Impact of Impurities on Water Electrolysis: A Review

Low temperature water electrolysers such as Proton Exchange Membrane Water Electrolysers (PEMWEs), Alkaline Water Electrolysers (AWEs), and Anion Exchange Membrane Water Electrolysers (AEMWEs) are known to be sensitive to water quality, with a range of common impurities impacting performance, hydrogen quality and device lifetime. Purification of feed water adds to cost, operational complexity, and design limitations, while failure of purification equipment can lead to degradation of electrolyser materials and components. Increased robustness to impurities will offer a route to longer device lifetimes and reduced operating costs but understanding of the impact of impurities and associated degradation mechanisms is currently limited. This critical review offers, for the first time, a comprehensive overview of relevant impurities in operating electrolysers and their impact. Impurity sources, degradation mechanisms, characterisation techniques, water purification technologies and mitigation strategies are identified and discussed. The review generalises already reported mechanisms, proposes new mechanisms, and provides a framework for consideration of operational implications.