Ionic Gels for Low‐Grade Heat Energy Harvesting and Thermal Sensing

Harvesting the low-grade heat energy from the environment and the human body remains an underutilized energy. Ionic thermoelectric (i-TE) gels have garnered significant attention in the fields of energy harvesting and sensing due to their exceptional stretchability, adaptability, ease of large-scale fabrication, and excellent thermoelectric performance. This review aims to provide a comprehensive overview of the recent progress of i-TE gels in application of temperature sensing and low-grade heat energy harvesting. The narration begins with the introduction of the synthetic and natural polymer for i-TE gels. Then, various methods are discussed to enhance the mechanical performance (stretchability, self-healing, and mechanical durability) to satisfy the flexible device based on i-TE gels. Noticeably, this work emphatically summarizes the improvement methods of thermopower for i-TE gels, including the preparation of n-type i-TE gels and the bidirectional modulation of their thermopower. Finally, this work explores the diverse applications of i-TE gels, including low-grade heat harvesting, sensing, human-machine interfaces, and biomedical applications.