Self-healable and redox active hydrogel obtained via incorporation of ferric ion for supercapacitor applications

Poly (vinyl alcohol)/phytic acid (PVA/PA) hydrogels have been identified as self-healable electrolytes. In this work, a novel redox active and self-healable PVA/PA/Fe3+ (PPFe) hydrogel containing dual cross-linking network through the formation of both metal coordination bonds and hydrogen bonds was fabricated via a freezing-thawing method. For the first time to our best knowledge, it was found that the introduction of dynamic Fe3+ coordination bonds into the PPFe hydrogel not only improved its mechanical properties and self-healing ability via re-configuration of various bonds, but also afforded the hydrogel high electrochemical redox activity. Compared with plain PVA/PA hydrogels, the as-fabricated PPFe gel delivered greatly improved mechanical properties, including a tensile stress of 0.618 MPa and tensile strain of 924 %, as well as a strain self-healing efficiency of 72 %. The self-healable and redox active PPFe hydrogel was further utilized to fabricate supercapacitors, where the redox reaction of Fe3+ occurred on polyaniline/carbon nanotubes (PANI/CNTs) electro-active material, resulting in an ultra-high 1526 mF/cm2 at 0.5 mA/cm2, and a remarkable energy density of 0.212 mWh/cm2 at 0.25 mW/cm2, as wells as an excellent cycling stability. Moreover, it could recover its electrochemical performance after the cutting-healing, which would greatly improve the reliability and safety of the energy storage device.