Evaluation of perfluorinated sulfonic acid membranes for vanadium redox

Abstract

The performance and cost of the membranes have always been crucial for the utilization of electrochemical energy devices. This article presents the properties and the performance of two commercially available and low-cost perfluorinated sulfonic acid membranes of GN115 and GN212C for vanadium redox flow battery (VRFB) application in comparison with Nafion117 (N117) membrane. The vanadium (IV) permeability of GN115 membrane was found to be close to N117, unlike GN212C membrane which showed 4 times higher vanadium (IV) permeability than N117 under similar conditions. Both GN115 and GN212C membranes showed isotropic conductivity and higher values than N117. The battery test results indicated that the high coulombic efficiency (CE) and high voltage efficiency (VE) followed the vanadium (IV) permeability and proton conductivity trends. Both membranes revealed outstanding stability in long-term charge-discharge testing under various current densities. The energy efficiency was found to be higher than N117 with values of 76.6% and 76.8% for GN115 and GN212C, respectively. The overall results suggest that both lower-cost membranes have a strong potential for VRFB application as the single-cell performance results were close to N117. The high value of proton conductivity of GN212C membrane compensates its vanadium (IV) permeability leaving reasonable battery performance.