A self-powered flexible sensing system based on a super-tough, high ionic conductivity supercapacitor and a rapid self-recovering fully physically crosslinked double network hydrogel

Abstract

Recently, hydrogel flexible sensors have attracted wide attention in the field of wearable electronic devices. However, they need an external solid-state power supply to output stable signals. The huge modulus difference between solid-state power supplies and hydrogel flexible sensors is not conducive to the integration, portability, and application of hydrogel flexible sensors. Therefore, it is necessary to design power supplies with a similar modulus to those of flexible sensors and assemble them with flexible sensors to develop self-powered flexible sensing systems, which is important to facilitate the integration, portability, and application of flexible sensors. In this work, polyvinyl alcohol (PVA), sodium chloride (NaCl), and N-hydroxyethyl acrylamide (HEAA) were used to synthesize a fully physically crosslinked double network hydrogel (PNH DN hydrogel) with excellent mechanical performance (tensile stress/strain of 3.76 MPa/872.15%), high ionic conductivity (1.3 S m⁻¹), and rapid self-recovery (energy dissipation/peak stress recovery efficiency of 57.08%/99.06% after a rest time of 10 min). Based on PNH DN hydrogels, a hydrogel strain sensor and a flexible solid-state supercapacitor were prepared, respectively. The hydrogel strain sensor based on the PNH DN hydrogel showed good sensitivity (gauge factor = 1.74), a wide detection range (0–735%), and a negligible response delay time (0.06 s), which are helpful for timely and reliable detection of various mechanical deformations. Meanwhile, the supercapacitor based on the PNH DN hydrogel exhibited an areal capacitance of 2.9 mF cm⁻², a high cycle stability (areal capacitance retention rate of 85.71% after 2000 galvanostatic charge–discharge cycles at a current density of 0.5 mA cm⁻²), and mechanical stability (cyclic voltammetry curves were almost overlapped under 0°, 45°, 90°, 135°, and 180° bending). Finally, the hydrogel strain sensor and supercapacitor were integrated into a self-powered flexible sensing system, which could stably and effectively detect human motions, such as finger bending, neck bending, and frowning. Overall, this work provides a new idea to improve the integration, portability, and application of hydrogel flexible sensors and can broaden the application of hydrogels in the field of new energy.