| In today’s society,energy crisis is a serious problem affecting the development of modern society.However,the current mode of energy conversion and utilization leads to the generation of a large amount of waste heat and waste heat during production and operation.Recovery and recycling of waste heat can improve the energy efficiency of our society,which makes thermoelectric generation technology attract more and more attention.The thermoelectric effect of generating voltage difference under temperature difference is a means suitable for waste heat utilization.The waste heat utilization technology using thermoelectric effect has the characteristics of no moving parts,no noise,no chemical reaction and zero gas emission,and has a good application prospect.According to the types of carriers,thermoelectric materials can be divided into ionic thermoelectric materials and electronic thermoelectric materials,and their ability to generate thermal voltage at a certain temperature difference is evaluated by Seebeck coefficient.The Seebeck coefficient of ionic thermoelectric materials is larger than that of electronic thermoelectric materials under the same conditions.Therefore,the characteristic that ionic thermoelectric materials can obtain large thermal voltage through the series connection of fewer components has attracted wide attention.The carriers of ionic thermoelectric materials are anions and cations.If the thermal diffusion ability of anions and cations is the same,thermal voltages with the same magnitude and opposite directions will be generated inside the thermoelectric materials,but no voltage will be displayed to the outside.A large number of studies have shown that the interaction between ions and polymers is one of the effective ways to differentiate the thermal diffusion ability of anions and cations,which can improve the Seebeck coefficient of ionic thermoelectric materials to a certain extent.However,the existing researches mostly focus on a single ion,and the mechanism explanation of how ions affect the Seebeck coefficient of the system is unclear.At the same time,the existing ionic thermoelectric material system is mostly water system,and the evaporation of water will reduce its dissociation degree,resulting in the degradation of thermoelectric performance of the system.In view of the above problems,this paper explores the mechanism of cation’s influence on Seebeck coefficient by building a test platform,using a variety of chloride cations and taking their softness parameters as evaluation conditions.At the same time,this paper replaces the existing salt solution system with low volatility ionic liquid,tests its related properties through experiments,and explores the mechanism of the influence of ionic liquid on Seebek coefficient.The main work of this paper is as follows:（1）Construction and calibration of Seebeck coefficient test platform.In this paper,a test system suitable for Seebeck coefficient testing is built based on the characteristics of slow ion migration.The stable and simple single-ion conductor polystyrene sulfonic acid is used as the standard sample and compared with the existing reports.The influence of the shape and size of the electrode used in the test,the electrode material and the collection rate during data collection on the Seebeck coefficient is also explored.The experimental results show that the size of the electrode used has a more accurate test result when the width is 1 mm and the spacing is 2 mm.When the electrode material is silver or copper,the test result will not be affected.The test result of polystyrene sulfonic acid is 7.9 m V/K,which is very close to the previously reported value of 8 m V/K.When the data collection rate is 5 power line cycles,it can take into account the data collection time and the amount of noise.（2）To explore the influence of cation softness parameters on ion Seebeck coefficient.In this paper,poly（3,4-ethylenedioxythiophene）:poly（styrene sulfonate）（PEDOT:PSS）and a mixture of inorganic water-soluble chloride salts are used to explore the effect of cations on the Seebeck coefficient from an ionic point of view.Pure PEDOT:PSS has a Seebeck coefficient of 8.98 m V/K.Studies have found that when the softness parameter of cations is positive or close to positive,the cations in the chloride salt will be captured by PSS,such as copper ions,indium ions and nickel ions.Therefore,the Cl-is the main carrier in the mixture,resulting in a negative Seebeck coefficient.The In3+with a softness parameter of 0.58 produces the largest negative Seebeck coefficient,which is-9.63 m V/K.Then a robust ionic thermoelectric device was prepared.This work highlights the important role of ion properties in manipulating the Seebeck coefficient and provides guidance for the selection of ions in ionic thermoelectric materials.（3）To explore the influence of ionic liquid on ionic Seebeck coefficient.In this paper,the above work was optimized,and polymer poly（vinylidene fluoride-hexafluoroethylene）（PVDF-HFP）and ionic liquid were selected to prepare ionic gel.The environmental friendliness and low volatility of ionic liquids also reduce the influence of environment on ionic thermoelectric devices.In this paper,the thermoelectric properties of ionic gels prepared by different ionic liquids were investigated.The experimental results show that the interaction between ionic liquid and polymer will promote the crystalline conformation of polymer PVDF-HFP to change fromαphase toβphase.The interaction between fluorine groups on PVDF-HFP and anions in ionic liquid limits the migration of anions,and promotes the difference of thermal diffusion ability between anions and cations.In this paper,the morphology,crystal conformation,pore size distribution and conductivity of ionic gel were tested and analyzed by scanning electron microscopy,Fourier transform infrared spectroscopy,mercury intrusion method and AC impedance spectroscopy.The Seebeck coefficients of ionic gels with different ionic liquids are different due to the difference of ion migration caused by pore size.The research content of this topic provides ideas for preparing ionic gel thermoelectric materials. |
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