Abstract
All-vanadium redox flow batteries (VRFBs) are used as energy storage systems for intermittent renewable power sources. The performance of VRFBs depends on materials of key components and operating conditions, such as current density, electrolyte flow rate and electrolyte composition. Mass transfer overpotential is affected by the electrolyte flow rate and electrolyte composition, which is related to the limiting current density. In order to investigate the effect of operating conditions on mass transport overpotential, this study established a relationship between the limiting current density and operating conditions. First, electrolyte solutions with different states of charge were prepared and used for a single cell to obtain discharging polarization curves under various operating conditions. The experimental results were then analyzed and are discussed in this paper. Finally, this paper proposes a limiting current density as a function of operating conditions. The result helps predict the effect of operating condition on the cell performance in a mathematical model.
Highlights
Intermittent renewable energy sources, such as solar and wind, prompt the requirement for energy storage systems
The limiting current density is related to the flow velocity, and the results showed that the concentration overpotential increased as the electrolyte flow rate decreased
The electrolytes were not recirculated in this vanadium redox flow batteries (VRFBs) system in order to maintain a constant electrolyte concentration for measuring polarization curves
Summary
Intermittent renewable energy sources, such as solar and wind, prompt the requirement for energy storage systems. All-vanadium redox flow batteries (VRFBs), which store or release energy by a redox reaction between vanadium ions exhibiting different charge states in the electrolytes, are considered potential candidates for energy storage [1]. The reactions that occur during charging and discharging can be expressed as the following equations: At the positive electrode: Discharge ⎯⎯⎯⎯ → VO 2+ + H 2 O. VO +2 + 2 H + + e − ←⎯⎯⎯ ⎯ Charge (1). At the negative electrode: → V 3+ + e − V 2+ ←⎯⎯⎯ (2). The efficiency of a VRFB system depends on electrode or separator materials and operating conditions
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