Hydrogen Diffusion Transport in an All-Iron Flow Battery Rebalance System

Abstract

All-iron flow batteries (IFBs) are being developed for low-cost large-scale energy storage applications. IFBs use abundantly available, non-toxic and low cost electrolyte materials[1]. The all-iron flow battery involves plating and stripping of metallic iron in the negative half-cell and utilizes the Fe II/III (ferrous/ferric) redox couple reaction at its positive electrode[2-3]. Hydrogen evolution occurs as the iron deposits at the negative electrode during the flow battery charging and even if the amount might be small, there will be an impact on the electrolyte balance over many cycles. Recently, Selverston et al.[3] demonstrated a concept of hydrogen rebalance in an all-iron flow battery through designing a capillary-action galvanic reactor (CGR) to consume hydrogen and reduce excess ferric ions in the positive electrolyte reservoir. This design can maintain the balance of protons and reduce undesired precipitation reactions. A tube connects the negative tank headspace where hydrogen collects to the positive tank headspace where the CGR reactor is placed. An understanding of design factors on hydrogen transport through the tube between headspaces is desired and mathematical modeling[4-7] is the approach we took to achieve this. In this poster, we report a mathematical model of hydrogen diffusion between the headspaces of the negative electrolyte tank and the positive electrolyte tank. The effects of dimensional parameters, including diameter of tank, height of tank, diameter of tube, length of tube and diffusion coefficient on hydrogen diffusion rates and partial pressure are investigated during both battery charge and battery standby cases. In Figure 1, we demonstrate that the mathematical model is reasonably validated by the previous published experimental data for a specific all-iron flow battery rebalance device. Acknowledgements This work is supported by the all-iron flow battery project (grant number: DE-AR0000352) funded by Department of Energy (DOE) of the United States.