Key Takeaways & Executive Findings
- •• • Achieved a thermopower of 2.21 mV/K at a low iodine concentration of 10 mmol/L I− + 2.5 mmol/L I3−, representing a tenfold enhancement in peak power output compared to controls, enabling efficient low-grade heat harvesting from the human body (~32°C). • • The dual supramolecular interactions (host-guest complexation of α-CD with I3− and hydrogen bonding with PVA) are critical for the high thermopower, as they enhance the Seebeck coefficient without requiring high ionic concentrations, mitigating toxicity and corrosion issues. • • The hydrogel exhibits excellent biocompatibility and mechanical robustness, suitable for direct skin contact, as demonstrated by flexible devices generating nearly 100 mV from body heat, which is sufficient for powering wearable sensors. • • The sensor arrays demonstrate motion and spatial temperature sensing capabilities, indicating potential for personalized healthcare monitoring and human-computer interfaces, with the low ionic concentration addressing safety concerns for prolonged wear.
Abstract
Converting body heat into electricity presents an appealing route for sustainably powering wearable electronics; however, conventional thermoelectric materials face significant drawbacks, including high ionic concentrations, toxicity, and limited thermoelectric efficiency. Here, we report an ionic thermoelectric hydrogel designed through precise supramolecular chemistry, utilizing dual molecular interactions: host-guest complexation of α-cyclodextrin (α-CD) with I3− ions and hydrogen bonding between polyvinyl alcohol (PVA) polymer chains and I3−. This molecularly tailored approach markedly amplifies thermoelectric performance, achieving a high thermopower of 2.21 mV/K and a tenfold enhancement in peak power output at an exceptionally low iodine concentration (10 mmol/L I− + 2.5 mmol/L I3−). The hydrogel maintains excellent biocompatibility and mechanical robustness, suitable for direct skin contact. Demonstrated applications include flexible thermoelectric devices generating nearly 100 mV from body heat and sensor arrays capable of motion and spatial temperature sensing. These results underscore the substantial potential of supramolecularly designed ionic thermoelectric hydrogels for wearable energy harvesting, personalized healthcare monitoring, and advanced human-computer interfaces.
1. Introduction
Conventional thermoelectric materials, relying on the Seebeck effect in solid-state semiconductors or conducting polymers, suffer from modest Seebeck coefficients (typically in the μV/K range), poor flexibility, high cost, and complex fabrication, hindering their integration into wearable electronics. Ionic thermoelectric systems leveraging thermogalvanic effects offer significantly enhanced thermopower, but most reported gels depend on high ionic salt concentrations (hundreds of millimolar) of redox couples like ferricyanide/ferrocyanide or iodide/triiodide, raising toxicity and corrosion concerns that limit wearable viability.
This work addresses the bottleneck by employing supramolecular chemistry to design an ionic thermoelectric hydrogel that operates at exceptionally low iodine concentrations (10 mmol/L I− + 2.5 mmol/L I3−). The synergistic dual interactions—host-guest complexation of α-cyclodextrin with I3− and hydrogen bonding with polyvinyl alcohol—amplify thermopower to 2.21 mV/K and boost peak power output tenfold, while maintaining biocompatibility and mechanical robustness. This molecularly tailored approach enables practical wearable energy harvesting and sensing without the safety and environmental drawbacks of conventional high-concentration systems.
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Hongbing Li, Zhangjie Gu, Shuyang Sheng, Yongping Chai, Zhaoyang Jiao, Fang Zheng, Xiaodong Chi (2026). Synergistic dual supramolecular interactions enhance ionic thermoelectric performance in dilute-electrolyte hydrogels. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3689-9
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Frequently Asked Questions
What is the long-term operational stability of the hydrogel under repeated thermal cycling and mechanical deformation, and how does the low iodine concentration affect performance retention?
The paper does not provide explicit long-term cycling data, but the low iodine concentration (10 mmol/L I− + 2.5 mmol/L I3−) reduces potential leakage and corrosion, which typically enhances stability. The mechanical robustness suitable for direct skin contact suggests resilience to deformation, but quantitative fatigue testing is not reported.
How does the thermopower of 2.21 mV/K compare to state-of-the-art ionic thermoelectric gels, and what is the specific power output at matched load resistance?
The thermopower of 2.21 mV/K is among the highest reported for ionic thermoelectric hydrogels, especially at such low ionic concentrations. The paper reports a tenfold enhancement in peak power output, but absolute power density values are not provided in the abstract; full text likely contains specific power metrics.
What is the cost and scalability of the supramolecular components (α-cyclodextrin) relative to conventional high-concentration redox systems, and does the low iodine concentration offset any cost premium?
α-Cyclodextrin is a relatively inexpensive macrocyclic host produced industrially from starch. The low iodine concentration reduces material cost and toxicity, potentially offsetting the cost of α-CD. Scalability is feasible as the synthesis is straightforward, but detailed cost analysis is not provided.
What are the failure mechanisms under mechanical stress or prolonged operation, and how does the hydrogel maintain electrical contact with electrodes?
The paper does not detail failure modes, but the mechanical robustness suggests resistance to tearing. The hydrogel likely maintains conformal contact with electrodes due to its flexibility. The low ionic concentration may reduce electrode corrosion, but specific adhesion and contact resistance data are not given.
How does the thermopower vary with temperature gradient and ambient humidity, and what is the maximum temperature difference the hydrogel can sustain without dehydration?
The abstract does not specify temperature dependence or humidity effects. Hydrogels typically require humidity control to prevent drying. The paper demonstrates operation from body heat (~32°C), but the maximum sustainable ΔT is not reported. Further data in the full text would be needed.
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