Wearable Thermoelectric Generator Research Articles

Achieving High Thermoelectric, Stretchable, and Self-Healing Capabilities in Self-Supported PEDOT:PSS/Nafion/Poly(vinyl Alcohol) Composites for Wearable Thermoelectric Power Generators and Sensors

Achieving High Thermoelectric, Stretchable, and Self-Healing Capabilities in Self-Supported PEDOT:PSS/Nafion/Poly(vinyl Alcohol) Composites for Wearable Thermoelectric Power Generators and Sensors

High-performance waterproof flexible thermoelectric generators for self-powered electronics

Flexible and wearable thermoelectric generators (TEG) have emerged as promising energy sources for wearable health-monitoring devices. However, common thermoelectric generators are difficult to be applied to a wide range of application scenarios due to their poor durability, low output power, and susceptibility to human sweat or underwater environments. Here, we propose a waterproof wearable TEG with a gap structure. Through structural optimization and full-coverage elastomer encapsulation, the wearable TEG has a maximum power density of 4.38 mW∙cm−2 at a temperature difference (ΔT) of 30 K and exhibits good stability under aqueous environments, which is capable of supplying power to electronic devices even under submerged conditions. The internal resistance of wearable TEG changes by less than 10 % at 50 % stretch or 900 degrees of torsion, showing good flexibility and mechanical stability. Based on this, we designed an energy harvesting and management system to help wearable TEG collect and utilize energy on demand, and successfully implemented wireless transmission of human skin temperature data for underwater environments and real-time electrocardiograms (ECG) tests for health detection in air environments. This research provides a reliable method for powering wearable electronic devices using thermoelectric generators.

Boosting self-powered wearable thermoelectric generator with solar absorber and radiative cooler

The electrical output of wearable thermoelectric generators (wTEGs) has traditionally been constrained by small temperature differentials when powering microelectronics. In this study, we innovatively combine photothermal and radiative cooling mechanisms within a single wTEGs system, enabling substantial, uninterrupted power generation. Specifically, we designed a multilayer selective solar absorber (m-SSA) composed of flexible dielectric-metal stacks. This absorber demonstrates exceptional solar absorption efficiency of 93 % and significantly low thermal emissivity of 10 %. In practical outdoor conditions, it achieves a temperature increase of up to 108 °C under solar irradiation. Concurrently, we developed a flexible hierarchically porous radiative cooler (HP-RC), which reflects 96 % of solar energy and emits 97 % of thermal energy, achieving a cooling differential of up to 10 °C, even at ambient temperatures of 42 °C. Integration of the m-SSA and HP-RC with wTEGs allows for the simultaneous harvesting of heat from solar, cold space, and earth (robots or human body). This novel energy capture mechanism yielded a notable power density of 198 mW/m² for human body and 52 mW/m2 for steel robots in outdoor wearable applications. This significant advancement promotes the field toward high-performance, integrated green power technologies and holds promise for next-generation wearable self-powered devices.

Experimental and Theoretical Optimization of Wearable Thermoelectric Generators Based on Fill Factor and Leg Geometry

Experimental and Theoretical Optimization of Wearable Thermoelectric Generators Based on Fill Factor and Leg Geometry

Interfacial engineering of flexible Ag2-xSnxS on carbon fabric for enhanced wearable thermoelectric generator

Smart wearable devices are still powered by batteries requiring constant recharging, which is a key challenge faced in wearable technologies. Fabrication of flexible thermoelectric materials that can utilize body heat for wearable applications are an attractive alternative to batteries. Developing a thermoelectric material that is flexible, affordable, and has good performance remains a considerable challenge owing to the constrained thermoelectric efficiency of conducting polymers and the inherent rigidity of inorganic materials. Here, we have used a solvothermal technique to incorporate Ag2-xSnxS into conductive carbon fabric as a flexible thermoelectric material. To further enhance its thermoelectric performance, various concentrations of Ag2-xSnxS are grown on carbon fabric. The monoclinic phase of Ag2S on carbon fabric was verified by XRD analysis. After analyzing the thermoelectric characteristics of Ag1.84Sn0.16S, a maximum power factor of 110 μW/mK2 was observed for the SSS8 sample. This value is four times higher than the percentage of pristine Ag2S-CF. The W-TEG device fabricated using 3 pair modules produced an output voltage ranging from 0.09 to 1.5 mV across a temperature gradient of 3 to 8 K.

