High-Thermopower Thermogalvanic Ionic Hydrogel for Efficient Low-Grade Heat Energy Harvesting in Electronic Devices

Energy is fundamental to human survival and development and also serves as a crucial driving force for sustainable economic growth. Due to the limited efficiency of energy conversion, electronic devices operating at high loads generate substantial amounts of low-grade waste heat. Recycling and reusing of this waste heat can lead to significant energy savings. The present thermoelectric materials typically exhibit low thermopower (or Seebeck coefficient), making it challenging to efficiently recover low-grade waste heat. This study rapidly fabricated polyacrylamide hydrogels via aqueous polymerization and then introduced the Fe(CN)63–/4– redox couple and guanidine hydrochloride through solvent exchange to produce the thermogalvanic ionic hydrogel (TGIH). Subsequently, the water retention and mechanical properties of TGIH were enhanced by introducing the natural moisturizing factor sodium pyrrolidone carboxylate. The TGIH exhibited a high Seebeck coefficient of 5.49 mV/K, a high specific power density of 1213.29 μW/m2·K2, a high water retention rate of 62.7%, a great tensile fracture rate of 523.65%, and a toughness of 0.167 MJ/m3. In addition, an application case is carried on using smartphones; this work demonstrated the TGIH’s capability to efficiently dissipate heat from electronic devices while simultaneously recovering low-grade waste heat. The TGIH can promote the recovery and utilization of low-grade thermal energy and holds significant application potential in sustainable wearable electronics.