Preparation Of Graphene Fibers And Its Application In Supercapacitor And Sensor

As the firstly discovered two-dimensional atomic crystal,graphene not only has the excellent electrical,optical,mechanical and thermal properties,but also has promising applications in energy storages,sensors,flexible displays and carbon-based materials.Recently,how to design,construct and transform the excellent properties of graphene nanosheets into multifunctional graphene-based macromaterials has attracted many researchers' attentions.As an important graphene-based macro-material,graphene fibers have promising applications in energy storage and sensors.Aiming at the complicated preparation of graphene fibers and their poor performances at present,we chose graphite as raw material to prepare graphene oxide and then used graphene oxide solution to fabricate graphene fibers.In this work,flexible and high-strength graphene fibers were fabricated by wet spinning and dry spinning methods.Graphene oxide was firstly prepared by using graphite as raw material.The thickness of graphene oxide nanosheet was about 1.5 nm and the lamellar size was 4 ?m,showing high quality.Graphene oxide fiber was prepared by wet spinning method.Graphene oxide nanosheets gradually shrunk into fiber in acidic coagulation bath.The charge properties of graphene oxide nanosheets and the distance between graphene nanosheets were changed in coagulation bath,resulting in the shrinkage of the initial graphene oxide fiber.After chemical reduction,many regular wrinkles were still along the outside surface of graphene fiber.The internal structure of graphene fiber was dense and layer-by-layer,which was due to the accumulation of graphene nanosheets.The elongation of graphene fiber was 3.5%and the intensity was 107.9 MPa.The electrochemical results showed the graphene fiber electrode had excellent supercapacitive behavior.The capacitance of graphene fiber electrode was 4.3 mF/cm2 at the current of 30 ?A.Besides,graphene composited fibers could be prepared by wet spinning method.Graphene oxide and PANI were mixed to form composited spinning solution.Graphene oxide-PANI composited fiber was prepared by wet spinning and then reduced to graphene-PANI fiber.Graphene-PANI composited fiber had a honeycomb-like internal structure.Graphene nanosheets were as the framework structure.PANI particles worked as the filler,which also uniformly distributed in the composited fibers.The elongation of graphene-PANI composited fiber was 7.3%and the intensity was only 28.9 MPa.The capacitance of graphene-PANI composited fiber electrode was 4.1 mF/cm2 at the current of 0.8 mA.In order to improve the properties of graphene fibers and simplify the preparation process,graphene fibers were fabricated by dry spinning method with high temperature airflow.The initial graphene oxide fiber shrunk into fiber by the effects of high temperature airflow.After reduction,many regular wrinkles were along the outside surface of graphene fibers.These wrinkles were the results of the shrinkage of graphene oxide nanosheets at high temperature airflow.The elongation of graphene fiber was 14.8%and the intensity was 127.5 MPa,showing excellent flexibility and mechanical property.The capacitance of graphene fiber electrode was 7.8 mF/cm2 at the current of 20 ?A.In addition,hollow graphene fibers were fabricated by using the coaxial system with the combination of wet spinning and dry spinning methods.Hollow graphene fiber had a complete cavity structure,and the outside surface of the cavity wall was also along wrinkles.The intensity of hollow graphene fiber was 118.5 MPa and the elongation was 3.2%.The capacitance of hollow graphene fiber was 1.6 mF/cm2 at the current of 15.8 ?A.Comparision of the chemical properties and mechanical properties of the prepared four different fibers,we chose the flexible G-Fs as raw materials to explore their apllications in supercapicitors and sensors.In order to explore the applications of graphene fibers,graphene fibers were used as electrodes to prepare parallel supercapacitor(GFS)and flexible fiber-shaped supercapacitor(FSS).The electrochemical results showed the GFS had excellent CV stability and fast charge and discharge property.After 10,000 cycles charge and discharge,the capacitance retention of GFS was about 80.1%,showing excellent stability and supercapacitive behavior.The capacitance of GFS-0.3 was 0.98 mF/cm2 at the current of 50.7 ?A.The prepared FSS demonstrated excellent flexibility and supercapacitive property.The electrochemical properties of FSS were very stable even at knotted state.The capacitance of knotted FSS was 0.21 mF/cm2 at current of 25.36 ?A,which was increased by 10.3%compared to that of the normal state FSS.FSS exhibited excellent supercapacitive performance and possessed high energy density 4.6 mWh/cm3(23.3 ?Wh/cm2)and power density 0.7 W/cm3(3.4 mW/cm2)at the current of 2.02 ?A.Wearable G-Fs sensors were prepared by graphene fibers and used to monitor human motions.G-Fs sensors showed high sensitivity,cyclic stability and accuracy in monitoring bending angles.G-Fs sensors had a large sensitivity range about 120 degree and a fast response time about 70 ms.The resistance variation of G-Fs sensor showed excellent stability,high accuracy and reproducibility at different bending rates and bending types.G-Fs sensors were attacted to different body parts to monitor human motions,such as the bending of finger,releasing and clenching of hand,and stretching of arm.The wearable graphene fiber sensor exhibited high sensitive,good reproducibility,and excellent stability in monitoring human motions.In conclusion,graphene fibers with excellent flexibilities and mechanical properties were prepared by graphene oxide solution using wet spinning and dry spinning methods.The prepared graphene fibers showed excellent performances in the application of supercapacitors and sensors.Therefore,the research results of this thesis provide theoretical basis and technical guidance for the fabrication of graphene fibers and its applications in energy storages and flexible and wearable sensors.