Flexible Ag2Se/Ag2S nanocomposite on carbon fabric optimized via interfaced engineered energy filtering effect for a textile based wearable thermoelectric generator

Wearable devices have become increasingly attractive in wearable electronics due to their advantages of environmental friendliness and foldability. The state-of-the-art thermoelectric system depends on inorganic semiconductors that show high electron mobility but lack mechanical stability and thermoelectric performance. Here, We have proposed a solvothermal method to grow Ag2Se/Ag2S nanocomposite on carbon fabric with outstanding properties, demonstrating excellent flexibility. The crystallographic analysis was performed for all samples through XRD and confirmed the orthorhombic Ag2Se and mono-clinic Ag2S. Further, the morphological analysis revealed the enhanced growth on the carbon fabric. We investigated the thermoelectric properties of Ag2Se/Ag2S nanocomposite and achieved a high power factor of 8.1 μW/mK2 which is twice as high as the percentage of the pure Ag2Se. Additionally, thermoelectric legs were fabricated using Ag2Se/Ag2S nanocomposite in a 2-pair module. They produced an output voltage of 0.1 mV to 7.4 mV at a temperature gradient (ΔT) of 3–8 K. This work is a promising approach for obtaining high-performance wearable thermoelectric device.

Flexible and air-stable n-type oleylamine/carbon nanotube hybrid yarns for high-performance wearable thermoelectric generators

Wearable thermoelectric generators (TEGs), envisioned to harness the temperature gradient (ΔT) between the human body and the environment into electricity, hold great promise for powering wearable electronics. However, their practical application has been hampered by the scarcity of flexible n-type thermoelectric (TE) materials boasting both high performance and long-term air stability. Here, we introduce a significant advancement by developing an n-type TE material through immersing carbon nanotube yarn (CNTY) into an oleylamine (OAm)/ethanol solution, followed by drying under atmospheric conditions. The resulting OAm/CNTY exhibits a Seebeck coefficient of -80.48 μV K-1, an electrical conductivity of 1353.18 S cm-1 and a power factor of 876.25 μW m-1 K-2, all while exhibiting exceptional mechanical flexibility. Notably, this hybrid yarn maintains stable n-type behavior even after enduring exposure to air for over 370 days, surpassing previous n-type TE materials based on CNT fibers and CNTY. Leveraging this advancement, we construct a prototype wearable TEG by alternately embroidering pristine p-type CNTY and n-type OAm/CNTY into a polyester spacer fabric, electrically connecting them in series using conductive silver paint. The resulting wearable TEG, featuring with 150 p-n couples, yields an output voltage of 705.94 mV and a maximum output power of 44.34 μW at a ΔT of 40 K. This groundbreaking work opens new avenues for the development of high-performance, air-stable, and flexible n-type TE material, ushering in a new era for wearable TEGs.

Tailored thermoelectric performance of poly(phenylene butadiynylene)s/carbon nanotubes nanocomposites towards wearable thermoelectric generator application

In this study, two conjugated polymers (CPs) featuring poly(phenylene butadiynylene) (PPB) were meticulously synthesized and composited with single-walled carbon nanotubes (SWCNTs) to investigate their thermoelectric properties and fabricate wearable thermoelectric generators (TEGs). These CPs, designated as P1 and P2, were tailored with distinct side chain configurations by incorporating 2-butyloctyloxy and 6-(methyldioctylsilyl)hexyloxy groups, respectively. Notably, P2, characterized by longer side chains with branchpoints farther from the backbone, exhibited planar backbone structure and enhanced solubility, consequently engendering stronger π–π interaction with SWCNTs and facilitating the disperse of SWCNTs through polymer wrapping at bundle surface. Such characteristics therefore contributed to the superior thermoelectric performances of the P2/SWCNTs nanocomposite, yielding a higher power factor (PF) of 216.5 μW m−1 K−2 for the spin-coated film. Furthermore, the corresponding wearable TEGs, which were constructed through spray-coating with 14 legs, resulted in an output power of approximately 49.6 nW under a temperature difference of 25 K, exhibiting successful harvesting of waste heat. Further applications also demonstrated operational efficacy under diverse conditions. These findings not only underscored the significance of side chain engineering in tailoring the thermoelectric properties of CP/SWCNTs nanocomposites but also demonstrated the feasibility of fabricating high-performance wearable thermoelectric devices applicable in versatile contexts.

