Preparation Of Metal Oxide/Graphene Composites And Their Related Properties

The shortage of natural resources and the deterioration of the ecological environment are the most concerned issues for all mankind.The new challenge that using new clean energy to replace fossil fuels to produce electricity is the efficient storage of electricity.Co3O4 presents a promising application because of the high theoretical specific capacitance and superior electrochemical properties.However,as a kind of electrode material,due to the poor conductivity and volume expansion of Co3O4,the actual specific capacitance value is much lower than the theoretical value.Therefore,the specific capacitance of Co3O4 is improved by regulating the microstructure of Co3O4 and compounding it with graphene.In addition,the harm of NO₂ to the human body and the ecological environment cannot be ignored,and the development of NO₂ gas sensor with excellent performance is particularly urgent.In₂O₃ has attracted extensive research due to its excellent chemical and thermal stability.However,its practical application is restricted due to the problem of agglomeration of the active material and the poor binding force with the substrate.In this paper,the in-situ growth strategy is used to construct a special morphology of In2O3 and composite with graphene to overcome the above problems.The specific works are as follows:（1）The Co₃O₄ material was prepared by a simple hydrothermal method.When Co（NO3）2 was used as the cobalt source and CTAB was added as the shape control agent,a two-dimensional high-porosity self-dispersing nano-"Bird’s nest"-like Co3O4 was formed.As a super capacitor electrode material,the specific capacitance of nano-"Bird’s nest"-like Co3O4 is65.3 F/g.In order to improve specific capacitance,Co3O4/reduced graphene oxide composites were grown in situ on the foamed nickel substrate by hydrothermal method.It was found that when the amount of urea was 0.1 mol and the reaction temperature was 120℃,a large number of active sites of Co₃O₄ nanoflowers could be obtained.The transparent reduced graphene oxide film was successfully coated on the surface of Co₃O₄ nanoflowers,and the specific capacitance of the composite increased to 252.5 F/g.（2）Nano-"walnut"-like In₂O₃ was grown in situ on the silver finger electrode by solution method.It was found that prism edge and groove structures with a large number of active sites could be obtained,when the mass ratio of In（NO₃）₂:NH₄F was 1:3 and the growth solution temperature was 90℃.The results of NO₂ gas sensitivity measurement showed that the response value of nano-"walnut"-like In₂O₃ to 50 ppm NO₂ at room temperature could reach 219,and the response recovery time was 89 s and 80 s,respectively,under UV-assisted irradiation.When the mass ratio of In（NO₃）₂:NH₄F was 1:3 and the hydrothermal temperature was 120℃,nano-"bread"-like In₂O₃ could be obtained,whose surface structure was showed uniform and abundant pore.It had a high response value（493）to 50 ppm NO₂ and the response recovery time was 3 s and 5 s,respectively,at the working temperature of 100℃.It also has good gas selectivity and repeatability to NO₂.The results indicated that the micro-morphology of In₂O₃,working temperature and ultraviolet light played a significant role in its gas sensing properties.（3）The In₂O₃ and graphene composites were prepared by hydrothermal method.In₂O₃ was successfully coated by graphene to form a"sandwich"structure.The gas sensing properties of graphene/In₂O₃/graphene composites showed that:the gas sensing response value of the composites to 50 ppm NO₂ increased from initial 4.7 of pure graphene to 18.4 at150℃,and the response and recovery time of the composites reduced from 52 s,283 s for pure graphene to 13 s,69 s for the composites.The reason for the improvement of gas sensitivity of composites is the formation of heterojunction between graphene and In₂O₃,the existence of In₂O₃ effectively prevented the agglomeration of graphene and provided more highly reactive sites for the adsorption of target gases.