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.

Exploring the Mechanism, Advancements, and Application of Thermogalvanic Effect in Hydrogels

“…prepared a PAA‐PEO‐NaCl ionic hydrogel by cross‐linking PAA and polyethylene glycol (PEO) and incorporating sodium chloride as a doping agent. [ 66 ] This ionic hydrogel surpasses in mechanical strength with a fracture stress exceeding 1.3 MPa, tensile strength surpassing 1100%, and a remarkable toughness of up to 7.34 MJ·m −3 . After optimizing its composition, this hydrogel also demonstrates an impressive Seebeck coefficient of 3.26 mV·K −1 and exhibits low thermal conductivity of 0.321 W·m −1 ·K −1 .…”

“…[ 79 ] Reproduced from ref. 66 with permission from AIP Publishing, copyright 2019. (c) Schematic diagram and photographs of the stretchable TEG using origami‐like folding deformation.…”

Hyper strength, high sensitivity integrated wearable signal sensor based on non-covalent interaction of an ionic liquid and bacterial cellulose for human behavior monitoring

“…Ion sensing hydrogels have 3D networks that provide ideal channels for ion migration, resulting in exceptional electrical conductivity, mechanical properties, and biocompatibility. 15,16 In contrast to conventional conductive materials, these solid flexible ion sensors not only exhibit a remarkable level of stretchability and sensitivity akin to human tissue but also maintain stable sensing performance even under substantial deformations. This unique combination of qualities positions them as preferred materials for wearable devices.…”

Strain-Temperature Dual Sensor Based on Deep Learning Strategy for Human–Computer Interaction Systems

“…We propose a method utilizing Fe 2+ /Fe 3+ redox pairs through a freeze–thaw-immersion process to produce TE hydrogels. This method optimizes the hydrogel’s performance by controlling the aggregation of polymer chains via the Hofmeister effect, resulting in a sensor with exceptional toughness and responsiveness to both strain and temperature. , Integration with robotic systems and optimization using deep learning networks enhance the sensor’s ability to monitor human-body motion, detect robotic hand gestures, issue temperature alerts, and facilitate other human–machine interactions.…”