Synthesis And Electrochemical Performance Of Graphene And Doped Graphene Electrode Materials

Graphene,a carbon material of a two-dimensional honeycomb structure formed by sp² hybridized carbon atoms,presents excellent physical and chemical properties.In recent years,graphene as e lectrode materials has been used in electric energy storage devices.The properties of electrode materials directly influence the electrochemical performance of the supercapacitor.However,the preparation methods and the composite form o F·graphene have great influence on the structure of the graphene,and thus infact the electrochemical properties of the graphene-based electrode materials.This thesis focuses on the synthesis and performance tests of the graphene-based electrode materials,including graphe ne oxide?GO?,heteroatom doped graphene and the graphene/transition metal sulfide composite.The main results are shown as follows:?1?Using graphite as a raw material,the graphene oxide?GO?was prepared by the improved method and the modified Hummers method,then reduced by hydrothermal treatment to obtain a three-dimensional graphene hydrogel?RGOHs?without reducing agent;The effects of the oxidation degree o F·gO and the temperature of hydrothermal reaction on the microstructure and electrochemical properties of the RGOHs were investigated.The results show that the preparation method has effect on the oxidation degree o F·gO,and further infacted the reduction degree of the RGOHs.The GO prepared by the improved method has a higher degree of oxidation than that obtained by the modified Hummers method.When the hydrothermal temperature is 150?,the three-dimensional graphene hydrogel presents a porous structure and a high degree of reduction.It also has the best specific capacitance of 329.5 F·g^-1 and an outstanding rate performance.?2?Using graphite and hydrofluoric acid as raw materials,the three-dimensional fluorine-doped graphene hydrogel?F-RGOHs?electrode material was prepared by chemical oxidation and then hydrothermal reduction.The effect of the hydrothermal reaction temperature on the fluorine content and the doped form of F-atom in the F-RGOHs was investigated.The relationship between the fluorine content and the electrochemical properties of the F-RGOHs?non-binder non-conductive agent?was discussed.The results show that the reduction degree of F-RGOHs and the doped form of F atoms can be controlled by the temperature of the hydrothermal reaction.The fluorine-doped graphene hydrogel electrode material?non-binder non-conductive agent?prepared at the hydrothermal reaction temperature of 150??F-RGOH-150?has a porous mesh cross-linking structure,and exhibits better electrochemical performance.F-RGOH-150?non-binder non-conductive agent?has a specific capacitance of 230F·g^-1 at a current density of 0.5 A·g^-1,which is higher than that of the RGOH?no binder non-conductive agent?.When the current density was increased to 20 A·g^-1,the capacitance can be maintained at 60%.In addition,the specific capacitance of the F-RGOH-150 electrode material was maintained at 96.2%after 2000 cycles at a scan speed of 100 mV·s^-1.?3?Using GO prepared by improved method as a raw material,acetonitrile,urea,ammonia water,N,N-dimethylamino-amine?DMF?as nitrogen-containing reagents,the three-dimensional nitrogen-doped graphene hydrogel?N-RGOHs?electrode material was prepared by a si mple hydrothermal method.The influence of different nitrogen sources on the N-atom doped form and the microstructure of the electrode materials were investigated.The relationship between the composition,microstructure of the electrode materials and the electrochemical properties were discussed.The results show that the doped form of N atom plays a leading role in the electrochemical performance of N-RGOHs,and the structure with multi-fold and multi-defect is easy to conduct electron,the transmission efficiency of the electrode materials can be improved.The nitrogen-doped grapheme hydrogel?N-RGOH-1?electrode material using acetonitrile as nitrogen source has good crystal lattice structure,high graphitization degree,multi-fold multi-pore structure,and the best electrochemical performance.The specific capacitance of N-RGOH-1 is 352.1 F·g^-1(0.5 A·g^-1).After 2000 charge and discharge cycles,the specific capacitance of N-RGOH-1 was still 85%,indicating that N-RGOH-1 has better cycle stability.The nitrogen-doped grapheme hydrogel?N-RGOH-2?electrode materialusing urea as nitrogen source has an excellent rate performance.When the current density increased to 10 A·g^-1,the specific capacitance retention rate can reach 63%.?4?Using GO as a raw material,L-cysteine as a sulfur source,sodium molybdate molybdenum source and acetonitrile as a nitrogen source,MoS₂/N-doped graphene?MoS₂-NRGOs?porous composite electrode material was prepared through a one-step hydrothermal method,The effects of the proportioning of Na₂MoO₄ and L-cysteine on the micro-morphology and electrochemical properties of the composite electrode materials were investigated.The results show that the hydrothermal pressure can affect the growth direction and micro-morphology of MoS₂.MoS₂ nano-clusters which formed by a multi-fold porous structure was loaded on the surface of N-doped graphene?NRGO?.The NRGO inhibited the expansion and contraction of the MoS ₂ in the electrochemical reaction.The multi-channel multi-fold MoS₂/N-doped graphene?MoS₂-NRGO-2?electrode material prepared by 0.5 g Na ₂MoO₄ and 1 g L-cysteine has a low defect degree and an optimal electrochemical characteristic.Its specific capacitance value could reach 427.4 F·g^-1 when the current density is 0.5 A·g^-1;When the current density was increased to 10 A·g^-1,the specific capacitance can still be maintained initial 46.7%.