Research On Regulation Of Structures Of Free-standing Carbon Based Films And Their Functional Applications

Nowadays,functional carbonaceous materials are one of the hottest research topics,due to their easy preparation methods,low cost and unique characteristics.They also have some outstanding performances,such as good mechanical properties,excellent electrical conductivity,superhydrophobic/superhydrophilicity properties,and outstanding electrochemical properties.These unique properties can endow them with abilities to meet different demands,which lead them to become the research topic in the field of materials science and technology.With the development of industry and technology,high-performance functional carbonaceous films are required to meet the applications in different areas,including X-ray mask plate,field effect transistor devices(FET),gas sensors,lithium ion batteries,supercapacitors,light catalysis fields,sewage treatment and seawater desalination,biological applications,and so on.Therefore,it is of great significance to study and explore the basis and theory of high performance carbonaceous films,which is important and meaningful to develop continuous exploration and application of high-performance functional carbonaceous films.In general,the structure determines the final properties of the materials.Therefore,it is meaningful to develop and optimize functional carbonaceous films from the perspective of structural design and regulation of carbonaceous films to realize high-performance functional films.This work focuses on the surface/interface of functional carbonaceous films,and studies the characteristics of surface/interface of carbonaceous films and their micro/nano structure regulation,in order to reveal the relationship between their structures and performances;and establish high-performance structure models to clarify their mechanisms,so as to establish theoretical basis for the preparation of high performance carbonaceous films,which is very important and meaningful to realize the high-performance applications of carbonaceous films.Detailed research highlights are as follows:1.Research on three-dimensional networks with seamless interface in-situ reinforced structure for mechanical enhancement of glassy carbon(GC)matrix.Multi-walled carbon nanotubes(MWNT)were uniformly dispersed in polyimide matrix(GC precursor)at first by in-situ polymerization.Then,MWNT-reinforced PI films were treated by high temperature carbonization.Finally,MWNT networks with seamless interface enhanced MWNT/GC composite films were obtained.The mechanical properties of the MWNT/GC composite films were improved by the construction of the seamless interface of the carbon nanotubes in the matrix through the modification of the MWNTs,in-situ polymerization combined with high-temperature carbonization.The experimental results showed that the 5 wt.%MWNT/GC composite films have the highest three-point bending strength(575.5MPa)and the corresponding three-point bending modulus(7.7 GPa)respectively,increased by 54%and 78%respectively when compared with pure GC membrane.It is meaningful for the preparation of free-standing carbonaceous films based on the homogeneous one-dimensional carbon nanotubes network and surface modification processes to achieve seamless interface of three-dimensional network structure design and construction.The obtained composite carbon films have great potentials in the X-ray mask application fields.2.Research on the hierarchical structure of graphene reinforced glassy carbon films and their mechanical properties and superhydrophobic properties.Free-standing graphene reinforced graphene/GC composite films were prepared by simple methods through in-situ polymerization(graphene was uniformly dispersed in polyimide matrix),and high temperature carbonization which formed barrier effect and promoted uniform growth of carbon nanoarrays on the surfaces.Therefore,hierarchical structures with nanoarrys on surfaces of graphene reinforced glassy carbon films were successfully constructed.Such hierarchical structure shows fabulous rigid structure and mechanical properties.Mechanical results showed that when the content of graphene was 0.5 wt.