Fabrication of a Novel BaCe0.8Y0.2O3-δ - Cu Ceramic-Metallic Composite Membrane for Hydrogen Separation

This presentation details the first report of a dense BaCe_0.8Y_0.2O_3-δ–Cu (BCY-Cu) ceramic-metallic (cermet) membrane for high-temperature hydrogen separation. Such a composite may have applications in catalytic partial oxidation of methane (CPOX), steam reforming of methane, the gasification of carbonaceous materials, and methane dehydroaromatization (MDA). BCY serves as the proton conductor, while Cu provides electronic conductivity for electronic-charge compensation. A novel molten-copper infiltration technique is used to form a dense cermet membrane by infiltrating a porous BCY skeleton.

The BCY skeleton fabrication begins with mixing appropriate amounts of BaCO_3, CeO_2, and Y₂O₃ powders with a mortar and pestle, followed by calcination in air. The phase-purity of the resulting powder is verified by X-ray diffraction spectroscopy. Binder is added to the powder via wet-milling with water, followed by pan drying. The powder is crushed with a mortar and pestle, and sieved to achieve a uniform particle size distribution. Pellets are formed by uniaxial dry-pressing, and subsequently sintered at 1600 °C in air, creating a skeleton with approximately 50 % open porosity (Figure 1a). 

This porous BCY skeleton is then infiltrated with copper. Cu and CuO powders are mixed with a mortar and pestle to form a powder containing 8 at.% O. This powder is uniaxially pressed into pellets, which are placed on top of the BCY skeleton. The skeleton and Cu-CuO pellet are placed into a controlled-atmosphere furnace, and heated to 1200 °C in a 330-ppm-oxygen environment (balance argon). Under these conditions, the liquid Cu spontaneously infiltrates the BCY skeleton. While dwelling at 1200 °C, the gas environment is changed to a 10 mol.% hydrogen environment (balance argon), and the sample is cooled.

Cu will not wet, nor infiltrate, a BCY skeleton in a reducing environment, which necessitates the initial heating in the oxidizing environment. Once the Cu-CuO alloy infiltrates the BCY skeleton at high temperature, the environment can be switched to a reducing environment without the Cu-CuO alloy defiltrating the BCY skeleton, due to capillary pressure. The reducing environment removes the O from the alloy, leaving pure Cu metal. An electron micrograph of a polished-cross section of the resulting membrane (Figure 1b) reveals that the cermet is nearly fully dense. Our current efforts focus on hydrogen permeation measurements through these novel cermets.

Figure 1: (a.) Scanning electron micrograph of BCY skeleton after sintering, and (b.) scanning electron micrograph of BCY-Cu membrane, in which the dark phase is Cu and the light phase is BCY.