The Synthesis And Electrochemical Properties Of Graphene/Polyaniline Based Composite Hydrogels

Supercapacitors become important energy storage device attributed to its fast charge and discharge,high power density and long cycle life.With the rapid development of wearable and portable electronics,flexible supercapacitor s have become the current research hotspot due to their excellent bending and folding properties and high specific capacitance.In engineering fields,to achieve the mechanical integrity of energy storage devices,it is also important and challenging to develop structural/stiff supercapacitors that present both high mechanical strength and excellent electrochemical performance.Electrode material is one of the key factors restricting the performance of supercapacitors.This dissertation mainly focuses on the structure design and fabrication of a variety of three-dimensional graphene/polyaniline（PANI）based composite hydrogels used as electrodes by different methods using conductive PANI with high pseudocapacitance contribution and graphene with excellent electrical conductivity and high mechanical strength as raw materials.In this dissertation,the molecular structure,formation mechanism,mechanical and electrochemical properties of composite hydrogels as flexible supercapacitors or structural/stiff supercapacitors have been investigated.The main research results of this dissertation are summarized briefly as follows:（1）Hydrothermal synthesis of PANI and graphene/PANI composite hydrogel（GPH7）.7 mg m L^-1 PANI dispersion and its mixture with 1 mg m L^-1 graphene oxide（GO）react hydrothermally at 180°C to form PANI hydrogel and GPH7.The synthesized nanopie-like PANI interconnect to form the three-dimensional network structure by self-crosslinking of PANI molecules.GPH7 presents interconnected network structure with graphene and PANI components.As-prepared PANI hydrogels and GPH7 assembled flexible supercapacitors show favorable specific capacitance(484 and 519.2 m F cm^-2,respectively),mechanical bending stability（capacitance retention～100%after 2000 cycles）and energy density(42.96 and 60.9μWh cm^-2,respectively).This work provides an approach to directly prepare PANI hydrogels using PANI dispersion.（2）Hydrothermal synthesis of m-phenylenediamine（m PD）functionalized graphene/PANI hydrogels（GMPH7）.1 mg m L^-1 m PD is introduced into the above GO and PANI systems to obtain the GMPH7 hydrogel by hydrothermal process at 180°C.GMPH7 possesses a sandwich layered crosslinked network structure with PANI chains intercalated between the graphene sheets.The introduced m PD weakens the interactions between GO and PANI,and protects the conjugated structure of PANI molecules,which endows GMPH7 with excellent electrochemical performance.The specific capacitance of GMPH7 reaches 514.3 F g^-1 at 1 A g^-1.The GMPH7 assembled flexible solid-state supercapacitors show high specific capacitance of 584.7 m F cm^-2at 1 m A cm^-2,108%capacitance retention after 2000 bending cycles and favorable energy density of 81.28μWh cm^-2.The GMPH7 supercapacitors with excellent electrochemical performance and flexibility are promising for the applications in flexible and wearable electronics.（3）The synthesis of functionalized graphene/PANI(DN-PGH/PANI_PA)stiff hydrogels based on double-crosslinked network design strategy.The DN-PGH/PANI_PAhydrogel is prepared by in-situ polymerization of aniline in a confined PGH hydrogel framework,which is obtained by hydrothermal process.A unique PANI morphology with a combination of nanodot protrusions and nanofibers is obtained,where nanodot protrusions are tightly anchored to graphene walls and nanofiber crosslinked graphene sheets to construct the double-crosslinked network.The DN-PGH/PANI_PA hydrogel is stiff and mechanically robust with a high tensile strength of 1.39 MPa at a small ruptured elongation of 0.42%.DN-PGH/PANI_PA hydrogels assembled symmetric supercapacitors achieve a superior areal specific capacitance of 3488.3 m F cm^-2,remarkable rate capability,excellent cycling stability（82.1%capacitance retention after 10000 cycles）,and notable energy density of 155μWh cm^-2.This double-crosslinked network design strategy establishes a promising approach to develop other stiff electrode materials as high performance structural/stiff supercapacitors.（4）The preparation of high-strength and multifunctional aramid nanofibers/reduced holey graphene oxide/PANI hydrogels（ANF/r HGO/PANI）by covalent crosslinking.The ANF/holey graphene oxide/PANI dispersion（ANF/HGO/PANI）undergoes the solvent exchange gelation and forms the hydrogels,which is subsequently treated by hydrothermal process at 120°C,thereby obtains the high-strength ANF/r HGO/PANI hydrogels.As-prepared ANF/r HGO/PANI hydrogels show high recoverability at high compressive strength of 13.8 k Pa.Moreover,ANF/r HGO/PANI aerogels possess high absorption capacity for oils（such as pump oil,kerosene and so on）with a range of24.5-44.0 g g^-1.ANF/r HGO/PANI films obtained after vacuum-drying exhibit a high tensile strength of 95.5 MPa.ANF/r HGO/PANI aerogel films assembled flexible supercapacitors deliver favorable electrochemical performance and durability even suffering bending and tensile force.In addition,ANF/r HGO/PANI thin films present good selective absorption of visible lights by controlling the doping level of PANI.As-prepared composite hydrogel based materials with such excellent performances are promising for applications in oil pollution removal,flexible loading-bearing energy storage devices and optical filters.（5）The preparation of graphene/ANF/PANI fiber（r GO/ANF/PANIF）composite aerogel based on the synergistic enhanced strategy of component and heat treatment.The r GO/ANF/PANIF composite hydrogels are prepared by 90°C reaction from GO and PANIF dispersions with introducing ANF.The r GO/ANF/PANIF composite aerogels with high mechanical strength are obtained after freeze-drying and subsequently heat treatment at 300°C.The composite aerogels exhibit good resilience and electrical conductivity.The assembled pressure sensors show low detection limit（40 Pa）,high sensitive sensing property(1.73 k Pa^-1),wide detection range（0.04-7.0k Pa）and excellent cycling stability.The assembled solid-state supercapacitors exhibit high specific capacitance(185.6 F g^-1)and good cycling stability（80%capacitance retention after 2000 cycles）.The composite aerogel with good sensing and electrochemical performances show the application prospects in the fields of electronic equipments including pressure sensors and supercapacitors.