Nafion/functionalized metal-organic framework composite membrane for vanadium redox flow battery

Although vanadium redox flow batteries hold great promise for energy storage systems, Nafion (being a conventional membrane material) requires improvement in terms of the crossover phenomenon. Herein, a nanoporous metal-organic framework (MOF) is applied as a membrane for vanadium redox flow batteries via addition of the MOF to a Nafion solution to prepare Nafion/MOF composite membranes via casting. Composite membranes are fabricated into a Nafion matrix by introducing small amounts of CAU-10-X (X = -OH, -CH3, -OS1, -OS2), an Al-based MOF synthesized with ligands having hydroxyl, methyl, and a combination of hydroxyl and sulfonic acid functional groups. The membrane physicochemical properties (such as water uptake, swelling ratio, ion exchange capacity, proton conductivity, and electrochemical properties from charge-discharge experiments on a single cell) are compared and evaluated. In 100 charge-discharge cycles of the single cell at a current density of 160 mA cm-2, the composite membrane N/CAU-10-OS1 with 0.6 wt% dispersed MOF and a combination of hydroxyl and sulfonic acid functional groups exhibits capacity retention of 80.34% and energy efficiency of 77.56% at approximately 50 mu m thickness. These values are better those achieved by commercial separation membrane Nafion 115 with 127 mu m thickness tested under identical conditions and the proposed membrane is thus expected to be economically advantageous.

Automated summary

In this study, a nanoporous metal-organic framework was utilized as a membrane material for vanadium redox flow batteries to enhance the performance of conventional Nafion membranes. The addition of small amounts of an Al-based MOF with hydroxyl and sulfonic acid functional groups to the Nafion solution resulted in composite membranes with improved physicochemical properties and electrochemical performance. The proposed composite membrane showed better capacity retention and energy efficiency compared to commercial Nafion membranes, indicating potential economic advantages.