Surfactant-assisted preparation of all-gel-state flexible supercapacitor with remarkable electrochemical performance based on polyaniline-polyacrylamide/sodium alginate hydrogels

A versatile, highly stretchable, and anti-freezing alginate/polyacrylamide/polyaniline multi-network hydrogel for flexible strain sensors and supercapacitors

Conductive hydrogels have great potential as electrolyte materials for flexible strain sensors and supercapacitors. However, it remains a challenge to develop multifunctional hydrogels with excellent frost resistance, toughness, ionic conductivity, and electrochemical properties using simple methods. Herein, a "chemical-physical-ionic" cross-linked sodium alginate/polyacrylamide/polyaniline (SA/PAM/Ca2+/PANI) multi-network hydrogel was developed by in situ polymerization of aniline monomer within a Ca2+-crosslinked SA/PAM hydrogel network. The SA/PAM/Ca2+/PANI hydrogel shows excellent mechanical properties, (tensile strength of 0.577 MPa at a strain of 1991 %), high toughness (5.52 KJ·m-3), and high ionic conductivity (16.51 S·m-1 at 25 °C and 11.08 S·m-1 at -20 °C). The SA/PAM/Ca2+/PANI hydrogel-based strain sensor exhibited high sensitivity (gauge factor of 3.82 at 60-500 % strain), an extensive detection range (0-2000 %), and excellent frost resistance. The strain sensor can accurately monitor various human motions, as well as electrocardiograph (ECG) signals during both rest and exercise. The supercapacitor assembled with the SA/PAM/Ca2+/PANI hydrogel electrolyte exhibited a high surface capacitance (177.19 mF·cm-2 at 2 mA·cm-2), maximum energy density (21.93 Wh·kg-1), and high power density (3089 W·kg-1). Moreover, it maintained satisfactory electrochemical stability with 77.8 % capacitance retention after 4000 cycles. Therefore, the versatile SA/PAM/Ca2+/PANI hydrogel shows promising potential for applications in flexible wearable electronic devices.

A nanocomposite hydrogel loaded with Ag nanoparticles reduced by aloe vera polysaccharides as an antimicrobial multifunctional sensor

Developing high-performance hydrogels with anti-freeze, and antimicrobial properties is crucial for the practical application of flexible sensors. In this study, we prepared silver nanoparticles (AgNPs) with aloe polysaccharide (AP) as a reducing agent. Then, the AP/AgNPs were added to a system of polyvinyl alcohol and borax crosslinked in water/glycerol to obtain a multifunctional conductive hydrogel. The incorporated AgNPs improved the conductivity (0.39 S/m) and mechanical properties (elongation at break: 732.9 %, fracture strength: 1267.6 kPa) of the hydrogel. In addition, resultant hydrogel exhibited potential for sensing strain, temperature, and humidity. When used as a strain sensor, the hydrogel system exhibited low detection limit (0.1 %), and fast response (0.08 s). The resistance of the hydrogel decreased with an increase in the absorbed moisture content, enabling humidity detection (25-95 %) to monitor breathing status. As a temperature sensor, the hydrogel supported a wide detection range (-50 to +90 °C) and sensitivity (-30-0 °C, temperature coefficient of resistance (TCR) = -5.64 %/°C) to detect changes in the ambient temperature. This study proposes a simple method for manufacturing multifunctional hydrogel sensors, which broadens their application prospects in wearable sensing and electronic products.