%,rGO/GC composite films had the highest three-point bending strength of 202.6 MPa and modulus of 33.8 GPa,increased by 99%and 99%respectively when compared with pure GC membrane.Moreover,the hierarchicalstructureshowedsuperhydrophobicpropertiesafter1H,1H,2H,2H-Perfluorodecyltrichlorosilane interface treatment.The hierarchical structure is very meaningful for the design of superhydrophobic properties and rigid structures of carbonaceous films.3.Research on the design of three-dimensional graphene-based porous film electrode materials by steamed water regulation and their electrochemical performance.The regulation and optimization of the structural of graphene films is essential to achieve high gravimetric specific capacitance and high volumetric capacitance.In this work,we put forward steamed water controllable regulation technology to obtain three-dimensional graphene-based porous films under moderately high temperature and high pressure.Steamed water regulation technique was applied to regulate high-concentration GO sols under high pressure and high temperature in closed vessels,and the resultant free-standing flexible rGO films exhibited favorable mechanical robustness as well as excellently controllable areal and volumetric capacitances(with a highest gravimetric specific capacitance,a highest areal specific capacitance,and a highest volumetric capacitance up to 340 F/g(1A/g),915 mF/cm~2(1 mA/cm~2),and 326 F/cm~3(1 A/cm~3),respectively),revealing the versatile behavior of this regulation technique for high-performance flexible energy storage.In addition,a typical assembled all-solid-state supercapacitor based on as-fabricated graphene films shows large gravimetric and areal specific capacitances.Therefore,the steamed water regulation on preparation of graphene films is very meaningful to prepare high-performance graphene film electrodes,which highlights its great potential for high-performance flexible energy storage devices.4.Research on the preparation of three-dimensional graphene based composite films by steamed water controllable regulation and their electrochemical performance.In this work,we put forward a novel method to prepare three-dimensional graphene based composite films by steamed water controllable regulation under moderately high temperature and high pressure.The experimental results showed that the PANI nanofibers were perfectly embedded in graphene network structure formed in the novel three-dimensional layered structure.The intimate incorporation of PANI nanofibers in rGO sheet skeletons not only favored rapid electron and ion transport,but also exhibited excellent electrochemical behavior.The obtained rGO/PANI(50%)hybrid film exhibited a highest gravimetric specific capacitance of 1182 F/g at 1 A/g in the three-electrode test.The assembled symmetric device showed both a high capacitance of 808 F/g at 1A/g and high gravimetric energy density(28.06 Wh/kg at a power density of 0.25 kW/kg).The novel 3D structure constructed by steamed water regulation techniques pave a new avenue for other graphene hybrid networks fabrication and holds a great potential for high-performance energy storages.5.Research on the design of three-dimensional rGO-PANI hybrid films and their electrochemical performances.High performance flexible electrode materials were fabricated by in-situ electrostatic self-assembly technique.The obtained composite films had the excellent hierarchical three-dimensional porous structures,with PANI fibers wrapped by graphene network.Supercapacitors were assembled based on those flexible rGO-PANI hybrid films.Since PANI nanofibers(NFs)were tightly wrapped by rGO nanosheets and subsequently embedded inside rGO nanosheet network skeletons,so the intimate incorporation of PANI NFs in rGO sheet skeletons and the direct interconnection of all rGO nanosheets in the hybrid electrodes enabled rapid electron and ion transport as well as excellent electrochemical behavior.The as-fabricated film electrodes with this unique structure showed a highest gravimetric specific capacitance of 921 F/g and volumetric capacitance of 391 F/cm~3.The assembled solid-state SCs gave a high specific capacitance of 211 F/g(1 A/g),a high area capacitance of 0.9 F/cm~2,and a competitive volumetric capacitance of 25.6F/cm~3.The SCs also exhibited outstanding rate capability(~75%retention at 20 A/g)as well as excellent cycling stability(100%retention at 10 A/g for 2000 cycles).Additionally,no structural failure and loss of performance were observed under the bending state.In conclusion,the ideal conductive network structure of the obtained rGO-PANI hybrid films not only avoided the stacking of rGO nanosheets,but also ensured that all rGO nanosheets are connected to each other effectively,which utilized the double-layer capacitance characteristics of the rGO nanosheets and the pseudopolecular properties of the PANI fibers,resulting in a high specific capacitance of the thin film electrode material.This structure design paved a new avenue for engineering rGO/PANI or other similar hybrids for high performance flexible energy storage devices.