Study And Fabrication On Novel Energy-Supply Devices For Low-Power Sensors In Agricultural Internet Of Thing

In order to promote and improve our country's agricultural modernization,agricultural Internet of Thing(AIo T)has been listed as one of the priority development directions of modern agriculture.Generally,AIo T,which is composed of three layers,including agricultural parameter monitoring sensing(sensors),signal transmission(signal transmission devices)and system application(system decision and executors),is a technology to achieve refined,intelligent and automated management of farmland based on the perception,monitoring,transmission and analysis of crop environment and physiological parameters for obtaining and executing control commands.Among them,various sensors,used to sense and monitor the environment and physiological parameters of crops,are the bottom devices of AIo T,which are driven by vast energy-supply devices(including batteries and circuits,etc.).The reliability and stability of AIo T would be significantly influenced by the stable operation of these energy-supply devices.With the development of low-power sensors,the approach of the energy crisis and the increasing awareness on eco-development and environmental protection,new requirements,including miniaturization and integration,low energy consumption(low fossil energy consumption)and green,are put forward for the future AIo T.In addition,with the need to extract more types of crop physiological parameters,energy-supply demands on the irregular structure(such as:plant stem and leaves surface,etc.)of AIo T are gradually increasing.Therefore,in this research,we have designed and fabricated new energy-supply devices(including new energy-storage devices,new energy harvesting and conversion devices)for the low-power sensors in AIo T to meet flexibility,miniaturization and integration,low energy consumption and green,etc.The main research content and results of this thesis are listed as follows:(1)Fabrication of conducting polymer-based flexible energy-storage electrodeIn this study,a flexible energy-storage electrode based on conducting polymer was designed and fabricated to meet the energy-supply demand for low-power sensors on the irregular structure of AIo T.The flexible energy-storage hybrid electrode was composed of flexible,high-conductivity,high-capacitance PEDOT:PSS and high-stability,low-conductivity 2H MoS₂nanosheets.The results presented that the crystal stcuture of MoS₂ nanosheets remained baseically unchanged and the content of PSS chains was greatly reduced after electrode preparation and concentrated-H₂SO₄ post-treatment.Next,when the mass ratio of 2H MoS₂ to PEDOT:PSS was10%,the 2H-P-H-10 hybrid electrode had the highest capacitance performance with 89 F g^-1@0.1 A g^-1,indicating superior capacitance performance.Then,the capacitance of 1T and 2H MoS₂nanosheets hybrid electrodes were basically same with the mass ratio from 0%to 10%,while the capacitance of 1T MoS₂nanosheets hybrid electrodes were higher than that of 2H MoS₂nanosheets hybrid electrodes with the mass ratio from 20%to 40%,indicating that the capacitance of 2H MoS₂ nanosheets was mainly influenced by the conductivity of hybrid electrodes.Meanwhile,after 4000 GCD cycles,the capacitance retention of 2H-P-H-10 hybrid electrode reached 98%,demostrating long life and good stability.Finally,a sandwich-like supercapacitor,loacated on the plant leaves surface,was fabricated with 2H-P-H-10 hybrid electrode to realize continuous energy supply for low-power LED.Thus,2H-P-H-10 hybrid electrode is a flexible and high-performance energy-storage electrode,which has great prospects as the energy-supply device for low-power sensors on the irregular structure of AIo T.