Preparation Of Functional Low-dimensional Graphene Materials For Energy Storage Devices

Graphene with planar conjugated structure presents many unique physical and chemical properties.Low dimensional graphene can be prepared as energy materials for energy storage and energy conversion.In this paper,functional low-dimensional graphene materials based on graphene has been designed and prepared,which showed excellent electrochemical and thermoelectric properties for energy storage and energy conversion fields.By structural regulation,Low dimensional graphene have been transformed from two-dimensional graphene to zero-dimensional graphene quantum dots and folding into quasi one-dimensional graphene nanobelts.From the perspective of functional regulation,heteroatom doping of graphene quantum dots and one dimensional graphene nanobelts have been fabricated,graphene fibers with high mechanical strength can be realized.In this paper,low-dimensional functional graphene materials in energy storage and energy conversion have been explored.The main research contents are as follows:a)Research of nitrogen-sulfur doped graphene quantum dots as metal-free electrocatalysts for enhancing electrochemical oxygen reductionA new zero-dimensional graphene quantum dot（N,S-GQDs）co-doped with nitrogen and sulfur co-doped was designed and synthesized.Using ammonia and sodium sulfide as the precursor,the N doping content in the prepared N,S-GQDs is as high as 9.36%.The support of N,S-GQDs on rGO was used as a metal-free electrocatalyst for the oxygen reduction reaction（ORR）in the alkaline system.The results showed that the electron transfer number was 3.82,which showed excellent electrocatalytic performance compared with that of Pt-C electrocatalyst.b)Research on Bi2Te3/GQDs nanostructures with size controllable GQDs as thermoelectric material for thermoelectric devicesSize controllable GQDs and Bi₂Te₃/GQDs hybrid nanostructures have been synthesized.Its thermoelectric performance showed a low thermal conductivity,and the power coefficient was significantly enhanced,which was related to the optimized Bi2Te3/GQDs interface thermoelectric transmission performance.In addition,the thermoelectric properties of Bi₂Te₃/GQDs hybrid nanostructures can be further enhanced by changing the size of GQDs,which can be attributed to optimizing the density and dispersion mode of GQDs in Bi₂Te₃matrix.At 425k,the maximum ZT of Bi₂Te₃/GQDs-20nm is 0.55.This work provides the insights for the structural design and synthesis of Bi₂Te₃-based hybrid thermoelectric materials,which will be important for future development of broadly functional material system.c)Research on quasi one-dimensional multilayer folded graphene structures in energy storage devices.Quasi-one-dimensional nitrogen-doped graphene nanoribbon（Quasi-1DNGNBs）was prepared by regulating the structure of graphene.The material was prepared as electrode material of supercapacitor,which has been showed a good structural stability,large surface area（718 m²/g）,internal resistance is low（0.5Ω）.The Quasi 1D NGNBs high specific capacity of 286 F/g at current density 1.0 A/g,and Quasi 1D NGNBs with unique morphology could be used as electrode material of new energy storage devices.d)preparation of high-strength one-dimensional graphene fibers by chemical modification and preparation of miniature energy storage devices.Graphene oxide fibers have been prepared by wet spinning using GO as precursor,ionic liquid and diamine as cross-linking agent between go layers.However,through annealing reduction at 2800 ^oC,the tensile strength of graphene fibers have got to 700 MPa,which presenting excellent mechanical properties.The micro-ultracapacitors prepared and showed good electrochemical performance,with the volume capacitance reaching 225 F/cm³,which showing high volume capacitance and good cycling stability.The initial results indicate that these fibers will be a good candidate to replace energy storage devices for miniaturized portable electronic applications.