Vanadium-encased zeolite based mixed matrix membrane for high-performance all-vanadium redox flow battery

Abstract

Achieving high proton selectivity over vanadium ions is crucial for ensuring a long calendar life of vanadium redox flow batteries (VRFBs). Conventional perfluorinated and hydrocarbon-based membranes often struggle to prevent vanadium ion crossover, which compromises VRFB performance. This study highlights the modification of ZSM-5 (40) Na⁺ zeolites with vanadium ions to leverage Donnan exclusion in a galvanostatic charge/discharge process. The membranes were prepared by physically blending the modified zeolite with sulfonated poly(ether ether ketone) (SPEEK). The developed membranes displayed excellent oxidative stability in 2 M H₂SO₄ containing 1.5 M VO₂⁺ ions, along with enhanced electrochemical performance. In single-cell VRFB testing, the membrane with the highest proton conductivity, SPEEK-ZSM 40 VO₂⁺, achieved an average coulombic efficiency of 98.0% and an energy efficiency of 80.37% over 200 continuous charge/discharge cycles at a current density of 80 mA cm⁻². Additionally, it demonstrated a capacity retention of 54% after 100 charge–discharge cycles. Furthermore, polarization curve analysis and self-discharge experiments demonstrated a peak power density of 330.45 mW cm⁻² higher and a 1.3-fold slower self-discharge rate compared to the state-of-the-art Nafion-117® membrane under identical conditions. These findings emphasize the potential of zeolite-based mixed matrix membranes, utilizing Donnan exclusion, as a promising approach for enhancing the efficiency, durability, and operational stability of VRFBs.