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Choi et al. Energy Mater. 2025, 5, 500106 https://dx.doi.org/10.20517/energymater.2025.50 Page 23 of 28

Figure 13. Ionic thermoelectric generators (ITEG). (A) i-TE characterization of the PAA-PEO-SDC ionic hydrogels: output power density
[89]
measured under different external loads. Reproduced with permission . Copyright 2024, Wiley-VCH GmbH; (B) ITEGs with PAM-
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LiCl-based double-network hydrogel. Reproduced with permission . Copyright 2022, American Chemical Society.
shows promise. Nonetheless, achieving long-term hydration while preserving mechanical flexibility remains
a fundamental challenge, necessitating innovative material designs and advanced engineering solutions.
Another major limitation is the inherently low ionic conductivity of hydrogel-based i-TE materials, which
restricts their energy conversion efficiency. To address this issue, hybrid hydrogels incorporating
conductive materials such as carbon nanotubes, graphene, or conductive polymers have been developed .
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These hybrid structures improve the electrical conductivity without compromising the intrinsic flexibility
and ionic mobility of the hydrogel matrix, making them more viable for real-world applications. Mechanical
durability under repeated thermal and mechanical stress, particularly in wearable or dynamic environments,