Functional Hydrogel-Based Flexible Thermoelectric Generators: Principles, Mechanism, and Emerging Applications

Area of Science:

• Energy harvesting technologies
• Materials science
• Sustainable energy

Background:

• Thermoelectric generators (TEGs) are devices that convert heat gradients into electrical energy.
• Hydrogel-based TEGs represent a novel, sustainable energy harvesting technology.
• These devices utilize linked ionic, electronic, and redox processes for energy conversion.

Purpose of the Study:

• To review recent developments in hydrogel-based thermoelectric generators (TEGs).
• To investigate the fundamental transport processes enabling thermoelectric conversion in hydrogels.
• To identify challenges and assess methods for improving TEG efficiency.

Main Methods:

• Review of existing literature on hydrogel-based thermoelectric generators.
• Analysis of ionic Seebeck coefficients, thermal and ionic conductivities, and mechanical properties.
• Investigation of transport mechanisms including ionic thermodiffusion and thermoelectric ion-electron coupling.

Main Results:

• Hydrogel-based TEGs exhibit high ionic Seebeck coefficients (10-40 mV K⁻¹).
• They possess modest thermal conductivities (~0.3-0.6 W/m·K) and tunable ionic conductivities (10⁻³-10⁻¹ S cm⁻¹).
• Gels are soft and highly elastic, suitable for flexible applications.

Conclusions:

• Hydrogel-based TEGs show promise for applications like wearable power sources and waste heat recovery.
• Bottlenecks include low output power under minor gradients, requiring further research for efficiency improvements.
• Further research is needed to transition these devices from laboratory settings to practical, sustainable energy solutions.