A new strategy to simultaneously optimize Seebeck coefficient and electrical conductivity of PEDOT:PSS polymer via L-ascorbic acid

PEDOT:PSS flexible thermoelectric materials are promising for future wearable continuous power support, but it remains challenging due to low power factor. Herein, we propose a “one-stone-two-birds” strategy using L-ascorbic acid as the reductant in synthesis of tellurium nanorods and separating agent in in-situ removing PSS chains. L-ascorbic acid reduces Te4+ to Te, supplying inorganic thermoelectric materials with high Seebeck coefficient as fillers to significantly increase the Seebeck coefficient value of PEDOT:PSS. Meanwhile, L-ascorbic acid separates PSS chains from PEDOT chains, resulting in the increase of electrical conductivity at room temperature by ∼360 % due to structure transformation from benzoid structure to the quinoid structure in PEDOT. As a result, the power factor of optimal PEDOT:PSS with Te fillers and L-ascorbic acid treatment is improved significantly by ∼100 times as compared to that of pristine PEDOT:PSS. Finally, a prototype wearable thermoelectric generator was assembled by 18 legs of Te/PEDOT:PSS composites, which demonstrates a high power density of 2.3 μW·cm−2 with good mechanical stability, flexibility and durability. The present study offers a new strategy for rational design of high-performance flexible thermoelectric materials from PEDOT:PSS.

Ultra-low-energy operation of electromagnetic bi-stable actuator under restricted energy supply

During the periodic drug administration for chronic diseases, unexpected battery depletion can be significantly problematic for the patients. While body heat harvesting utilizing the wearable thermoelectric generator (WTEG) shows the significant potential in continuous drug delivery systems (DDSs) by providing ceaseless power source, the power and the voltage output might not be sufficient to drive micropump actuators in such drug delivery systems. The continuous actuating current also imposes an additional challenge in developing efficient and compact voltage boosting circuits. In this paper, we propose an ultra-low-energy operating method of the WTEG-powered electromagnetic micropump system. In combination with our electromagnetic bi-stable actuator (EBA) where the energy demand is discretized, we present (1) the dedicated high-efficient charge pumps (CPs) (2) and the actuating pulse control method to prevent redundant energy waste. The proposed 10-stage charge pump is designed to reduce the conversion loss by utilizing multiple flying-capacitor switching structure, and the 2-stage series–parallel charge pump (SPCP) is fabricated with flexible thin-film super-capacitors (TFSCs) to realize the high boosting performance within compact and wearable features. Applying the proposed control method with the 10-stage CP in our WTEG-powered micropump system, we significantly reduce the charging time per actuation by 88.8% compared to the commercial boosting circuit. Also, the 2-stage SPCP achieves 84.0% reduction in the charging time while utilizing flexible and wearable features, showing a significant potential for self-powered wearable healthcare applications.

A general design framework of flexible thermoelectric devices bridging power requirements for wearable electronics

Wearable thermoelectric generators (WTEGs) promise sustainable power for wearable electronics with various strategies proposed for on-body applications. However, there is still a lack of power-demand-oriented system design that directly provides WTEG configurations tailored to targeted end electronics, resulting in sufficient power only under extreme ambience. To address this, we propose a straightforward, power-demand-oriented design framework for WTEGs that bridges the power requirements of end electronics. As we input the properties of thermoelectric materials, specific operational conditions (temperature and heat transfer coefficient), expected power output and required flexibility, the design framework can directly determine the geometric features of thermoelectric pillars and fill factor. The effectiveness has been widely verified using data from the literature, showing a mean absolute deviation of 7.1 %. This framework shows high working efficiency and significantly shortens the design process, which is the very first ever-reported design tool for WTEGs. As a case, we use the framework and design a skin-conformable thermoelectric textile (TET) with optimal structure configurations and enhanced heat transfer capabilities, achieving a high normalized power density of 4.48 μW cm−2 K−2. As expected, the TET, with a maximum power density of 231 μW cm−2 successfully powered a series of on-body electronics when attached to the forearm at a breezy ambient temperature of ∼283 K. On the other hand, the TET exhibits a cooling effect of 5.73 K. Our work provides a thermal design guide for WTEGs, shedding light on the direct connection between WTEG configurations and end electronics.

Optimization Design and Performance Study of Wearable Thermoelectric Device Using Phase Change Material as Heat Sink.

