Highly stretchable double-network gel electrolytes integrated with textile electrodes for wearable thermo-electrochemical cells

Abstract

Thermo-electrochemical cells (TECs) provide a new potential for self-powered devices by converting heat energy into electricity. However, challenges still remain in the fabrication of flexible and tough gel electrolytes and their compatibility with redox actives; otherwise, contact problems exist between electrolytes and electrodes during stretching or twisting. Here, a novel robust and neutral hydrogel with outstanding stretchability was developed via double-network of crosslinked carboxymethyl chitosan and polyacrylamide, which accommodated both n-type (Fe²⁺/Fe³⁺) and p-type ([Fe(CN)₆]^3–/[Fe(CN)₆]^4–) redox couples and maintained stretchability (>300%) and recoverability (95% compression). Moreover, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) textile electrodes with porous structure are integrated into gel electrolytes that avoid contact issues and effectively boost the P_max of n- and p-type thermocell by 76% and 26%, respectively. The optimized thermocell exhibits a quick current density response and is continually fully operational under deformations, which satisfies the working conditions of wearable devices. Multiple thermocells (four pairs) are effectively connected in alternating single n- and p-type cells in series and outputted nearly 74.3 mV at ΔT = 10°C. The wearable device is manufactured into a soft-pack thermocells to successfully harvest human body heat and illuminate an LED, demonstrating the potential of the actual application of the thermocell devices.

Keywords

human body heat / porous textile electrodes / stretchable double-network hydrogel electrolytes / thermo-electrochemical cells / wearable devices

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2024 The Author(s). SusMat published by Sichuan University and John Wiley & Sons Australia, Ltd.