Highly Durable Composite Palladium Membrane Prepared By Introducing a Metallic Interlayer and a Surface Alumina Coating Layer below 573 K

For the last two decades, several ways such as electroless-plating, electroplating, sputtering and chemical vapor deposition have been proposed to prepare a composite type of thin palladium membrane, whereby improving the hydrogen permeability significantly. However, it has been pointed out that the durability of palladium composite membrane especially at low temperatures is not enough for practical use. Thin palladium film is well known to expand and contract by hydrogen absorption and desorption, leading to peel-off from its support and crack. These defects, in general, are apt to result from an increase in the hydrogen solubility with lowering temperature. Furthermore, the Kirkendall void, which is known as small voids produced around a heterogeneous metal grain attached on palladium film, results in a leakage of gases other than hydrogen.

   In this study, an approach is explored to avoid such occurrences of defects. We propose here a method to depress a deformation of thin palladium film by introducing a metallic interlayer. The hydrogen-absorbed palladium film produces an inner stress accompanied by expansion, which induces cracks and peel-off. We infer that such defects should be depressed if the palladium film adheres tenaciously to the porous support. For that, metallic layer like platinum is thinly deposited on the support, then followed by palladium deposition, showing an important role of preventing the deformation completely. As the countermeasure to the Kirkendall void, surface coating with alumina sol onto the palladium film is employed, thereby enabling to prevent direct contact with other metal particle from catalyst etc.

   An alumina coated Pd/Pt/porous anodic alumina disk membrane was prepared. Hydrogen permeation tests in the range of 373 k – 573 K proved that a new type of composite membrane could maintain its high hydrogen permeability and selectivity without an increase of leakage.