Facile preparation of stretchable and self-healable conductive hydrogels based on sodium alginate/polypyrrole nanofibers for use in flexible supercapacitor and strain sensors

A series of multifunctional conductive hydrogels (denoted as SA-B-DAPPy) is developed by combining sodium alginate (SA) and dopamine functionalized polypyrrole (DAPPy) nanofibers with borax as a cross-linking agent. By modulation of the DAPPy weight ratio to 3.5 wt%, the conductivity of the hydrogel can reach a high value of 1.33 ± 0.012 S/m. Both borate interactions and hydrogen bonds within hydrogel frameworks can account for the satisfactory stretchability (more than 800%) and instantaneous self-healing ability. More significantly, the SA-B-DAPPy hydorgels can be easily fabricated as electrode component in the symmetric supercapacitor with SA-B-DAPPy//SA-B//SA-B-DAPPy configuration. Due to the self-healing of the electrode/electrolyte interface, the obtained all-in-one device can deliver superior areal specific capacitance of 587 mF/cm2 at current density of 1.0 mA/cm2, high energy density of 52.18 μWh/cm2 at power density of 800 μW/cm2, good capacitance retention of 80% after 2000 cycles, as well as integration characteristics. Furthermore, on account of high conductivity, a thin SA-B-DAPPy hydrogel film can be fabricated into the motion sensor to detect and distinguish various human movements. The sensor exhibits high gauge factor (GF) up to 10.23, and stable, repeatable response signals, which permit supersensitive for monitoring large-scale joints motions and subtle muscle movements.