Unconventional Thermoelectric Materials for Energy Harvesting and Sensing Applications

Abstract

Heat is an abundant but often wasted source of energy. Thus, harvesting just a portion of this tremendous amount of energy holds significant promise for a more sustainable society. While traditional solid-state inorganic semiconductors have dominated the research stage on thermal-to-electrical energy conversion, carbon-based semiconductors have recently attracted a great deal of attention as potential thermoelectric materials for low-temperature energy harvesting, primarily driven by the high abundance of their atomic elements, ease of processing/manufacturing, and intrinsically low thermal conductivity. This quest for new materials has resulted in the discovery of several new kinds of thermoelectric materials and concepts capable of converting a heat flux into an electrical current by means of various types of particles transporting the electric charge: (i) electrons, (ii) ions, and (iii) redox molecules. This has contributed to expanding the applications envisaged for thermoelectric materials far beyond simple conversion of heat into electricity. This is the motivation behind this review. This work is divided in three sections. In the first section, we present the basic principle of the thermoelectric effects when the particles transporting the electric charge are electrons, ions, and redox molecules and describe the conceptual differences between the three thermodiffusion phenomena. In the second section, we review the efforts made on developing devices exploiting these three effects and give a thorough understanding of what limits their performance. In the third section, we review the state-of-the-art thermoelectric materials investigated so far and provide a comprehensive understanding of what limits charge and energy transport in each of these classes of materials.

A New Polystyrene–Poly(vinylpyridinium) Ionic Copolymer Dopant for n‐Type All‐Polymer Thermoelectrics with High and Stable Conductivity Relative to the Seebeck Coefficient giving High Power Factor

“…There is no radical peak for pristine PFClTVT solution, while an obvious radical peak was detected in 5 wt% PSpF doped solution that is at the similar magnetic field with N‐DMBI‐doped polymers. [ 28a,35 ] When PSpF fraction increases to 50 and 100 wt%, the EPR intensity is much stronger than 5 wt% PSpF doped solution, and further proves the effective doping by PSpF. The absorption in the region of 1300–1800 nm (near IR, referenced to absorbance at 1200 nm) increases when the doping ratio increases from 5 to 75 wt%, fully as expected, and then decreases when the dopant/polymer ratio is 100 wt%.…”

Synthetic Nuances to Maximize n-Type Organic Electrochemical Transistor and Thermoelectric Performance in Fused Lactam Polymers

“…This thermal gradient causes charge carriers to diffuse away from the heated side of the OTE material ( Figure 1 b), generating a potential difference across the OMIEC channel, known as a thermovoltage, which is measured as the Seebeck coefficient ( S ), the ratio of voltage difference to temperature difference across the material. 33 The performance of thermoelectric devices can be compared using the figure of merit ZT = PF/κ T where T is the temperature and Z combines the power factor (PF = S 2 σ), composed of the Seebeck coefficient, electrical conductivity (σ), and thermal conductivity (κ). 34 This dimensionless figure of merit applies to both n- and p-type materials and highlights the importance of developing improved n-type materials, as the most efficient thermoelectric generators are composed of p- and n-type materials with similar ZT values.…”

Mesogenic polymer composites for temperature-programmable thermoelectric ionogels

“…1,2 Among the possible power sources for intelligent devices, ionic thermoelectrics (iTEs) composed of ionic polymers are emerging as competitive candidates in terms of a high thermovoltage generation compared to traditional organic thermoelectrics due to their potential as so wearable electronics and Seebeck voltages that are large enough to operate low-voltage driving electronics from a small thermal gradient between the environment and iTEs. [3][4][5][6][7][8][9][10][11] The thermoelectric performance of materials is dened using the thermoelectric gure of merit, ZT ¼ S 2 sT k , where S is the Seebeck coefficient, s is the carrier conductivity, T is the absolute temperature, and k is the thermal conductivity. 12 Generally, the electric thermoelectric performance of polymers depends on the power factor (PF ¼ S 2 s) due to their intrinsically low thermal conductivity.…”