Dear Colleagues,

To reduce greenhouse gas (GHG) emissions, we need to move away from fossil-based energy sources. Hydrogen (H₂) is now more broadly considered to be an alternative energy carrier to the fossil fuels. Water electrolysis is an electrochemical energy storage system that harvests energy into the H₂ produced by water splitting utilizing electricity. Particularly in combination with renewable energy sources, such as solar and wind energies, water electrolysis can generate zero-emission clean fuel, i.e., H₂. Ion exchange membrane water electrolysis proposes many advantages, including compact size, high H₂ production rate, and flexibility to the alternating electrical inputs, thus making it a very suitable H₂ production technology for renewable energy sources. Types of ion exchange membrane water electrolysis are proton exchange membrane (PEM) electrolysis and anion exchange membrane (AEM) electrolysis. PEM water electrolysis works in acidic environments and is a relatively mature technology. Commercial PEM water electrolysis systems are available. However, the cost of PEM electrolysis is still very high due to the use of expensive and rare materials (iridium, platinum, and titanium), and cost reduction is highly needed for the broad employment of this technology. AEM water electrolysis works in alkaline environments, making it accessible for use with inexpensive materials, i.e., significant cost reduction is possible. However, AEM electrolysis technology has not been fully developed yet for practical applications, and there are many challenges to make it viable.

This Special Issue is intended to cover both PEM and AEM water electrolysis technologies in order to help grasp the progress and challenges of both technologies and eventually contribute to the advancement of ion exchange membrane water electrolysis technologies.

Dr. Hoon T. Chung
Guest Editor

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• AEM water electrolysis
• PEM water electrolysis
• electrolysis system
• membrane
• ionomer
• catalysts