Soret Effect of Ionic Liquid Gels for Thermoelectric Conversion

Abstract

Cations and anions can accumulate at the two ends of an ionic conductor under temperature gradient, which is the so-called Soret effect. This can generate a voltage between the two electrodes, and the thermopower can be higher than that of the electronic conductors because of the Seebeck effect by 1–2 orders in magnitude. The thermoelectric properties of ionic conductors depend on the ionic thermopower, ionic conductivity, and thermal conductivity. Compared with other ionic conductors, like liquid electrolytes and hydrogels, ionogels made of an ionic liquid and a gelator can have the advantages of high thermopower and high stability. Great progress was recently made to improve the ionic conductivity and/or ionic thermopower of ionogels. They can be used in ionic thermoelectric capacitors (ITECs) to harvest heat. In addition, they can be integrated with electronic thermoelectric materials to harvest heat from both temperature gradient and temperature fluctuation, which can be caused by waste heat.

A bionic self-driven retinomorphic eye with ionogel photosynaptic retina

“…The Δ T and Δ U value both monotonically increase with increasing dopant concentration, because the similar evolution trends are observed in the time-dependent Δ T and corresponding Δ U characters. This behavior is consistent with the Soret effect 22 , 23 , the voltage gradient is linearly proportional to the temperature gradient, with a relationship described as , where S is the Soret coefficient, which normally determines the magnitude of thermodiffusion in ionogel, with a value of 1.57 mV K −1 at 1.0 mg mL −1 doping concentration (Fig. 2e ).…”

Organic iontronic memristors for artificial synapses and bionic neuromorphic computing

“…63,64 Due to their exceptional chemical stability and precise control over ions, ionic liquids have also been extensively studied and applied in the fields of solar cells and flexible fuel cells, while they can also be prepared into thin films for metal protection, electronic device packaging, biomedicine, and so on. 65–67 In addition, OIMs can be applied in the domains of configurable circuits and multilevel memory, owing to their adjustable molecular structure, excellent optoelectronic properties, large specific surface area, controllable porosity, etc . 68–70 Overall, the unique characteristics of OIMs enable them to exert excellent performance and application in diverse fields, thereby manifesting their significance for further development and investigation in the future.…”

Intelligent ion gels: Design, performance, and applications

“…Reproduced with permission: Copyright 2022, American Chemical Society. 71 gels can be excited to fluorescence at 615 nm (red light) under UV light. By adjusting the ratio of the two fluorescent components, the fluorescence wavelength can be freely adjusted in the range of blue to red light (Figure 6B).…”

“…The phenomenon of thermal diffusion of ionic components from the high‐temperature end to the low‐temperature end under a temperature gradient is called the Soret effect (Figure 5G). 71 It is known that the migration rates of different anions and cations of ionic components are different due to the differences in volume and functional groups, and so on. This leads to differences in the concentrations of anions and cations at the cold and hot ends.…”

“…(G) Illustration of the Soret effect. Reproduced with permission: Copyright 2022, American Chemical Society 71 …”