Synthesis and Characterization of Photo/thermo Cross-linkable Self-healing Polymers and Fluorine-functionalized Graphene Oxide/Nafion Composite Membrane for Redox Flow Battery

Abstract

In this report, synthesis and characterization of photo/thermo cross-linkable self-healing polymers and fluorine-functionalized graphene oxide/Nafion composite membrane for redox flow battery. Firstly, methacrylate derivative having photo cross-linkable cinnamate functional group (PCEMA) was synthesized via free radical polymerization. The reversible cross-linking reaction of functional group of PCEMA by changing the wavelength of irradiated UV was confirmed. And the self-healing property at over its glass transition temperature was investigated by monitoring the self-healing property of synthesized methacrylate derivatives with similar structure and different glass transition temperature. Synthesized polymers showed self-healing property over its glass transition temperature by chain entanglement without any chemical reaction. Through this, self-healing polymer with surface hardness control was synthesized and characterized successfully. Secondly, methacrylate derivatives with thermally cross-linkable furan functionality were synthesized by free radical polymerization. And the self-healing polymeric system with enhanced mechanical property was prepared using Diels-Alder reaction with synthesized polymers and maleimide cross-linker. The reactivity of Diels-Alder reaction of furan functionality of polymers were intentionally varied with electron density to investigate its influence to the self-healing property. By increasing the electron density of furan functionality, Diels-Alder reaction with maleimide cross-linker was increased. Through this, it is confirmed that the self-healing property was affected by the reactivity of the healing-inducing functionality. Finally, fluoroalkyl-functionalized graphene oxide (FGO)/Nafion composite membrane was prepared to enhance the performance of Nafion membrane in redox flow battery application. Although composite membrane showed low water uptake and proton conductivity due to the hydrophobicity of introduced fluorine, its dimensional stability was increased and vanadium ion permeability was decreased due to GO. Also, the overall RFB cell performance was increased result from the narrow and fine hydrophilic channel formation of membrane due to the enhanced compatibility with filler and Nafion.