A Comprehensive Review on Hydrogel‐Based TENGs: Materials, Mechanisms, and Future Prospects for Wearable and Energy‐Harvesting Applications

The rapid growth of wearable electronic devices and Internet of Things (IoT) applications creates an urgent need for sustainable, flexible, and self‐powered energy sources that can operate without batteries. Hydrogel‐based triboelectric nanogenerators (H‐TENGs) represent a new and revolutionary class of energy harvesters that address this need. These devices utilize the ionic conductivity, mechanical compliance, biocompatibility, and skin‐like properties of hydrogels to harvest biomechanical energy while providing real‐time, battery‐free sensing capabilities. This review provides a comprehensive examination of H‐TENGs, covering their composition, operating principles, manufacturing approaches, performance metrics, and multidisciplinary applications. To achieve this, this review provides an overview of advanced materials such as dual‐network structures, MXene nanocomposites, self‐healing materials, zwitterionic materials, and antifreezing organohydrogels. Reported power density values range from less than 1 to 10,000 mW m −2 . Additionally, it critically evaluates the key challenges facing H‐TENGs, including dehydration, mechanical fatigue, integration complexity, and sustainability concerns. Finally, this review proposes a roadmap for H‐TENG development from 2035 to 2040, identifying enabling technologies for noninvasive health monitoring, adaptable soft robotics, deployable environmental sensing networks, and washable smart textiles.