(31e) Developments in Proton Conducting Membranes for Hydrogen Separation and Fuel Cell Applications

Various types of membranes for hydrogen separation at low to high temperature have been reported during the last decades. The most studied are membranes based on microporous materials and dense metals. In recent years considerable attention has been given to dense ceramic proton conducting membranes for high temperature applications. Despite significant fundamental work focusing on identifying materials few systems have been identified with fairly high proton conductivity (>0.01 S/cm). Furthermore, most systems have dominating protonic and low electronic conductivity, making them more applicable as electrolytes for SOFC and H2 pumps rather than H2-separation membranes. Some perovskites with large alkaline earth ions on A-site (Ba, Sr), e.g. cerate-based ceramics appear promising, however, the contribution of oxide ions to the conduction grows markedly as the temperature is raised and these materials are considered as vulnerable to CO2. Although the conductivity of oxides such as LaNbO4 and Ln2Zr2O7 systems is lower than those of the cerates, they are stable against carbon dioxide gas. Their lower conductivity induces constrains in the shaping of the ceramics as thin dense membranes of less than 10 micron thickness are required. In this work we will present an overview of materials that have been investigated and point out some interesting possibilities. Our work focuses on new materials and we will demonstrate how dense proton conducting membranes can be made with thickness of 1-10 micron, and show results from materials testing.