# Radiation-Induced Synthesis of Asymmetric Porous PVDF-g-PIL Membranes via β-Cyclodextrin Leaching for Vanadium Redox Flow Battery

## TL;DR

This paper introduces a new method to create porous membranes for vanadium redox flow batteries, improving their performance and efficiency.

## Contribution

The novel use of β-cyclodextrin as a porogen to fabricate asymmetric PVDF-g-PIL membranes for VRFBs is presented.

## Key findings

- The membranes achieved an ionic conductivity of 71.69 mS/cm, a significant improvement over dense membranes.
- Optimal energy efficiency was achieved with intermediate porogen content, balancing conductivity and selectivity.

## Abstract

This study aims to address the limitations of dense polyvinylidene fluoride (PVDF) membranes grafted with vinyl ethyl imidazole tetrafluoroborate, which exhibit low hydrophilicity and ionic conductivity in vanadium redox flow batteries (VRFBs). To improve these properties, water-soluble β-cyclodextrin was introduced as a porogen to fabricate asymmetric porous membranes. The porous structure was controlled by varying the porogen content (10–50 wt%), and the resulting membranes were characterized using FTIR, SEM, TGA, and electrochemical tests. This unique architecture led to a significant enhancement in ionic conductivity (to 71.69 mS/cm, from 6.73 mS/cm for the dense membranes), porosity (up to 40.24%), and water uptake (up to 31.8%), while maintaining robust mechanical strength (tensile strength 14.96 MPa) suitable for VRFB assembly and operation. In single-cell performance tests across a range of current densities, clear trends emerged: Coulombic efficiency (CE) decreased with higher porosity, whereas voltage efficiency (VE) followed the opposite trend. Consequently, the optimal energy efficiency (EE) was achieved with the intermediate porogen content, successfully balancing conductivity and selectivity. This work demonstrates a green and scalable approach to developing high-performance porous membranes for VRFB applications.