Storage and separation of hydrogen with the metal steam process

The chemical reaction of metals and metal oxides with steam at elevated temperatures produces pure hydrogen. Therefore certain metals can be used as gas purification and hydrogen storage material. Storage and transport of metals are basic operations, free from safety issues and hydrogen is produced on demand whenever it is needed by passing steam over the solid reactant. Metal is commonly generated by the reduction of the corresponding metal oxide. Different routes like thermal reduction, carbothermic reduction or fused salt electrolysis are possible. In this paper metals are evaluated with regard to their applicability in the metal steam process upon thermodynamics and experimental investigations. Light metals with high oxygen bonding capacity were found to be promising materials for hydrogen storage due to their high storage density. Ge, Mo, W and Fe were found as potential candidates for the separation process with high hydrogen concentration in the product gas and excellent reduction and oxidation capability. However, reduction and oxidation at elevated temperatures cause the solid metals to reduce their surface area due to sintering. As a result the reaction rates decrease significantly after one redox cycle. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.