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

Abstract 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.