High-performance hydrogel electrolytes with eminent toughness, high conductivity and anti-freezing properties have extensive applications in wearable devices or implantable sensors. However, it is still difficult to integrate excellent mechanical properties and high conductivity into one hydrogel sample simultaneously. This work introduced NaCl into a poly(vinyl alcohol)/poly(acrylic amide) (PVA/PAM) double network hydrogel to prepare PVA/PAM/NaCl supramolecular hydrogel electrolytes via a one-pot method. NaCl introduces physical entanglement into the PVA/PAM/NaCl hydrogel electrolytes and provides a dense and wrinkled three dimensional (3D) network nanostructure. The PVA/PAM/NaCl hydrogel electrolytes not only showed excellent mechanical properties (tensile strength up to 477 kPa, elongation at break to 1072% and a fracture energy of 2.484 MJ m⁻³), but also had high conductivity (up to 6.23 S m⁻¹). A strain sensor based on the PVA/PAM/NaCl hydrogel electrolytes exhibited very high sensitivity (gauge factor = 24.901) with the ability of precise and reliable detection of human motions. Hydrogels also showed excellent anti-freezing properties and maintained excellent mechanical properties and conductivity at −20 °C. Introducing a physically cross-linking network through the effects of a metal salt could promote the performance of the hydrogels. This work provides a new insight into the design of multifunctional materials with applications on electronic skin, wearable devices and biosensors.

The rapid development of human–machine interface technologies is dependent on flexible and wearable soft devices such as sensors and energy storage systems. One of the key factors for these devices is the hydrogel electrolyte. In this work, firstly we constructed an anti-freezing, self-healing, adhesive and tough conductive double network ionic organohydrogel by simultaneously introducing NaCl and glycerol (Gly) into poly(vinyl alcohol)/poly(acrylic amide-acrylic acid) (PVA/PAMAA). Then, based on this organohydrogel, a strain sensor and a flexible all-solid-state supercapacitor were assembled separately and their properties were measured. The fabricated strain sensor showed a highly sensitive response (gauge factor = 8.303) in a broad strain range (from 500 to 1000%), enabling the accurate and reliable detection of various mechanical deformations. Meanwhile, the flexible all-solid-state supercapacitor demonstrated a specific capacitance of 75.75 mF cm⁻², high cycling stability (90.2% retention rate after 5000 cycles) and excellent mechanical stability. Lastly, a self-powered integrated system composed of the strain sensor and flexible all-solid-state supercapacitor was fabricated. The sensor can be driven by the supercapacitor and operate stably in a wide strain range sensing test with low power consumption. More importantly, the self-powered integrated system could be directly attached to the human body to detect human motions, showing its great potential application in wearable devices. This work would enlarge the research and application of high-performance ionic hydrogel electrolytes.

Conductive hydrogels have found large application prospects in the fabrication of flexible multifunctional electronic devices for future-generation wearable human–machine interactions. However, their inferior mechanical strength, low-temperature resistance, and non-recyclability, resulting in the waste of resources, severely hinder their application. Thus, starch bio-based hydrogels have attracted significant attention. Starch is the most abundantly available biodegradable biopolymer. However, starch bio-based hydrogels usually show low toughness, high brittleness and low anti-freezing properties. Thus, to address these issues, herein, glycerol and CaCl₂ were concurrently introduced to a starch/poly(vinyl alcohol) (PVA) hydrogel to improve its mechanical, thermal and conductive properties. The effect of glycerol and CaCl₂ on the crystallinity, mechanical, thermal and conductive properties was revealed by X-ray diffraction, tensile testing, differential scanning calorimetry, and electrochemical impedance spectroscopy. The thermoplasticity and healing properties of the starch/PVA/glycerol/CaCl₂ organohydrogel was also evaluated. Due to the role of glycerol and CaCl₂, the compatibility between starch and PVA improved, and thus the as-prepared organohydrogels showed favorable mechanical flexibility and demonstrated anti-freezing ability and long-term stability at ambient temperature. Besides, the abundant hydrogen bonds formed among PVA, starch, glycerol and water endowed the organohydrogels with high stretchability (>790%) and good thermoplasticity. Finally, based on the starch/PVA/glycerol/CaCl₂ organohydrogel, a flexible all-solid-state supercapacitor and strain sensor were assembled and their performances were measured. The supercapacitor displayed an areal specific capacitance of 107.2 mF cm⁻² at 1 mA cm⁻². Moreover, the strain sensor demonstrated high sensitivity (gauge factor of 3.422) and could be directly attached to the human body to detect motion.