Supramolecular Interaction-Driven Amorphization of Poly(aryl piperidine) Membranes for Enhanced Proton Conductivity

Abstract

Non-fluorinated polymer membranes offer a commercially feasible solution for redox flow batteries (RFBs), yet their practical applications have been hampered by inherent challenges such as chemical instability and low ionic conductivity. In this study, the development of a series of ether-bond-free poly(aryl piperidine) membranes that address these limitations by introducing enhanced disorder in polymer chain packing through supramolecular interactions with organic acids, is presented. These interactions effectively disrupt densely packed polymer chains, transforming proton-inaccessible crystalline regions into accessible amorphous ones. By eliminating chemically unstable aryl ether bonds and avoiding additional chemical modifications, these membranes exhibit remarkable long-term chemical stability. The presence of abundant interchain gaps further facilitates rapid proton-selective transport. As a result, the engineered membranes demonstrate sustained performance in vanadium RFBs, maintaining stable operation for over 1000 charge/discharge cycles, and achieving an impressive energy efficiency of 80% at a high current density of 280 mA cm⁻². The combination of experimental data and theoretical modeling suggests that the membrane's outstanding performance arises from the interconnected and widely distributed interchain gaps, which exhibit a pore-limiting diameter of ≈8 Å. These findings offer a robust design strategy for developing chemically stable, high-performance non-fluorinated membranes for RFBs and related energy conversion devices.