Journal article
Species transport mechanisms governing capacity loss in vanadium flow batteries: Comparing Nafion® and sulfonated Radel membranes
Electrochimica acta, v 98, pp 66-74
30 May 2013
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Abstract
• Species transport mechanisms are investigated in Nafion® and s-Radel for VRFBs.
• Unlike diffusion in Nafion®, crossover in s-Radel is dominated by convection.
• In particular, electro-osmotic convection is the dominant mode in s-Radel.
• Change in direction of convection causes a lower crossover in s-Radel.
• Hydraulic and electrokinetic permeability are as important as vanadium permeability.
In this study, a 2-D, transient vanadium redox flow battery (VRFB) model was used to investigate and compare the ion transport mechanisms responsible for vanadium crossover in Nafion® 117 and sulfonated Radel (s-Radel) membranes. Specifically, the model was used to distinguish the relative contribution of diffusion, migration, osmotic and electro-osmotic convection to the net vanadium crossover in Nafion® and s-Radel. Model simulations indicate that diffusion is the dominant mode of vanadium transport in Nafion®, whereas convection dominates the vanadium transport through s-Radel due to the lower vanadium permeability, and thus diffusivity of s-Radel. Among the convective transport modes, electro-osmotic convection (i.e., electro-osmotic drag) is found to govern the species crossover in s-Radel due to its higher fixed acid concentration and corresponding free ions in the membrane. Simulations also show that vanadium crossover in s-Radel changes direction during charge and discharge due to the change in the direction of electro-osmotic convection. This reversal in the direction of crossover during charge and discharge is found to result in significantly lower “net” crossover for s-Radel when compared to Nafion®. Comparison of these two membranes also provides guidance for minimizing crossover in VRFB systems and underscores the importance of measuring the hydraulic and the electro-kinetic permeability of a membrane in addition to vanadium diffusion characteristics, when evaluating new membranes for VRFB applications.
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Details
- Title
- Species transport mechanisms governing capacity loss in vanadium flow batteries: Comparing Nafion® and sulfonated Radel membranes
- Creators
- Ertan Agar - Drexel UniversityK.W. Knehr - Drexel UniversityD. Chen - Pennsylvania State UniversityM.A. Hickner - Pennsylvania State UniversityE.C. Kumbur - Drexel University, Mechanical Engineering and Mechanics
- Publication Details
- Electrochimica acta, v 98, pp 66-74
- Publisher
- Elsevier
- Number of pages
- 9
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Mechanical Engineering and Mechanics
- Web of Science ID
- WOS:000320092000009
- Scopus ID
- 2-s2.0-84875398465
- Other Identifier
- 991019168571304721
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- Collaboration types
- Domestic collaboration
- Web of Science research areas
- Electrochemistry