chapter  6
16 Pages

Vanadium–Air Redox Flow Batteries: Fundamentals and Applications

Vanadium-air redox flow batteries (VARFBs) (Figure 6.1a) are modified vanadiumredox flow batteries (VRFBs) [1,2] (Figure 6.1b) that demonstrate higher energy density, 20% higher standard cell voltage [1-10] after replacement of the positive electrode redox couple VO2+/VO2+ with an oxygen reduction reaction (ORR), and reduced cost due to elimination of the most expensive part of the V5+/V4+ electrolyte (43% of the total cost of a VARFB, as shown in Figure 6.2 [9,11]). A bidirectional VARFB system consists of one tank with a circulated anolyte V2+/V3+ solution, a positive air-cathode, an inert negative electrode, an ion exchange membrane (IEM) separating the electrodes and providing proton transport, a sulfuric acid catholyte, inert positive electrodes, a current collector, bipolar plates, frames, heat exchangers, and a power conversion system [8].