Thermoelectric hydrogels: Strategies for controlled fabrication and performance tuning
Driven by the surging demand for the Internet of Things and flexible electronics, thermoelectric hydrogels have overcome the rigidity and brittleness inherent to conventional inorganic thermoelectric materials. Leveraging unique advantages such as high flexibility, tissue-like mechanical properties, and tunable ionic conductivity, they exhibit broad application prospects. However, the unique composite architecture of these materials also poses significant challenges for their rational design and performance optimization. This review summarizes recent advances in thermoelectric hydrogels, beginning with an in-depth analysis of the fundamental working mechanisms, including the Seebeck effect, thermogalvanic effect, and thermodiffusion effect, all governed by electronic or ionic carriers. Key performance parameters are presented, with special focus on the dimensionless figure of merit, while the essential tradeoffs among the Seebeck coefficient, electrical conductivity, and thermal conductivity are thoroughly discussed. Furthermore, the paper highlights controllable fabrication strategies for thermoelectric hydrogels, including polymer network design and incorporation of functional fillers, and provides performance optimization approaches based on electronic, ionic, and hybrid thermoelectric gels. Representative applications in energy harvesting, human–machine interaction, and biomedical monitoring are reviewed to illustrate real-world implementation prospects.