Research On Integrated Devices For Thermoelectric Conversion And Energy Storage

Low-grade heat（<200℃）is widespread in daily life and industrial production,and it will have a dramatic impact on the economy and environment by efficiently utilized it.Thermoelectric technology directly converts thermal energy into electrical energy through the utilization of the Seebeck effect,grounded in electronic conduction,or the Thermodiffusion and Thermogalvanic effects,rooted in ionic conduction.This conversion methodology not only circumvents energy losses but also finds applicability across diverse scenarios,including industrial waste heat recovery and automobile exhaust energy recuperation.Nonetheless,the single thermoelectric conversion function renders it incapable of simultaneously achieving energy storage,necessitating its pairing with energy storage devices.This segregated system not only yields sluggish response times but also incurs additional losses during the energy conversion processes,consequently resulting in diminished thermal energy recovery efficiency and limiting its widespread application.Therefore,exploring a high-performance integrated device that can simultaneously achieve thermoelectric conversion and energy storage is urgent.Enlightened by the above consideration,this dissertation starts from the research of ionic thermoelectric device based on thermogalvanic effect.It innovatively proposes an integrated device that leverages the commonality between ionic thermoelectric conversion and electrochemical storage,and delves into the impact of pivotal factors such as device construction,electrode materials,and electrolytes on device performance.It is expected to achieve a high-performance integrated device that can realize the thermoelectric conversion and energy storage.The researches are as follows:1.Design and optimization of the ionic thermoelectric devices based on thermogalvanic effectIn response to the core challenges such as low conversion efficiency and insufficient output power faced by current thermoelectric ionic devices,this study extensively investigates the impact mechanism of thermal energy loading methods and device structure on their overall performance.Specifically,the temperature difference,average temperature difference,the direction of the temperature difference and the electrode spacing,electrolyte concentration are investigated in detail.Finally,the key indicators for optimal thermoelectric performance of i-TE devices are obtained.The testing results reveal that the open-circuit voltage depend on the temperature difference,while the short-circuit current is influenced by the temperature difference,average temperature difference,the direction of the temperature gradient,electrode spacing,and electrolyte concentration,thereby affecting the output power.The desirable short-circuit current and output power are 41.39 m A and 1.198 m W,respectively.These results lay a foundation for the construction of the integrated device of thermoelectric conversion and energy storage.2.Research on thermoelectric conversion and energy storage performance of MoSe₂-Ni Se/NF electrode materials and deviceAs the core part of thermoelectric conversion and energy storage devices,the design of electrodes with both high thermoelectric and electrochemical performance is particularly important.Herein,we have constructed a i-TE device and supercapacitor by employing the same mix-phase MoSe₂-Ni Se/NF electrode.Due to the variable valences of transition metal compounds,dual redox reactions can occur in both electrolyte and electrode,an improved Seebeck coefficient(-1.69 m V K^-1)and desirable output(0.58m W m^-2K^-2)can be achieved by（2H-1T）MoSe₂-Ni Se/NF electrode based i-TE device for thermoelectric conversion.Besides,the enhanced electronic properties and 3D network accelerate the diffusion of electrolyte ions between the active materials/electrolyte interfaces.The supercapacitor also exhibits great energy density of54 Wh kg^-1 at the power density of 806 W kg^-1 and impressive cycling stability over50,000 cycles for energy storage.All results indicate that the performance of thermoelectric conversion and energy storage is superior to the previously reported,demonstrating their application value and potential.3.Study of integrated device for thermoelectric conversion and energy storage based on precipitation-driven thermogalvanic effectAlthough the aforementioned work achieved high-performance thermoelectric conversion and electrochemical storage electrode material,it was not realized within a single device,thus not strictly classified as an integrated system.This chapter further start from the redox electrolyte,and found that the existence of precipitations can achieve the functional recycling of thermal conversion and energy storage.We proposed this strategy named precipitation-driven thermogalvanic effect for the first time.It not only improves the thermoelectric performance but also enhance the electrochemical performance.Strikingly,an improved Seebeck coefficient(-2.01 m V K^-1)and desirable output(1.41m W m^-2K^-2)can be obtained.Moreover,the energy density(459 J m^-2)is increased to474%compared with the reported highest value(80 J m^-2).Additionally,a large-area prototype module consisting of 32 units manifests an open circuit voltage of 1.7 V and exhibits an energy density of 463.9 J m^-2.This work provides a completely new and effective approach to the recycling system of high-performance thermoelectric conversion and energy storage devices.4.Performance optimization of integrated thermoelectric conversion and energy storage deviceWe adopt more strategies（including separator and different crystallization precipitates）to realize the functional recycling of thermoelectric conversion and energy storage.Besides,the thermoelectric and electrochemical performance of the integrated device are further improved.It can be proved that the natural diffusion of potassium ferricyanide and potassium ferrocyanide in the solution is hindered by the additives(separator addition,supersaturated 0.7 M[Fe（CN）₆]^4-/[Fe（CN）₆]^3-precipitation and additionally KCl,K₂SO₄,Gdm Cl crystallization precipitation),leading to the realization of electrochemical energy storage.These approaches validated the broad applicability of the integrated devices based on precipitation-driven thermogalvanic effect.Moreover,when Gdm Cl precipitate was used as the additive,the device owns the best thermoelectric and electrochemical performance.It exhibits high absolute Seebeck coefficient of 3.31m V K^-1 and the maximum output power of 2.09 m W m^-2K^-2,as well as the energy density of 507 J m^-2.In summary,this thesis proposes a strategy for integrated thermoelectric conversion and electrochemical energy storage based on the fundamental structure of ionic thermoelectric devices.Various high-performance integrated devices based on the precipitation-driven thermogalvanic effect have been successfully obtained,validating the feasibility and wide applicability of this approach.This lays the foundation for further enhancing the performance of integrated devices in the future.