Gel polymer electrolytes (GPEs) are promising candidates for highly efficient flexible electrochemical energy storage devices as they reduce leakage and size of the device as well as improving versatility with varied choice of solvents, polymers, and ions. However, the electrochemical mechanisms governing supercapacitive charge storage using a varied choice of polymers and cations (PVA, PEG, PEO-based Na + and K + ) are not systematically evaluated. In this work, the role of GPEs on the charge storage mechanism of a flexible solidstate asymmetric supercapacitor fabricated using porous carbon as the cathode and SnO 2 −TiO 2 composite flower as the anode with various GPEs, viz., poly(vinyl alcohol), poly(ethylene oxide), poly(ethylene glycol)-NaOH, and KOH, is reported. The composite electrode greatly improves the ion transportation, and the GPEs provide interconnected ion transport channels. The as-fabricated porous carbon/GPE/composite electrode as a flexible asymmetric supercapacitor displays an increased specific capacitance (C S up to ∼42.3 F g −1 ) compared to aqueous electrolytes (up to ∼14.1 F g −1 ). Among the studied GPEs, the poly(ethylene oxide)-NaOH-based GPE showed higher C S than poly(vinyl alcohol)-NaOH and poly(ethylene glycol)-NaOH, as the former offered a high cation response under the charge/discharge process.

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This article reports that extremely thin nanobelts (thickness ~ 10 nm) exhibit pseudocapacitive (PC) charge storage in the asymmetric supercapacitor (ASC) configuration, while show battery-type charge storage in their single electrodes. Two types of nanobelts, viz. NiO-Co 3 O 4 hybrid and spinal-type NiCo 2 O 4 , developed by electrospinning technique are used in this work. The charge storage behaviour of the nanobelts is benchmarked against their binary metal oxide nanowires, i.e., NiO and Co 3 O 4 , as well as a hybrid of similar chemistry, CuO-Co 3 O 4. The nanobelts have thickness of ~ 10 nm and width ~ 200 nm, whereas the nanowires have diameter of ~ 100 nm. Clear differences in charge storage behaviours are observed in NiO-Co 3 O 4 hybrid nanobelts based ASCs compared to those fabricated using the other materials-the former showed capacitive behaviour whereas the others revealed battery-type discharge behaviour. Origin of pseudocapacitance in nanobelts based ASCs is shown to arise from their nanobelts morphology with thickness less than typical electron diffusion lengths (~ 20 nm). Among all the five type of devices fabricated, the NiO-Co 3 O 4 hybrid ASCs exhibited the highest specific energy, specific power and cycling stability.

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