Preparation of thin palladium membranes on a porous support with rough surface

Abstract

The integrity of thin composite palladium membranes is influenced by the surface roughness of the porous support. Supports with smooth surface and small pore size are expensive as they are composed of several layers with decreasing pore size which require multiple successive energy and time consuming sintering steps. In addition, smooth surfaces may cause poor membrane adhesion. It is therefore of interest to develop methods for preparation of thin defect-free palladium membranes over supports with rough surfaces. Porous stainless steel tubes coated by atmospheric plasma spraying with a porous layer of yttria-stabilized zirconia (YSZ) were used in this work as a support for palladium composite membranes. The YSZ layer served as a barrier against intermetallic diffusion between the palladium membrane and the metallic support. Three different techniques to create the membranes were compared: magnetron sputtering did not result in sufficiently dense films. Atmospheric plasma spraying produced relatively thick continuous films, but with some residual open porosity. Electroless plating gave the densest layers. Yet rather thick layers were required to limit the number of defects, which is associated with high cost and low hydrogen flux. Activation of the support surface by metal organic chemical vapor deposition of palladium instead of the conventional sensitization and activation pretreatment based on successive immersion in SnCl 2 and PdCl 2 solutions allowed to reduce the membrane thickness without compromising its integrity. The resulting membrane showed significantly higher permselectivity but at the same time decreased hydrogen permeability.