A vanadium redox battery is used to store electrical energy generated at a wind farm in Tasmania - VCE - SSCE Chemistry - Question 5 - 2009 - Paper 1

The vanadium-containing ion with the highest concentration at the anode when the cell is fully charged is (\text{VO}_2^{+}). At full charge, this ion accumulates as the oxidized form of vanadium.

The balanced overall equation during recharging is:

$\text{VO}^{2+}(aq) + \text{V}^{3+}(aq) + 2H^{+}(aq) \rightarrow \text{VO}_2^{+}(aq) + \text{V}^{2+}(aq) + H_2O(l)$

One major difference is that a vanadium redox cell is rechargeable, while many fuel cells are not. Fuel cells typically consume fuel continuously and require a constant supply of reactants, whereas vanadium redox cells can be recharged and reused.

Using iron as electrode B would lead to the following reaction:

$\text{Fe}^{3+}(aq) + 3e^{-} \rightarrow \text{Fe}(s)$

As iron can react with the electrolyte, it would corrode and degrade, making it unsuitable for use in this cell.