Neutron Radiography Applied to All-Vanadium Redox Flow Batteries for Side Reaction Detection

Redox flow batteries are a technology of interest due to their potential for large-scale energy storage [1]. Recent progress has led to improvements in materials, performance, and stability; however much improvement is still possible. In order to make further progress, these systems must be understood at a more fundamental level. In situ diagnostic techniques provide deeper insight into the underlying mechanisms governing their operation and limitations. Such tools have proven useful in enhancing understanding of other electrochemical cells. One diagnostic tool that has been implemented for fuel cells is neutron radiography [e.g. 2,3].

Neutron imaging of fuel cells involves the detection of liquid water in a gas-phase cell. Since the neutron attenuation coefficient of liquid is significantly larger than that of gas phase, the identification of liquid water droplets in a gas-phase cell is straightforward. When applied to a redox flow battery however, reactants are in liquid phase, so the implementation is the exact inverse: gas-phase products generated within the cell will be detected by greatly reduced neutron attenuation.

For an all vanadium redox flow battery, undesirable side reactions between the liquid electrolyte and porous carbon electrodes or flow field plates can cause gas evolution. Currently, no published studies have attempted to experimentally determine conditions under which these side reactions begin to generate gas within an operating cell. This work  address the implementation of neutron imaging as an in situ diagnostic technique to identify unfavorable operating conditions resulting in side reactions in vanadium redox flow battery systems. Figure 1 demonstrates the viability of this technique by illustrating that gas bubbles, identified by lighter colors, have been generated and detected within an all vanadium redox flow battery. Results from experiments at the National Institute of Standards and Technology Center for Neutron Research will be presented which show the bubble volume and onset of side reaction as a function of electrode materials and operating voltage.

1.  A. Z. Weber, M. M. Mench, J. P. Meyers, P. N. Ross, J. T. Gostick and Q. Liu, Journal of Applied Electrochemistry, 41, 1137 (2011).

2.  D. S. Hussey, D. L. Jacobson, M. Arif, K. J. Coakley, and D. F. Vecchia, Journal of Fuel Cell Science and Technology, 7, 021024 (2010).

3.  A. Turhan, K. Heller, J. S. Brenizer, and M. M. Mench, Journal of Power Sources, 160, 1195–1203 (2006).