Yttrium zirconate electrolyte

In addition to fluorite structure electrolytes such as stabilised zirconia and ceria, there are many non-fluorite structure oxides which are potentially attractive for SOFC electrolyte application. These include perovskites like lanthanum gallate and to a lesser degree calcium titanate. Alternative oxides are the pyrochlores such as yttrium zirconate (YZr207)and gadolinium titanate (Gd2Ti207) [49,50], but these are only suitable in very limited oxygen pressure ranges. Therefore, the main discussion here focuses on the perovskites. 

Advances in electrochemical systems rest in large measure with the evolution of new materials that exhibit chemical stability in severe environments, high electrocatalytic activity, rapid ion conductivity, etc. Examples include RuOx-TiOy-Ti electrocatalysts, the polymer Nafion, yttrium-stabilized zirconate and beta-alumina electrolytes, and metastable alloys produced by rapid solidification processing. 

Consequently, we are in the startup phase of our program. Our first task was to identify candidate perovskite oxide materials with high protonic conductivities. We have identified ytterbium doped strontium cerate and yttrium doped strontium zirconate materials as possible electrolyte materials. Barium cerate perovskites exhibit higher protonic conductivity, but the reactivity with carbon dioxide would require pretreatment of the steam. 

In the hydrogen electrode, usually platinum is applied as electrode material on account of its outstanding catalytic capabilities and its chemical stability. It mostly is Teflon bonded or covered by microporous Teflon membranes (plastic net in Fig. 1.33) to make the surface hydrophobic and so prevent the formation of thicker layers of water that would hinder gas access. The electrolyte is immobilized by soaking fiber felts or knitted textiles of mineral fibers (fuel-cell-grade asbestos paper) or zircon fibers stabilized with yttrium (Zircar cloth). They provide high temperature resistance and chemical resistance for long-life batteries. 

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