Synthesis Of Binary Metal Oxide Nanostructures And Their Energy Storage And Gas Sensing Properties

With the rapid development of social technology,people's demand for electronic equipment is getting higher and higher.In recent years,emerging flexible/wearable electronic products such as smart watches,electronic textiles,portable medical devices,biosensors and Internet systems are increasingly entering our daily lives.In order to adapt to the development,as an important component of electronic equipment,the development of energy devices and sensors is also imminent.Because of their unique physical and chemical properties,binary metal oxide nanomaterials show great application prospects in energy storage such as supercapacitors,Li ion batteries and sensor components.It is of great significance to prepare small size and high quality binary metal oxide nanomaterials and further study the properties of such materials so as to make them play a more important and comprehensive practical role in solving energy and environmental problems.In this thesis,a variety of binary metal oxide nanostructures,such as MnCo2O4@CC and ZnCo2O4@CC three dimensional nanosheet arrays,ZnCo2O4 nanowires and SrGe4O9 nanotubes,were prepared by physical method and chemical method.Their properties in energy storage and gas sensing were further systematically studied.On the basis of the above work,an integrated system of asymmetric supercapacitor and various sensors with fork finger structure is made,and its application as a power supply unit in the self-powered integrated sensor system is verified.The main research results of this paper are as follows:Firstly,using Co-MOF as template,MnCo2O4 and ZnCo2O4 three-dimensional nanosheet array structures were synthesized on carbon cloth by combining MOF template and calcination process.The results show that both electrode materials have excellent electrochemical properties.(1)In the three-electrode system,the mass capacitance of MnCo2O4 is 792.3 F g-1 when the current density is 2.5 mA cm2.The mass specific capacity of ZnCo2O4 is 766.8 F g-1 at the same current density.After 20,000 cycles,the specific capacitance of MnCo2O4@CC electrode still maintain 95.5%,and that of ZnCo2O4@CC electrode maintain 94.7%.Based on this,we encapsulated MnCo2O4@CC and ZnCo2O4@CC respectively and synthesized carbon nanosheet array @ carbon cloth(CNS@CC)to assemble asymmetric supercapacitor devices whose voltage window can reach 1.55 V.The maximum energy density of MnCo2O4@CC//CNS@CC asymmetric supercapacitor is 25.6 Wh kg-1(power density is 3.4 kW kg-1).Meanwhile,the energy density of ZnCo2O4@CC//CNS@CC capacitor is 22.7 Wh kg-1(4.1 kW kg-1).(2)The lithium storage performance of MnCo2O4@CC and ZnCo2O4@CC nanosheet arrays as anode materials for Li ion batteries was also studied.The results show that:The reversible capacity of MnCo2O4@CC nanosheet array is 1682.2 mA h g-1 at a current density of 1 A g-1,and the capacity retention rate is 75.5%after 250 cycles.As the current density increases from 0.5 A g-1 to 10 A g-1,the output specific capacity decreases from 1750.8 mA h g-1 to 409.7 mA h g-1.When the current density is restored to 0.5 A g-1,the specific capacity reversibly recovers to 1785.5 mA h g-1,indicating that the prepared material has good rate performance.In addition,the specific capacitance of ZnCo2O4@CC nanosheet array is 1560 mA h g-1 at the current density of 1 A g-1,and the capacity retention rate is 71.4%after 250 cycles.In summary,it can be seen that both MnCo2O4@CC and ZnCo2O4@CC exhibit excellent electrochemical properties.Second,ZnCo2O4 nanowires with a diameter of about 200 nm were successfully prepared by electrospinning and calcination process.and a low-cost mechanical scribing method was designed to make micro-supercapacitors.It is found that a single device can deliver a high area energy density of 0.065 ?Wh cm2 and power density of 0.092 mW cm-2.In addition,the micro-supercapacitor obtained has high mechanical stability,with only 1%capacitance change after 2000 mechanical bending cycles.Through integration with the CdS nanowire-based photodetector,a self-driven microsystem configuration is realized.The feasibility and potential of the self-driven microsystem in the same plane are demonstrated by using the planar micro-supercapacitor as the power supply and the photoelectric detector as the conventional functional detection unit.Thirdly,SrGe4O9 nanotubes were synthesized by using the electrospinning and calcination process in the work.The synthesized SrGe4O9 nanotube has a diameter of about 150 nm and can be used as an ammonia detection material at room temperature.At room temperature,the maximum response value of SrGe4O9 nanotubes to 100 ppm NH3 is 2.49.We successfully modified SrGe4O9 nanotubes to form Pt-SrGe4O9 nanotubes by reducing H2PtCl6 to Pt by heating method,and the sensing response value of the modified Pt-SrGe4O9 nanotubes is increased to 7.08.Pt-SrGe4O9 nanotubes has a response concentration range of 1-500 ppm compared to SrGe4O9 nanotubes in the range of 1-300 ppm.The flexible gas sensor made of Pt-SrGe4O9 nanotubes has a response value of 5.04 in 100 ppm NH3 atmosphere.Moreover,the flexible devices have the same response recovery period at different bending angles(including 0°,30°,60°,90°,120° and 150°),showing good flexibility and stability,indicating their potential applications in the field of flexible and wearable electronics.Finally,In the fourth work,we use graphene microplates(GNPs)as active materials and fluid collectors.In the combination of mechanica! scratching technology and electrodeposition technology,we produce asymmetric microsupercapacitors with one electrode GNPs@MnO2 and the other electrode rGO@GNPs.The results show that the voltage window of the MnO2@GNPs//rGo@GNPs asymmetric micro-supercapacitor can reach 1.6 V,which is twice that of the pure GNPs symmetric micro-supercapacitor(0.8 V).The area ratio capacitance of the asymmetric micro-supercapacitor can reach 12.5 mF cm-2 at the current density of 0.1 mA cm-2,the area specific capacitance of the symmetric micro supercapacitor is only 150 ?F cm-2 at the same current density,the area specific capacitance of asymmetric micro-supercapacitor is 83.3 times higher than that of symmetric devices.The prepared asymmetric micro-supercapacitor has good cycle stability,and its capacitance still remains 89.8%of its initial value after 10000 cycles at the current density of 1 mA cm-2.The mass produced 4S*4P array device can easily drive nine LED lights.We further extend its application by using four series asymmetric micro-supercapacitors connected in series to form four selfactuated sensor units,which successfully drive four different sensors at room temperature,proving the feasibility and potential of multi-functional self-actuated micro-system.