Advances in Ionic Thermoelectrics: From Materials to Devices

Abstract

technology, which can literally convert ambient heat into high value-added electricity. [2] Compared to its analogous heatto-electricity technologies, TE takes the advantage of light weight, quietness, zero pollution emission, and an infinite lifetime (Figure 1b), making it ideal for selfpowering applications that are equipped on human body or installed in rural areas. [3] The performance of TE devices is mainly governed by the dimensionless figure-of-merit of their constituent TE materials, defined as ZT = S 2 σT/κ, where T refers to absolute temperature, S, σ, and κ are the Seebeck coefficient, electrical conductivity, and thermal conductivity, respectively. [4] Practically, "Z" reflects the premise of TE materials being used for power generation, namely as a thermoelectric generator, while "T" regulates the working temperature under which heat transfer is valid. [5] As can be seen in Figure 1c, TE materials with high heat transfer property and a Z of >10 −3 K −1 (corresponds to ZT > 0.3 at room temperature) are suitable for making temperature sensors; in comparison, TE materials with a much higher Z of 10 −2 K −1 (corresponds to ZT > 3 at room temperature) and low heat transfer property are preferable for making wearable devices.On the attainment of satisfactory Z value, a large S, which is proportional to the magnitude of thermovoltage per temperature difference (∆T), is highly desirable. However, the S of conventional electronic thermoelectric (e-TE) materials is limited to an order of 10 1 -10 2 µV K −1 due to relatively low electronic enthalpy of inorganic materials, i.e., the S of electron gas is merely ≈87.5 µV K −1 at room temperature. [6] Considering a small ∆T of 20 °C as that between human skin and ambient environment, more than 100 inorganic TE legs are required to work comparably with a 1.5 V solid battery via calculation, which indicates that e-TE materials are unsuitable for low-grade (<130 °C) applications. As most of waste heat is emitted from low-grade sources such as industrial plants and vehicle exhaust, traditional e-TE devices are in niche market. As another form of charge carrier, ions can induce a much larger S in an order of a few mV K −1 due to higher ionic enthalpy than electronic enthalpy. [7] As a result, an ionic thermoelectric (i-TE) device needs only ≈8 legs to generate a 1.5 V voltage at a ∆T of 20 °C, indicating that i-TE device is feasible for microminiaturization and can be incorporated with wearable devices and electronic skins. Other advantages of i-TEs over e-TEs include i) good flexibility stemming from the normally organic matrix, As an extended member of the thermoelectric family, ionic thermoelectrics (i-TEs) exhibit exceptional Seebeck coefficients and applicable power factors, and as a result have triggered intensive interest as a promising energy conversion technique to harvest and exploit low-grade waste heat (<130 °C). The last decade has witnessed great progress in i-TE materials and devices; however, there are ongoing disputes about the inherent fundamentals ...

Tailored Side-Chain Engineering and Extended π-Delocalization for Expediting Polarity Switching of Indaceno[1,2-b:5,6-b′]dithiophene-Based Conjugated Polymers

“…According to the Chabinyc’s empirical model of prior TE data, − σ is usually inversely correlated to S . , It is meaningful to present the trend of σ as a function of S during the polarity switching process. As to the D–D CPs, the values of σ gradually increased with the decreased S before the polarity switching (Figure a–c).…”

Unlocking the potential of metal halide perovskite thermoelectrics through electrical doping: A critical review

“…Halide ions can actively participate in redox reactions at the interface with the metal electrode, resulting in electrochemical reactions at the electrode/channel interfaces, 114 which can significantly impact both the stability and performance of thermoelectric devices. However, we propose that this property can be harnessed to generate electrical power via the thermogalvanic effect, 115 in which the migration of mobile halide ions can create an electrochemical potential difference when subjected to a temperature gradient, subsequently generating electrical power, if properly controlled. Exploiting the thermogalvanic effect in MHPs could open new routes as a low‐cost material for solid‐state thermogalvanic energy conversion.…”

Hierarchically Porous Cellulose Membrane via Self‐Assembly Engineering for Ultra High‐Power Thermoelectrical Generation in Natural Convection

“…These features render it an ideal choice for self-powered applications integrated into electronic devices or human bodies. [14][15][16] Notably, temperature gradient (ΔT) is essential for high-performance TET. A high ΔT is crucial for generating high-power output, as evidenced by the equation P = (SΔT) 2 /4R, [17] where S and R are the Seebeck coefficient and electrical resistance, respectively.…”