Smart Functional Hydrogels: Emerging Platforms for Thermal and Electrochemical Energy Harvesting and Conversion Systems

The growing demand for sustainable and high‐efficiency energy technologies has intensified the search for multifunctional and smart functional hydrogels capable of simultaneously harvesting, converting, and storing energy as transformative platforms at the intersection of photovoltaic, thermogalvanic, and electrochemical systems. Smart functional hydrogels offer a unique combination of mechanical flexibility, high ionic conductivity, and self‐healing capabilities within water‐rich three‐dimensional networks, transcending conventional structural functions by integrating energy frameworks where thermal management and energy conversion are effectively coupled. Thermogalvanic hydrogels convert low‐grade thermal energy into electricity while functioning as quasi‐solid electrolytes for supercapacitors. Hydrogel‐based cooling layers in thermophotovoltaic devices also enhance power conversion efficiencies and longevity, while multifunctional coatings facilitate the development of ultrathin, flexible photovoltaic modules for wearable and biomedical electronics. By hybridizing hydrogel chemistry with nanomaterials and redox‐active polymers, recent innovations have led to safe, durable, and conformable energy‐conversion and storage devices. This review explores the material science, operational mechanisms, and cutting‐edge applications of smart functional hydrogels across these interconnected domains, while discussing the challenges and future directions required to realize robust, scalable, and autonomous energy platforms.