Current Distribution Analysis of Different Cell Geometries for Redox Flow Batteries
Authors: Cervantes-Alcalá Rogelio , Rivera Fernando Felipe , Miranda-Hernández Margarita 
Published: February 2020

Redox flow batteries (RFBs) have attracted attention in the last years as energy storage devices at medium and large scale. This technology offers different advantages like high efficiencies, decoupling the power and energy storage capacities, and relatively ease scalability1. However, despite RFBs have been studied since more than 30 years, its implementation at the industrial scale is scarce2. To achieve a successful scale-up of these devices, it is important to introduce a well-established design procedure from the laboratory scale. Furthermore, the redox flow battery technology lacks of its own geometry design since most authors have adapted geometries from the fuel cell technology3.
The fact that the geometries are not designed for the redox flow battery technology can derive in serious issues of transport phenomena. These problems go from bad flow distribution to large potential differences across the electrode causing secondary reactions. For this reason, it is necessary to introduce innovative geometry designs for RFBs. To reach this goal the design of new geometries assisted by computational tools is an alternative approach, considering that experimental work can be expensive and highly time consuming. The design assisted by computational tools is based on the study of transport phenomena such as momentum transfer (hydrodynamics), mass transport and potential/current distribution inside of the electrochemical cell. The analysis of these phenomena is crucial to determine its impact on the RFBs performance.
In this work a new cell geometry is proposed, which has been design by means of computational tools. As mentioned previously, current cell geometries used for redox flow batteries were adapted from the fuel cell technology, where the cells are square. In this case, the cell geometry is proposed with a different width-high ratio based on geometries similar to electrochemical reactors. Also, the implementation of turbulence promoters is proposed as an alternative to classical flow fields. To make evident differences in the geometries, a comparison between a square geometry with an interdigitated flow field and the new geometry in the presence of a net-like spacer (turbulence promoter) is realized. The comparison includes flow distribution, mass transport and potential/current distribution analysis in both geometries.
The results show that the flow distribution is inadequate in the square geometry, the presence of the interdigitated flow field generates stagnant zones and high velocity zones. While for the new geometry a more homogeneous distribution was observed, without recirculations and stagnant zones. The simulation of the injection of a tracer molecule makes evident the deviation of the flow distribution in the typical geometry, reflected on longer retention times compared to the new geometry (Fig.1). The impact of the flow distribution on mass transport and potential/current distribution is notorious. Since the potential/current distribution is dependent on the mass transport and concentration gradients, the new geometry showed a more homogeneous distribution due to the better flow distribution. Based on the results shown here, the proposed geometry is a promising alternative to the typical square geometry for redox flow battery applications.

References

P. Alotto, M. Guarnieri, and F. Moro, Renew. Sustain. Energy Rev., 29, 325–335 (2014).

L. F. Arenas, C. Ponce de León, and F. C. Walsh, J. Energy Storage, 11, 119–153 (2017) http://dx.doi.org/10.1016/j.est.2017.02.007.

T. Jyothi Latha and S. Jayanti, J. Appl.
Electrochem., 44, 995–1006 (2014).

Figure 1