Strong Tough Thermogalvanic Hydrogel Thermocell With Extraordinarily High Thermoelectric Performance

Thermocells can continuously convert heat into electricity, and they are widely used to power wearable electronic devices. However, they have a risk of leakage and poor mechanical properties. Although quasi‐solid ionic thermocells can overcome the issue of electrolyte leakage, the trade‐off between their excellent mechanical properties and high thermopower remains a major challenge. In this study, stretching‐induced crystallization and the thermoelectric effect are combined to propose a high‐strength quasi‐solid stretchable polyvinyl alcohol thermogalvanic thermocell (SPTC) with a large tensile strength of 19 MPa and high thermopower of 6.5 mV K−1. The SPTC exhibits a high stretchability of 1300%, ultrahigh toughness of 163.4 MJ m−3, and high specific output power density of 1969 µW m−2 K−2. These comprehensive properties are superior to those of previously reported quasi‐solid stretchable thermogalvanic thermocells. The use of SPTC‐based systems in wearable devices for energy‐autonomous strain sensors and health monitoring is demonstrated. This can facilitate the rapid implementation of sustainable wearable electronics in the Internet of Things era.