Wearable thermoelectric generators have great potential to provide power for smart electronic wearable devices and miniature sensors by harnessing the temperature difference between the human body and the environment. However, the Thomson effect, the Joule effect, and heat conduction can cause a decrease in the temperature difference across the thermoelectric generator during operation. In this paper, phase change materials (PCMs) were employed as the heat sink for the thermoelectric generator, and the COMSOL software 6.1 was utilized to simulate and optimize the power generation processes within the heat sink. The results indicated that with a PCM height of 40 mm, phase transition temperature of 293 K, latent heat of 200 kJ/kg, phase transition temperature interval of 5 K, thermal conductivity of 50 W/(m·K), isobaric heat capacity of 2000 J/(Kg·K), density of 1000 kg/m3, and convective heat transfer coefficient of 10 W/(m·K), the device can maintain a temperature difference of 18-10 K for 1930 s when the thermoelectric leg height is 1.6 mm, and 3760 s when the thermoelectric leg height is 2.7 mm. These results demonstrate the correlation between the device's output performance and the dimensions and performance parameters of the PCM heat sink, thereby validating the feasibility of employing the PCM heat sink and the necessity for systematic investigations.

Enhanced Thermoelectric Performance in Flexible Sulfur-Alloyed Ag2Se Thin Films.

Flexible thermoelectric generators can directly convert thermal energy harvested from the human body into electricity. The Ag2Se flexible film, a promising material for wearable thermoelectric generators, normally demonstrates an inferior electrical transport property due to its weakened in-plane mobility. In this study, the in-plane electrical transport properties of flexible Ag2Se films were optimized by alloying with additional sulfur. This optimization is achieved by leveraging the differences in elemental electronegativity and the preferred orientation of the Ag2Se films. The sulfur-alloyed Ag2Se thin film, with a nominal ratio of 3 atom %, can reach a maximum mobility of 1150 cm-2 V-1 s-1 at 300 K. So, the optimized room-temperature power factor increases to 1935 μW m-1 K-2. Furthermore, the Ag2Se film alloyed with 3 atom % sulfur exhibits excellent flexibility even after 1000 bending cycles with a radius of 5 mm, characterized by a relative resistance increment of less than 3%. In addition, the corresponding π-type flexible thermoelectric generator possesses a maximum power density of 51 W m-2 at a temperature difference of 50 K.

Solution-processed MoS2 nanostructures and thermal oxidization on carbon fabric with enhanced thermopower factor for wearable thermoelectric application

Miniaturization of electronic devices has become the new phase of modern technology. Wearable Thermoelectric Generators (WTEG), being flexible, lightweight, self-sustained, and safe are the only replacement for conventional batteries for mobile applications. Molybdenum Disulfide (MoS2), a graphene akin compound having diverse transport behaviour and low thermal conductivity is one of the most preferable candidates for thermoelectric application. However, limited reports are available on MoS2 for Wearable thermoelectric applications. In this study, we have accomplished successful growth of MoS2 nanostructures on conductive carbon fabric via one step hydrothermal method and the effect of thermal oxidation of MoS2 has been studied at various annealing temperature. The structural and elemental analysis confirms the transformation of MoS2 into MoO3. Annealing creates an MoS2/MoO3 interface thus enhancing the carrier mobility resulting in enhancement of power factor (481 nW.m−1K−2) of the sample annealed at 200 °C (M1) by 1.29 times than that of pristine MoS2. The sample possessing high performance has been employed to fabricate a WTEG and its real time output has been measured. The design and operating conditions of the device is studied and optimized to obtain the output open circuit voltage as high as 6.4 mV. This paves a promising route to fabricate self- powered wearable biomedical devices.

How Plasmon Ag Nanoparticles can Enhance the Power Performance of a Thermoelectric Generator.

The development of wearable thermoelectric generators (wTEG) represents a promising strategy to replace batteries and supercapacitors required to supply electrical energy for portable electronic devices. However, the main drawback of wTEGs is that the thermal gradient between the skin and the ambient is minimal, reducing the power output produced by the generator. Therefore, it is necessary to improve the thermal management of wTEG in order to increase its efficiency. This work deals with the preparation of a thermoelectric generator that harnesses the plasmonic heating effect to enhance the thermal gradient of the final device. The thermoelectric layer is created through the in situ polymerization of terthiophene (3T) within a polyurethane matrix, utilizing silver (Ag) (I) and copper (II) perchlorate as oxidants. The plasmonic film, composed of Ag-NP (nanoparticles), is formed via photocatalytic reduction of silver nitrate in the presence of titanium oxide. These layers are then meticulously assembled to yield the hybrid plasmonic/thermoelectric generator.

