Effect of ionic liquid on sustainable PVA-sodium alginate electrolyte membranes for high-performance zinc-ion hybrid supercapacitor

Biodegradable synthetic polymer, poly(vinyl alcohol), PVA and polysaccharide-based blend electrolytes offer high ionic conductivity, good mechanical strength, better electrode-electrolyte contact and wide electrochemical stability window (ESW). In this research, plasticized polymer-biopolymer blend electrolyte (PBBE) membranes based on [PVA-sodium alginate (NaAlg)-zinc triflate] and ionic liquid (IL), [EMIM][TFSI] have been prepared using the solution casting method. The formulated samples were characterized using XRD, FESEM, Infrared (IR) spectroscopy, impedance spectroscopy (EIS), transference number (TN) and linear sweep voltammetry (LSV) measurements. XRD and FESEM results demonstrate that the loading of ionic liquid significantly modifies the crystalline phase and surface morphology of the prepared samples. IR results confirm the interactions between EMIM + /Zn 2+ ions with OH/COO - functional groups of PVA-NaAlg blend. The PBBE membrane loaded with 60 wt.% IL (i.e. PSZnIL#60) has the maximum ionic conductivity of 5.2 × 10 -3 S cm -1 , with TN of 0.99. Loading IL improves the ESW of PBPE membranes significantly. The temperature-dependent ionic conductivity analysis followed Arrhenius-type behavior for all PBBE membranes. A Zn-ion hybrid capacitor (ZIHC) based on PSZnIL#60 delivered a specific capacitance of 306.66-50.70 F g -1 , energy density of 161.96–14.20 Wh kg -1 , and power density of 195–3408 W k g -1 across current densities of 0.1–2.4 A g -1 . The stability test conducted at a current density of 1.2 A g -1 revealed that the device achieved a high coulombic efficiency of 98% and maintained 87% of its initial capacity after 5000 charge–discharge cycles, highlighting its strong potential for energy storage applications. • IR results reveal the interactions of EMIM + /Zn 2+ with OH/COO - of PVA-NaAlg blend • IL acts as a plasticizer, weakening the Zn 2+ –alginate bonds as evidenced by XRD & FESEM • IL loading improves the ESW and PSZnIL#60 membrane has the σ dc = 5.2 × 10 -3 S cm -1 • The ZIHC device exhibits C s = 306.66 F g -1 , E d = 161.96 Wh kg -1 with P d = 195 W kg -1 • ZIHC retained 87% capacity with 98% Coulombic efficiency after 5000 cycles of charge-discharge