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Membranes (Basel). 2017 Jun 6;7(2). pii: E29. doi: 10.3390/membranes7020029.

Influence of Membrane Equivalent Weight and Reinforcement on Ionic Species Crossover in All-Vanadium Redox Flow Batteries.

Author information

1
Electrochemical Energy Storage and Conversion Laboratory, Department of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee, Knoxville, TN 37996, USA. yashrafg@utk.edu.
2
Electrochemical Energy Storage and Conversion Laboratory, Department of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee, Knoxville, TN 37996, USA. daaron@utk.edu.
3
Electrochemical Energy Storage and Conversion Laboratory, Department of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee, Knoxville, TN 37996, USA. mmench@utk.edu.
4
Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. mmench@utk.edu.

Abstract

One of the major sources of lost capacity in all-vanadium redox flow batteries (VRFBs) is the undesired transport (usually called crossover) of water and vanadium ions through the ion-exchange membrane. In this work, an experimental assessment of the impact of ion-exchange membrane properties on vanadium ion crossover and capacity decay of VRFBs has been performed. Two types of cationic membranes (non-reinforced and reinforced) with three equivalent weights of 800, 950 and 1100 g·mol-1 were investigated via a series of in situ performance and capacity decay tests along with ex situ vanadium crossover measurement and membrane characterization. For non-reinforced membranes, increasing the equivalent weight (EW) from 950 to 1100 g·mol-1 decreases the V(IV) permeability by ~30%, but increases the area-specific resistance (ASR) by ~16%. This increase in ASR and decrease in V(IV) permeability was accompanied by increased through-plane membrane swelling. Comparing the non-reinforced with reinforced membranes, membrane reinforcement increases ASR, but V(IV) permeability decreases. It was also shown that there exists a monotonic correlation between the discharge capacity decay over long-term cycling and V(IV) permeability values. Thus, V(IV) permeability is considered a representative diagnostic for assessing the overall performance of a particular ion-exchange membrane with respect to capacity fade in a VRFB.

KEYWORDS:

UV-Vis spectroscopy; conductivity; crossover; equivalent weight; reinforcement; swelling; vanadium redox flow battery

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