Advanced Wearable Thermocells for Body Heat Harvesting

Abstract

Thermoelectrochemical cells (thermocells) designed for harvesting human body heat can provide constant power output for wearable electronics, supplementing state‐of‐the‐art flexible power storage and conversion solutions. However, a systematic investigation into the optimization of wearable thermocells is lacking, especially with regard to device design, n‐type electrolytes, and electrode/electrolyte integration. Here, a n‐type gel electrolyte: polyvinyl alcohol‐FeCl2/3 with outstanding flexibility and elasticity and exceptional electrolyte/electrode integration into a 3D porous poly(3,4‐ethylenedioxythiophene)/polystyrenesulfonate (PEDOT/PSS) electrode, is produced via an in situ chemical crosslinking method. The integrated n‐type cell shows excellent seebeck coefficients (0.85 mV K−1) and output current density (1.74 A m−2 K−1) that are comparable with an optimized p‐type cell consisting of a carboxymethylcellulose‐K3/4Fe(CN)6 electrolyte with a 3D PEDOT/PSS‐edge functionalized graphene/carbon nanotube electrode (−1.22 mV K−1 and 1.85 A m−2 K−1). The equivalent performance of the n‐type and p‐type cells enables the effective series connection of up to 18 pairs of p–n cells that combines to give an output voltage of 0.34 V (∆T = 10 K). This in‐series device is fabricated into a proof‐of‐concept watch strap, which can harvest body heat, charge supercapacitor (up to 470 mF) as well as illuminate a green light emitting diode, demonstrating the practical applications.

Stretchable and Freeze‐Tolerant Organohydrogel Thermocells with Enhanced Thermoelectric Performance Continually Working at Subzero Temperatures

“…In summary, we design an intrinsically stretchable and eco-friendly organohydrogel thermocell with a synergistic chaotropic effect to address the challenges encountered by power supplies that require wearability, flexibility, and continuous working mode at extremely low temperatures. By disturbing strong hydrogen bonds via the chaotropic effect, the [9,14,31,[39][40][41] h) Comparison of Young's modulus and elongation-at-break ratio. [9,14,31] i) Comparison of thermopower and conductivity.…”

“…In comparison to intrinsically soft thermoelectric materials, [9,14,31,[39][40][41] our anti-freezing organohydrogel thermocell shows extraordinary versatility in terms of large stretchability, mechanical robustness, comparable conductivity, impressive thermopower, high power density, and extremely wide working temperature range (Figure 4g-i and Tables S1-S3, Supporting Information). In particular, conventional aqueous solutions and hydrogels freeze and become brittle at subzero temperatures because water crystalizes with the formation of strong hydrogen bonds.…”

Operando MRI for quantitative mapping of temperature and redox species concentrations in thermo-electrochemical cells

“…Thermocells have many advantageous features such as no moving parts or potentially deleterious effects such as plating, stripping, interphase formation or intercalation processes, which will be beneficial for longevity, and they utilise much lower cost materials than traditional semi-conductor based thermoelectrics, making them promising for large scale, low cost applications. Recently, significant progress has been made in developing wearable thermocells to harvest body heat [5][6][7], as well as in developing new thermocell designs that incorporate separators or membranes [8], material phase transitions [9,10], crystallisation processes [11], and improved electrode [12] and electrolyte [13][14][15] materials to boost their Seebeck coefficient and efficiency.…”

Potentially Wearable Thermo‐Electrochemical Cells for Body Heat Harvesting: From Mechanism, Materials, Strategies to Applications

“…c) Schematic and d) photos of the flexible watch-strap shaped p-n thermocell for body-heat harvesting. c,d) Reproduced with permission [82]. Copyright 2020, Wiley-VCH.…”

“…b) Schematic illustration and SEM images of laser-etched PEDOT/PSS-EFG/CNT and PEDOT/PSS film electrodes. Reproduced with permission [82]. Copyright 2020, Wiley-VCH.…”