Developing High Surface Area Flow through Electrodes with Enhanced Electrical Conductivity for Flow Battery Application
Authors: Murtaza Muhammad Awais , Gostick Jeff T. 
Published: February 2020

With rapidly mounting environmental concerns, coupled with increased energy demand and impending depletion of fossil fuel reserves, there has been a strong focus on developing advanced technologies for a renewable energy infrastructure. Alternative energy sources, though environmentally friendly, are intermittent thus require large-scale energy storage to buffer the temporal mismatch between power generation and power consumption. Flow batteries are a leading candidate for this role due to their decoupled energy and power capacity [1]. Since they were first proposed by NASA in the 1970’s, numerous iterations have been made, but commercialization has been hindered by their high cost, but there is hope this can be addressed by better cell designs [2].

The energy and power density of flow batteries are generally lower than that of lead-acid, lithium-ion and nickel metal hydride batteries [3]. Decreasing the various resistances within the flow battery system via improving electrical conductivity of the electrode is a promising route to improve cell performance. Improving the electrical conductivity of the electrode will result in higher efficiency of the cell, as current flow more easily reducing ohmic losses. Improving efficiency means more power can be obtained from a given amount of electrolyte. Therefore, performance will be improved and capital cost will be lowered as less electrolyte will now be required to meet a specific power generation targets.

The electrospining technique has been recently investigated as a means of producing high performance electrodes, via small fibers and very high porosity [4]. High porosity means presence of much less solid material, which in turn leads to higher resistance within the electrode as fewer electron flow paths exist. This presentation will report the developments made towards increasing the electrical conductivity of high porosity electrospun fibers of polyacrylonitrile, such as varying the sintering/carbonization conditions, impregnating the fibrous mat with conductive filler, and pre-treating the material prior to carbonization to improve inter-fiber contacts. Figure 1 & 2 show SEM images for electrospun fibers of polyacrylonitrile before and after pre-treatment prior to carbonization.

The developed materials were characterized for their structural (i.e. fibre morphology, porosity) and transport properties (i.e. diffusivity, permeability). These parameters closely correlate with cell performance and are crucial for the developmental phase, before the final product can be tested in a pilot scale test cell. As improving electrical conductivity is the primary focus of the research, Figure 3 shows a graph of how the developments of this research have enhanced the previously mentioned property.

REFERENCES

[1] A. Z. Weber, M. M. Mench, J. P. Meyers, P. N. Ross, J. T. Gostick, and Q. Liu, “Redox flow batteries: A review,” J. Appl. Electrochem., vol. 41, no. 10, pp. 1137–1164, 2011.

[2] L. H. Thaller, “Electrically rechargeable REDOX flow cell,” US3996064 A, 07-Dec-1976.

[3] M. R. Mohamed, S. M. Sharkh, and F. C. Walsh, “Redox flow batteries for hybrid electric vehicles: Progress and challenges,” 5th IEEE Veh. Power Propuls. Conf. VPPC ’09, pp. 551–557, 2009.

[4] S. Liu, M. Kok, Y. Kim, J. L. Barton, F. R. Brushett, and J. Gostick, “Evaluation of Electrospun Fibrous Mats Targeted for Use as Flow Battery Electrodes,” J. Electrochem. Soc., vol. 164, no. 9, pp. A2038–A2048, 2017.

Figure 1