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Choi et al. Energy Mater. 2025, 5, 500106 Energy Materials
DOI: 10.20517/energymater.2025.50

Review Open Access

Perspectives on hydrogel-based ionic

thermoelectrics: from mechanistic insights to
wearable applications of thermo-diffusive ionic

materials

2
1,2
Yoohyeon Choi , Jin Young Kim , Byeong-Cheol Kang 1,* , Heesuk Kim 1,3,*
1
Electronic and Hybrid Materials Research Center, Korea Institute of Science and Technology (KIST), Seoul 02792, Republic of
Korea.
2
Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Republic of Korea.
3
Division of Energy & Environment Technology, KIST School, Korea University of Science and Technology, Seoul 02792, Republic
of Korea.
*Correspondence to: Dr. Byeong-Cheol Kang, Electronic and Hybrid Materials Research Center, Korea Institute of Science and
Technology (KIST), 5, Hwarang-ro 14-gil, Seongbuk-gu, Seoul 02792, Republic of Korea. E-mail: bckang23@kist.re.kr;
Dr. Heesuk Kim, Electronic and Hybrid Materials Research Center, Korea Institute of Science and Technology (KIST), 5,
Hwarang-ro 14-gil, Seongbuk-gu, Seoul 02792, Republic of Korea. E-mail: heesukkim@kist.re.kr
How to cite this article: Choi, Y.; Kim, J. Y.; Kang, B. C.; Kim, H. Perspectives on hydrogel-based ionic thermoelectrics: from
mechanistic insights to wearable applications of thermo-diffusive ionic materials. Energy Mater. 2025, 5, 500106. https://dx.doi.
org/10.20517/energymater.2025.50
Received: 28 Feb 2025 First Decision: 19 Mar 2025 Revised: 2 Apr 2025 Accepted: 9 Apr 2025 Published: 16 May 2025

Academic Editor: Bin Wang Copy Editor: Fangling Lan Production Editor: Fangling Lan

Abstract
Hydrogel-based ionic thermoelectric (i-TE) materials that rely on ion migration driven by thermal gradients have
emerged as promising candidates for efficient low-grade heat harvesting. They offer high Seebeck coefficients,
mechanical flexibility, and biocompatibility, making them especially attractive for wearable electronics and
biomedical applications. Among various i-TE materials, hydrogels are particularly notable due to their unique
structure and ability to modulate ion diffusion via interactions between the polymer network and ionic species.
Despite increasing interest in hydrogel-based i-TE materials, the fundamental mechanisms governing
thermodiffusive ion transport remain poorly understood, especially when compared to the more established
thermo-galvanic processes. Moreover, the unique composite architecture of these materials combining polymer
matrices with diverse ionic components presents significant challenges for rational design and performance
optimization. This review addresses these challenges by systematically analyzing the fundamental mechanisms of
hydrogel-based i-TE materials, with a particular focus on the Soret effect and the roles of polymer networks and

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