In situ long-term membrane performance evaluation of hydrogen-bromine flow batteries

Yohanes Antonius Hugo a, b, Wiebrand Kout b, Kitty Nijmeijer a, c, *, Zandrie Borneman a, c
a Membrane Materials and Processes, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, PO Box 513, 5600MB Eindhoven, the Netherlands
b Elestor B.V., 6827 AV Arnhem, the Netherlands
c Dutch Institute for Fundamental Energy Research (DIFFER), P.O. Box 6336, 5600 HH Eindhoven, the Netherlands
⁎ Corresponding author. E-mail address: (K. Nijmeijer).

Because of the impracticality of long life time testing of hydrogen bromine flow batteries (HBFBs) under real, cyclic operating conditions, we utilized a high-frequency cycling load accelerated lifetime test (ALT) to evaluate the membrane electrode assembly performance in HBFBs. Four different membrane chemistries were tested to assesstherelativelong-termperformanceanddurabilityofthecorrespondingHBFBsandtounderstand themain long-term failure mechanism in HBFB technology. The high-frequency cycling load ALT is a highly valuable method to assess long-term HBFB (components) stability and to understand the degradation/failure mechanism. The results showed that the utilization of long side chain perfluorosulfonic acid (LSC PFSA, i.e. Nafion®) membranes result in stable HBFB operation until a sudden cell failure at the end of the cycle life. The use of a more selective (lower bromine species crossover) reinforced LSC PFSA membrane results in approx. five times longer life times. In contrast, the use of a grafted polyvinylidene fluoride (SPVDF) membrane results in a slow incremental performance decrease (or area resistance increase) during the ALT and, again, a sudden cell failure at the end of the cycle life. After the ALT, the LSC PFSA membrane still shows high chemical stability. On the other hand, the grafted SPVDF and SPE membranes show clear membrane degradation visible as a strong decrease in IEC and an increase in ohmic AR. Gradual Pt catalyst degradation-dissolution, that results in insufficient Pt catalyst loading and subsequently low hydrogen reaction kinetics, is the main failure mechanism of the HBFBs. The membrane bromine species crossover rate is directly related to the rate of Pt catalyst degradation-dissolution and scales almost linearly with the celltotal ampere-hours. Aslong as thecatalyst loading issufficientanddoes not reacha minimumvalue,this observed Pt degradation-dissolution rate does not significantly impact the cell performance.