Electrode-dependent thermoelectric effect in ionic hydrogel fiber for self-powered sensing and low-grade heat harvesting

Abstract

Ionic thermoelectric materials show great significance for wearable energy devices, owing to the capability of the conversion between thermal and electrical energy. The two-dimensional massive structure which is difficult to integrate with fabrics of ionic thermoelectric materials, however, prevent them from realizing their full potential when employed in wearable electronics. In this work, ionic thermoelectric 1D PAM/LiTFSI4 hydrogel fibers with high aspect ratio, inherent flexibility, conductivity, anti-freezing, self-adhesion and self-healing properties are constructed by free radical polymerization technology based on a template strategy, which contains a PAM polymer matrix and an LiTFSI conductive material. Based on thermal diffusion, owing to the ion size difference, the covalent cross-linked polymer network and the electrode-dependent effect promote rapid transport of the cations and boost ion concentration difference, resulting in a huge ionic Seebeck coefficient of 19.02 mV K−1. Meanwhile, embedding hydrogel fibers into the woven textile demonstrates a promising thermoelectric wristband with desirable human heat collection and electrical output capabilities. What’s more, thanks to the introduction of LiTFSI, the microstructure and molecular network system of hydrogel fibers are reshaped, which significantly improved the ionic conductivity of hydrogel fiber, and endowed them with anti-freezing, self-adhesion and self-healing properties. The PAM/LiTFSI4 hydrogel fiber also has excellent strain and temperature sensing properties, which enable a variety of human signal monitoring. Besides, the hydrogel fiber-based sensor can realize self-powered sensing by generating a thermovoltage. Thus, combining the merits of one-dimensional structure, superior thermoelectric performances, sensing at low temperature, excellent adhesion, self-healing and anti-freezing properties together, believing that the PAM/LiTFSI4 hydrogel fiber will render new numerous in human signal monitoring and low-grade heat harvesting applications like wearable electronics and wearable energy supply devices.