Preparation and Characterization of PVA hydrogel for energetic applications

The development of flexible devices such as displays, smart garments and health monitors, which represents a booming direction for wearable electronics gives improvement of developing high-quality flexible energy storage systems including supercapacitors (SCs) and batteries. SCs, or electrochemical capacitors, have been attracting attention due to the high-power densities and long cycle life span, while batteries normally exhibit high energy densities with relatively low power densities. A SCs is formed by two collectors and an interlayer. The collectors collect charges and store them, while the interlayer must be a system where charges can pass through easily. However, the traditional energy storage devices made by metals and liquid interlayers are structurally stiff or non-flexible, which hinders them from being used in the flexible electronics. In this thesis, to prepare a flexible SCs we investigate the usage of hydrogels as interlayers. PVA (poly vinyl-alcohol) based hydrogels have been used and different PVA molecular weights hydrogels are compared in their mechanical and electrochemical properties. The PVA molecular weights used are the following: 13000-23000, 31000-50000, 89000-98000 and 1 M H2SO4 has been chosen as electrolyte to increase the ionic conductivity of hydrogel in all the cases. The PVA hydrogel has been obtained using the freezing-unfreezing cycles method. All the hydrogels have been characterized mechanically through the tensile and the compression test, while the electrochemical properties are studied with EIS (Electrochemical Impedance Spectroscopy). PVA 31000-50000 gives the best results to be tested for SCs preparation. A Cellulose/PANI foil has been used as charges collector. Alternatively, we try to optimize the direct connection between the hydrogel and a PANI film (interlayer and collectors) in two different ways: letting the hydrogel absorb aniline and polymerize in situ; creating a polyaniline layer and putting liquid PVA over it.