A Comparative Study of Electrode Parameters of Vanadium Redox Flow Batteries for Improved Design and Performance

Abstract

Large-scale energy storage has become an urgent priority to integrate variable renewable energy sources into the electricity grid. Redox flow batteries offer attractive energy storage platforms due to the ease of integration of renewable energy, higher round-trip efficiency, location flexibility, and scalability [1]. Vanadium redox flow batteries (VRFBs) have already received widespread attention due to their recent commercialization for large-scale storage applications [2]. The electrode plays a significant role in determining the performance of the VRFB, which is composed of a porous microstructure characterized by fiber diameter, porosity, specific surface area, and permeability. These properties control various parameters that affect the performance of the VRFB system, such as pressure differences between the inlet and outlet of the electrode, overpotentials, cell potential, and crossover from the membrane. Various studies have reported varying electrode porosity's influence on cell charge-discharge cycles of VRFB systems [3–5]. However, these studies lack a consistent link between porous electrode microstructures and cell performance. Hence, the interrelated nature of the individual parameters and accurately predicting their effect on cell performance pose a challenge in predicting cell performance.In this work, we present a comparative study of porous electrode parameters using a 2-dimensional physics-based model of a VRFB incorporating mass, momentum, charge transport, and kinetics. We have established a consistent relationship between electrode parameters and cell performance which is incorporated into the model to verify the dependency of overpotential, pressure difference, and crossover of ions on porosity and fiber diameter by utilizing a correlation for the surface area and permeability as a function of these parameters in the porous electrode. Pressure difference at the inlet and out of the electrode is one of the driving forces for the crossover of ions across one electrode to another, decreasing with the higher value of fibre diameters during the charging of the cell (as shown in Figure 1(a)). The effect of the operating parameter, flow rate, is negligible on the ion crossover. However, the crossover is impacted by the current, which further increases by increasing the current value, as shown in Figure 1(b). We also found that the system efficiency increases with an increase in the fibre diameter and reaches a maximum at the range of 40-70 µm, but voltage efficiency decreases with the higher value of fibre diameter, as shown in Figure 1(c). This study/analysis/work will include the impact on the crossover of vanadium ions by varying the electrode and operating parameters. The system's efficiency with and without considering the pumping energy will also be presented for various parameters. Our key findings provide important insight for optimizing VRFB design. Developing a 2D model that considers multiple key parameters enables a better understanding of the complex interactions between electrode microstructure and system performance.