Highly Stretchable, Resilient, Adhesive, and Self‐Healing Ionic Hydrogels for Thermoelectric Application

Abstract Harvesting low‐grade waste heat from the natural environment with thermoelectric materials is considered as a promising solution for the sustainable energy supply for wearable electronic devices. For practical applications, it is desirable to endow the thermoelectric materials with excellent mechanical and self‐healing properties, which remains a great challenge. Herein, the design and characterization of a series of high‐performance ionic hydrogels for soft thermoelectric generator applications are reported. Composed of a physically cross‐linked network of polyacrylic acid (PAA) and polyethylene glycol (PEO) doped with sodium chloride, the resulting PAA‐PEO‐NaCl ionic hydrogels demonstrates impressive mechanical strength (breaking stress >1.3 MPa), stretchability (>1100%), and toughness (up to 7.34 MJ m −3 ). Moreover, the reversible hydrogen bonding interaction and chain entanglement render the ionic hydrogels with excellent mechanical resilience, adhesion properties, and self‐healing properties. At ambient conditions, the electrochemical and thermoelectric performance of the ionic hydrogels can be restored immediately from physical damage such as cutting, and the mechanical healing can be completely restored within 24 h. At the optimized composition, the Seebeck coefficient of the ionic hydrogels can reach 3.26 mV K −1 with a low thermal conductivity of 0.321 W m −1 K −1 . Considering the excellent mechanical properties and thermoelectric performance, it is believed that the ionic hydrogels are widely applicable in ionic thermoelectric capacitors to convert low‐grade heat into electricity for soft electronic devices.