Alkaline water electrolysis: with or without iron in the electrolyte?

The presence of iron in the electrolyte has a significant impact on the performance of the electrodes in alkaline water electrolysis. For nickel-based anodes, the presence of iron is needed to achieve and maintain low overpotentials in the oxygen evolution reaction (OER). In contrast, in hydrogen evolution, the presence of iron can lead to deactivation of noble metal-based cathodes, which are more active than non-noble metal cathodes. Since the catholyte and anolyte can mix through the porous separator, stack developers need to decide on the optimal iron content in their system. It seems most promising to focus further development on the ‘iron-rich’ system, also considering the costs of construction materials and water purification.