(681a) Flexible and Sub-Zero Temperature Functioning Porous Hydrogel Supercapacitor Modified By Chemical Crosslinking

For practical applications such as vehicles, the new-generation flexible supercapacitors are demanding to acquire anti-freezing mechanical properties along with high ionic conductivities at low temperatures. It basically means that the gel electrolyte requires to efficiently work at sub-zero temperature and resist flexibility loss in cold weather. Among all the polymer matrices for gel polymer electrolytes (GPE), polyvinyl alcohol (PVA) has been widely investigated due to its low cost, non-toxic, electrical chemical inertness, and chemical stability. Herein, the flexible supercapacitors are created by integrating chemically crosslinked polyvinyl alcohol (PVA) hydrogel electrolytes modified by polyethylene glycol (PEG) to partially replace the water content of the hydrogel and prevent freezing. The hydrogel electrolyte is taking advantage of the heat crosslinking reaction of PVA and PEG with glutaraldehyde (GA), where the hydroxyl groups (-OH) of PVA and PEG bond with aldehyde groups (-CHO) of GA and create acetal or hemiacetal in phosphoric acid solution. The hydrogel also has graphene oxide (GO) content as an enhancement factor for ionic conductivity and capacitance treated in a freeze-drying process to increase the gel porosity and reduce the water content of the gel. The graphene materials’ highly open structure has the capability to enhance the internal structure of the gel by tunable porous channels allowing electrolytes access to the surface of porous frameworks. With freeze-drying at -60 the electrolyte acquired highly distributed micro porosity with a high specific surface area, extremely low densities, and high ion conductivity. Having a matrix made of chemically crosslinked PVA and PEG and enhanced by GO opens new windows in electrolyte properties. The hydrogel has high mechanical strength, and the supercapacitor made of it can perform in very low temperatures until -15 and maintain fast charge-carrier transportation. The device shows a large specific capacitance at the current density of 0.2 mA cm². The supercapacitor performs with excellent energy density and power density.