Controlling Thermoelectric Properties of Laser-Induced Graphene on Polyimide

In the field of wearable thermoelectric generators, graphene-based materials have attracted attention as suitable candidates due to their low material costs and tunable electronic properties. However, their high thermal conductivity poses significant challenges. Low thermal conductivity due to porous structure of the laser-induced graphene, combined with its affordability and scalability, positions it as a promising candidate for thermoelectric applications. In this study, thermoelectric properties of the laser-induced graphene (LIG) on polyimide and their dependence on structural modifications of LIG were investigated. Furthermore, it was shown that increasing the laser scribing power on polyimide results in larger graphene flakes and a higher degree of graphitization. Electrical conductivity measurements indicated an increase with increasing laser power, due to a higher degree of graphitization, which enhances charge carrier mobility. Our findings reveal that LIG exhibits p-type semiconducting behavior, characterized by a positive Seebeck coefficient. It was shown that increasing laser power increased the Seebeck coefficient and electrical conductivity simultaneously, which is attributed to a charge carrier energy filtering effect arising from structures occurred on the graphene flakes. Moreover, the porous structure of LIG contributes to its relatively low thermal conductivity, ranging between 0.6 W/m·K and 0.85 W/m·K, which enhances the thermoelectric performance of LIG. It has been observed that with increasing laser power, the figure of merit for laser-induced graphene can be enhanced by nearly 10 times, which holds promising applications for laser-induced graphene due to the tunability of its thermoelectric performance by changing laser parameters.

Aerosol Doping System for Microscale Seamless p-n Patterning of Carbon Nanotube Films.

Carbon nanotube (CNT) films are extensively researched as a promising material for wearable thermoelectric generators (TEGs) owing to their good flexibility and high thermoelectric conversion ability. Miniaturizing a pair of p- and n-type thermocouples and increasing the number of repeating elements can effectively increase the power of TEGs. However, conventional p-n patterning methods, such as dipping and printing, have a coarse resolution at the submillimeter level, thereby limiting the miniaturization rate. This study developed an aerosol doping system as a fine n-doping method. A dopant aerosol with a <3 μm diameter was formed through ultrasonic nebulization and air separation, while n-doping was achieved by exposing the CNT film to the dopant aerosol. Microscale p-n patterning of 1 μm was achieved through exposure using small-sized aerosols at an exceptionally slow rate of 3 Å/min. This resolution is 100 times higher than those of conventional p-n patterning methods. The developed aerosol doping system for CNTs can also be used on organic semiconductor materials, such as PEDOT/PSS and perovskite materials. Therefore, it has the potential to significantly impact the realization of Internet of Things (IoT) terminals, such as flexible TEGs, transistors, and solar cells.

Carbon Nanotube Yarns Tailored Using Dispersants and Surfactants for Flexible and Wearable Thermoelectric Generators

Carbon Nanotube Yarns Tailored Using Dispersants and Surfactants for Flexible and Wearable Thermoelectric Generators

Dynamic Energy Conversion Performance of Wearable Annular Thermoelectric Generators for Harvesting Human Body Heat

Dynamic Energy Conversion Performance of Wearable Annular Thermoelectric Generators for Harvesting Human Body Heat

Extremely large Seebeck coefficient of gelatin methacryloyl (GelMA)-based thermogalvanic cells by the dual effect of ion-induced crystallization and nanochannel control

The quasi-solid state thermogalvanic cells (TGCs) have been extensively investigated due to their high Seebeck coefficient (S) and suitability for wearable power generation. However, the influence of hydrogel nanostructure on Seebeck coefficient remains underexplored. In this study, biocompatible TGCs based on gelatin methacryloyl (GelMA) are fabricated via a fast-photocrosslinking process. Moreover, guanidium chloride (GdmCl) salts are directly introduced into the TGCs to enhance the Seebeck coefficient via ion-induced crystallization in the p-type FeCN63−/FeCN64− redox system. Small angle X-ray scattering reveals controlled GelMA hydrogel mesh size adjusting the amount of GdmCl, leading to improved intermolecular interactions between the guanidium cations and GelMA polymer. The optimized p-type Seebeck coefficient reaches an unprecedented 21.6 mV K−1, which is the highest thus far reported in the context of the TGC system. Furthermore, a prototype wearable thermoelectric generator (TEG) with an output voltage of 1.6 V under a temperature difference (ΔT) of 9 °C is able to power an LED directly without requiring an additional voltage booster. In brief, the dual effect of ion-induced crystallization and nanochannel control substantially enhances the Seebeck coefficient of the TGC, thereby offering a promising strategy for enhancing the performance of low-grade thermal energy harvesting wearable TEGs.