Boosting Contact Electrification by Amorphous Polyvinyl Alcohol Endowing Improved Contact Adhesion and Electrochemical Capacitance.

Abstract

Ion conductive hydrogels are relevant components in wearable, biocompatible, and biodegradable electronics. Polyvinyl-alcohol (PVA) homopolymer is often the favored choice for integration into supercapacitors and energy harvesters as in sustainable triboelectric nanogenerators (TENGs). However, to further improve hydrogel-based TENGs, a deeper understanding of the impact of their composition and structure on devices performance is necessary. Here, it is shown how ionic hydrogels based on an amorphous-PVA (a-PVA) allow to fabricate TENGs that outperform the one based on the homopolymer. When used as tribomaterial, the Li-doped a-PVA allows to achieve a twofold higher pressure sensitivity compared to PVA, and to develop a conformable e-skin. When used as an ionic conductor encased in an elastomeric tribomaterial, 100 mW cm^-2 average power is obtained, providing 25% power increase compared to PVA. At the origin of such enhancement is the increased softness, stronger adhesive contact, higher ionic mobility (> 3,5-fold increase), and long-term stability achieved with Li-doped a-PVA. These improvements are attributed to the high density of hydroxyl groups and amorphous structure present in the a-PVA, enabling a strong binding to water molecules. This work discloses novel insights on those parameters allowing to develop easy-processable, stable, and highly conductive hydrogels for integration in conformable, soft, and biocompatible TENGs.