Synthesis And Electrocatalytic Properties Of Composites Based On Multidimensional Graphene Materials

Due to its large specific surface area,excellent electrical conductivity and good stability,graphene is considered to be a nearly perfect electrochemical substrate.However,as the catalytic activity of graphene is not high,it is usually used as the substrate to compound the nanomaterials with high activity but easily aggregate.The large specific surface area of graphene can provide adequate anchor sites for homogeneous dispersion of nanoparticles,and it can also effectively improve the intrinsic properties of the materials.Therefore,the composite materials can show synergistic effects of single component,and show extraordinary application prospects in many fields,especially in electrochemistry.However,although graphene nanocomposites have many advantages,researchers have found a common problem in this kind of material,that is,the accumulation and aggregation of lamellae are easily affected by the interaction of?-?and Van der Waals force between different graphene layers,which causes the composite material to have a sharp surface area reduced and the performance faded.Therefore,how to effectively avoid the accumulation and agglomeration of graphene matrix composites has become a very meaningful research topic.The purpose of this thesis is to build nanocomposites based on graphene by simple methods.Through the introduction of hetero atoms,self assembled with graphene-like two dimensional materials and cross-linking construction of three-dimensional structures,a composite with a certain spatial structure is formed and high performance electrode materials with synergy effects of graphene and different materials are constructed.The main contents of this paper are divided into the following four aspects:1.A simple solvothermal method was used to synthesize the NG/Mn₃O₄composite.From the SEM images,it was found that the NG showed a curly wave in the space,and then the composite material was modified onto the electrode to study the electrocatalytic properties of H₂O₂.The results show that the dispersion and conductivity of Mn₃O₄ is improved and the catalytic activity of Mn₃O₄ are increased with the introduction of nitrogen doped graphene.The response of composite modified electrode to H₂O₂ shows a wide linear range,low detection limit and high sensitivity,which is expected to develop into a low-cost and efficient H₂O₂electrochemical sensor.2.MoS₄^2-was adsorbed by ethylamine modified GO,then in situ reduced and founded on the surface of graphene to form a layered heterogeneous stacked MoS₂/rGO composite structure.Due to the limitation of graphene and ethylenediamine,the number of stacking layers in the direction of C axis of MoS₂ is few.The coverage of MoS₂ also increases the interlayer space between different graphene to a certain extent and reduces the stacking of graphene,which helps improve the composite with high overall conductivity.After the Au NPs were modified by electrodeposition on the surface of the composite modified electrode,the single strand DNA probe molecules modified by sulfhydryl group could be assembled by the covalent bond of"S-Au-S".Methylene blue was used as an electrochemical indicator,and the number of methylene blue adsorption was influenced by the number of complementary base pairs.Thus,the peak current of methylene blue oxidation was changed and the matching degree of DNA base sequence was indirectly reflected as a reference.The method can be used to determine the target DNA and the probe DNA,they complement each other relatively simply and quickly.The composite material with high conductivity and high ratio provides a sufficient connection site for the DNA probe,and the covalent bonding is also beneficial to the rapid transmission of the electrons,making the method highly sensitive for the detectin of known sequence,which will be of high practical value.3.3D rGO/CoS₂ composite was synthesized by a simple solvothermal method.The formation of three dimensional body structure was clearly observed regardless of the macroscopic appearance or microstructure.The sponge-like porous three-dimensional cross-linking structure greatly reduces the stacking and agglomeration between graphene,and the rich pore structure provides convenience for the mass transfer process in the solution.As a contrast experiment,the 2D rGO/CoS₂ was synthesized with the same load,and the electrochemical catalytic oxidation of hydrazine was compared.The results showed that the catalytic performance of the three dimensional composite structure was obviously higher than that of the two-dimensional structure composite,which fully reflected the superiority of the three-dimensional structure.4.The MoS₂/Co₉S₈/rGO composite composite was transformed into a three-dimensional composite structure by two steps,and CNTs were introduced to optimize the distribution of non-uniform and spatial faults in the process of structural transformation.In the experiment,the spatial structure and the specific surface area of the material were observed by means of SEM and BET,and the composite material was used as the electrode material for the electrochemical hydrogen evolution.Through a series of electrochemical tests and combination with characterization results,the reasons for the optimal catalytic activity of the three-dimensional composite structure are deduced from the electrochemical level,and the stability and catalytic activity of the experimental composite materials are excellent because of the protection of the carbon materials,which can serve as an efficient pH ubiquitous electrification of hydrogen evolution catalyst.In addition,the method of transforming the two step CNTs into three dimensional structure is considered to have a certain universality,and can be extended to the construction and transformation of multistage graphene based composites in other fields.