerging two-dimensional materials,such as g-C₃N₄ and MXenes,have also gradually affected the new generation of clean,efficient and renewable energy systems.2D graphene analogues layered materials have similar structure with graphene,such as the planar topological structure,and the thickness of the thin?only a few or even an atomic layer thickness?.The composites of heterostructure interface of carbon and emerging 2D material can be prepared based on the similar crystal surface and the interaction of Van der Waals.Traditional delamination of two-dimensional layered material must use strong acid and base during the fragment splintering process.It is necessary to develop a rapid and simple delamination method.This paper fist use cation electrochemical delamination method to obtain delaminated two-dimensional layered material with large number of oxygen terminal from the corresponding bulk.This is a universal delamination method for the two-dimensional layered material,such as TiN.?Chapter 5?...