Polyacrylamide-Lithium Chloride-MXene Based Conductive Hydrogel as Stretchable Strain Sensor and Triboelectric Nanogenerator

In recent years, hydrogels have exhibited attractive applications in electronic skin, wearable sensors, and energy harvesters owing to their flexibility, stretchability, conductivity, and biocompatibility. In this work, we present a conductive and stretchable hydrogel by combining chemically cross-linked polyacrylamide (PAM) as the primary reagent, lithium chloride (LiCl) as the ionic salt, and MXene as a highly electronegative two-dimensional conductive nanocomposite. The mechanical properties of the hydrogel, including stretchability and compressibility, are improved by tuning the volume of MXene during preparation of the hydrogel. A soft and stretchable wearable sensor is then fabricated by encapsulating the PAM-LiCl-MXene (PLM) hydrogel with two self-adhesive poly(ethylene terephthalate) (PET) films. The sensor offers a high fracture elongation of 1215%, excellent fracture strength of 230 KPa, high sensitivity (GF = 9.6), and high response stability (1000 loading–unloading cycles), enabling the detection of human motions with high durability and reproducibility. In addition to its application as wearable sensors, the PLM hydrogel is utilized to fabricate an energy harvester with a high open circuit voltage (VOC) of 180 V and a high short circuit current (Isc) of 17.2 μA. This hydrogel's ability to both sense strain and harvest energy makes it as an excellent candidate for a combined wearable sensor and energy harvester.