Dual ion-supported poly(vinyl alcohol) (PVA) hydrogel polymer electrolyte for electric double layer capacitor

Poly(vinyl alcohol) (PVA)-sulfuric acid (H2SO4)-lithium trifluoromethanesulfonate (LiOTf) hydrogel polymer electrolytes (HPEs) were prepared by solution casting method. Upon the adulteration of 10 wt.% LiOTf, the ionic conductivity of HPE improves from (9.71 ± 0.04) × 10−3 S cm−1 to (1.06 ± 0.01) × 10−2 S cm−1 at ambient temperature. The glass transition temperature (Tg) of HPE is low compared to pristine PVA, as shown in differential scanning calorimetry (DSC) analysis. The XRD analysis had shown decreased degree of crystallinity upon addition of 10 wt.% of LiOTf. Linear sweep voltammetry (LSV) shows an improvement in potential window from 1.5 to 3.12 V, while transference number proves the ions are the main conduction contributor. An electric double layer capacitor (EDLC) was assembled. The EDLC fabricating using the most conductive HPE exhibits a higher specific capacitance of 18.5 F g−1, as illustrated in CV analysis. The fabricated EDLC demonstrates its specific capacitance of 44 F g−1, energy density of 5.4 Wh kg−1 and power density of 293.8 W kg−1 with above 90 % of coulombic efficiency in GCD analysis.