(2)Fabrication of graphene-based flexible and miniaturized energy-storage deviceIn order to further improve the miniaturization and integration of energy-storage device on the basis of section(1)to facilitate mass production,a flexible,high-performance,asymmetric,in-plane,interdigitated micro-supercapacitor(MSC)was designed and fabricated.The FGO-FrGO MSC was composed of electrochemical-exfoliated FGO nanosheets and chemical-reduced FrGO nanosheets.The results performed that there were abundant functional groups on the surface of FGO and FrGO nanosheets,and the functional groups of two nanosheets were different.Secondly,good flexibility of FGO-FrGO MSC was exhibited under bending and twisting.Next,the highest area specific capacitance of FGO-FrGO MSC,7.3 m F cm^-2@5 m V s^-1,was performed.In addition,after 5000 GCD cycles,the capacitance retention of FGO-FrGO MSC basically remained 100%,indicating that FGO-FrGO MSC had a long service-life and excellent cycling stability.Finally,“three series and three parallel”MSCs,placed on the plant leaves,were fabricated to continuously energy supply for the low-power temperature and humidity sensor in AIo T.In conclution,FGO-FrGO MSC is a flexible,high-performance and miniaturized energy-storage device that has great prospects to be used as the miniaturized energy-supply device integrated with low-power sensors in AIo T.(3)Fabrication of filter paper-based nanogenerator for rainwater energy harvesting and conversionThe energy-storage devices,designed and fabricated in section(1)and(2),could not solve the problem of high fossil energy consumption in AIo T.In order to meet the requirement of low-energy consumption,a filter paper-based nanogenerator(FPNG)was designed and prepared to harvest and convert rainwater energy into electric energy.It was indicated that the Zeta potentials of filter papers(-25 m V)and the modified MWCNTs ink slurry(-54.7 m V)were characterized to be negative,revealling that the positive ions in rainwater were absorbed with negative ions in filter papers to form a double-electric layer and the absorption capacity of filter papers could be enhanced by the modified MWCNTs ink slurry.Next,the working conditions of FPNG were optimized,presenting that the highest open-circuit voltage of FPNG was induced from dropping1 m M Na Cl solution at 20 m L h^-1 injection speed on quantitative medium speed FPNG with 75°placement angle,and the streaming potential,streaming current and power of FPNG were 2.09±0.121 m V,4.75±0.0725 n A and 9.91±1.39 p W per drop,respectively.Furthermore,FPNG was used to harvest and convert the rainwater energy,and the streaming voltage,streaming current and power can be obtained as 0.698±0.0056 m V,3.3±0.55 n A and 2.4±0.65 p W per drop,respectively.Finally,FPNG was placed on the surface of plant leaves to harvest and convert the rainwater energy,which had different streaming voltage responses to different rainfall.Therefore,the feasibility of FPNG for rainwater energy harvesting and conversion is verified.The prepared FPNG can provide a low-fossil-energy-consumption energy-supply device based on rainwater energy harvesting and conversion for the low-power sensors in AIo T.(4)Fabrication of pullulan hybrid film-based TENGIn order to reduce the environmental influence of AIo T on the basis of section(3)and to explore the application of natural biopolymer materials on energy harvesting and conversion,a pullulan film-based TENG was designed and prepared.The preparation process of pullulan film was simple and green.It was showed that the pullulan-based films were highly transparent and flexibile.With the addition of BSA,CMC and GLA,the tensile properties of pullulan-based films were significantly improved.Next,the electric properties of pullulan-based films with the addition of different additives were improved.It was presented that the open-circuit voltage of P-P TENG was lowest,43 V,while the open-circuit voltage of F-P TENG was highest,79 V.With the 7 M?load resistance,P-P TENG had the largest output power density,41.7 m W m^-2.And during 1000s long-term cycling test,the open-circuit voltage of P-P TENG remained basically unchanged.Once more,open-circuit voltage of P-P TENG was basically same during 5 cycles.Moreover,a29 LED series array had been successfully lightened by P-P TENG and various human hand bending movements had been monitored by F-P TENG.Finally,mechanical energy,generated by the wind-blown leaves,was successfully harvested and converted by P-P TENG,located on the surface of plant leaves.Meanwhile,“three series and three parallel”MSCs,fabricated in section(2),were charged by P-P TENG and were used to enegy supply for the low-power temperature and humidity sensor in AIo T.In summary,green energy(disorder and tiny mechanical energy in agricultural system)is harvested and conversed by a flexible,high-performance,recyclable and green pullulan film-based TENG,providing a green energy-supply device to drive low-power sensors in AIoT.