Flexible and Self‐Healing Thermoelectric Converters Based on Thermosensitive Liquids at Low Temperature Gradient

Abstract

electrode surface. The mechanism of thermal harvesting is similar with thermal charge of ionic solution, which is confirmed by previous researches on non-redox ionic thermally capacitive cells. [26,27] It is of importance that Seebeck coefficient (S), power factor (PF), and thermoelectric figure of merit (ZT) are three important parameters used to evaluate the thermoelectric performance of potential thermoelectric materials. To maximize the thermoelectric performance, lower thermal conductivity ( ) κ , higher electrical conductivity (σ), and S are needed according to Equation (1)Herein, we designed a flexible and self-healing thermoelectric converter based on thermosensitive liquids with low temperature gradient. Ionic liquid acting as a thermosensitive fluid was employed owing to their intrinsic merits of liquid materials. The converter generates thermoelectric potential variation of tens of millivolt under low temperature gradient on account of asymmetrically heating. Notably, ionic liquids could also be integrated with flexible substrates or functional nanoparticles to render thermoelectric converter possessing the performance of flexibility, self-healing property, and photo-thermo-electric (PTE) conversion.Four imidazolium cations with different alkyl side chain and two anions including inorganic and organic species were combined to investigate thermoelectric performances of seven ionic liquids, excluding 1-ethyl-3-methyl imidazolium hexafluorophosphate ([EMIm][PF 6 ]) behaving as solid at room temperature. A measurement setup for monitoring the realtime change of open-circuit potential of ionic liquid thermoelectric converter (ILTE converter) was constructed to evaluate the S as shown in Figure 1a,b. The ILTE converter placed on two Peltier devices was heated at left end and kept the other end unheated at room temperature (25 °C). Temperature gradient between two ends of ILTE converter was well maintained owing to poor thermal conductivity of ionic liquid, confirmed by the measured thermal conductivity and thermal imaging of infrared camera (Table 1, Figure S8 and Movie S1, Supporting Information). Typical ILTE converter filled with [EMIm][Tf 2 N] was tested for potential variation generated from alternate heating and cooling of Peltier device (Figure 1c). The potential of left electrode immediately decreases when heated left end of converter. Clearly, this phenomenon results from the different ionic mobility, and cation-anion, ion-metal interactions. With unchanged ionic arrangement on right unheated electrode, ionic rearrangement, and migration on heated end lead to the change of open-circuit potential. The potential variation of converter as the value of 42.2 mV shows the approximately same value under fixed temperature gradient of 26.3 K for six cycles, Concerns of urgent global issues on energy crisis and sustainable development have pushed researchers to find new energy sources and novel strategies to utilize the waste energy in the ambient surroundings. Thermoelectric materials are a kind of promising...

Facile Fabrication of a Self-Healing Temperature-Sensitive Sensor Based on Ionogels and Its Application in Detection Human Breath

“…The temperature-current characteristics of the ionogels were also measured and presented in Figure 4a and Figure 4b. It can be seen that the current increased with the increase of the temperature, which was consistent with reported temperature sensors based on ionogels [28]. The effects of the temperature to the current was attributed to the migration rate of ionic mobility.…”

Self‐Healable and Stretchable Organic Thermoelectric Materials: Electrically Percolated Polymer Nanowires Embedded in Thermoplastic Elastomer Matrix

“…Jo et al introduced a fluorosurfactant into conducting polymers to control the stretchability and achieved stable TE performance until 60% strain . However, mechanical self‐healing properties, i.e., the ability to recover from physical or chemical damage spontaneously or by natural environment, have not yet been demonstrated for solid‐state organic and inorganic TE materials . Given that organic materials can be easily damaged by external stimuli, self‐healing properties can greatly extend the application range of organic TE materials and also increase the production yield during device fabrication.…”

“…[22] However, mechanical self-healing properties, i.e., the ability to recover from physical or chemical damage spontaneously or by natural environment, have not yet been demonstrated for solid-state organic and inorganic TE materials. [24] Given that organic materials can be easily damaged by external stimuli, [7,25] self-healing properties can greatly extend the application range of organic TE materials and also increase the production yield during device fabrication. In particular, development of organic TE materials possessing self-healing properties and stretchability may provide a new avenue for the realization of the abovementioned next-generation self-powered electronic devices and systems.…”

Thin Film Thermoelectric Materials: Classification, Characterization, and Potential for Wearable Applications

“…However, this method is not accurate for applying to thin films due to the slow thermal response of thin films and insensitive of small transient Seebeck voltage [96]. In much research, TE data of thin films were obtained using homemade apparatus for matching samples at different characteristics [97,98]. Thus, there is no uniform measurement method for all kinds of thin film TE materials.…”