Palladium-composite membranes: Synthesis, characteristics and properties

Inorganic composite Pd-based membranes may be used in a variety of technological processes such as hydrogen separation and purification, hydrogen recovery from process streams, and membrane reactors for hydrogen-related reactions. In this work, we focus on several issues related to dense thin Pd-based composite membranes, prepared by electroless plating and a new technique, which combines electroless plating and osmosis.; Based on data obtained mainly by using an atomic force microscope, the kinetics of different microstructural parameters describing the formation of thin palladium films on porous Vycor glass by the electroless plating technique are presented. It is shown that palladium films deposited by electroless plating with osmosis have finer grained and more uniform microstructure as compared to conventional technique. A physical model that describes the role of osmosis during the electroless plating process is also developed. The influence of osmosis on metal penetration into porous Vycor glass is studied, and new approach for substrate activation is developed. It appears that use of osmosis during seeding contributes more to microstructural uniformity, while during plating it leads to finer Pd grain size of plated films.; The permeation behavior of hydrogen through palladium composite membranes is analyzed using a resistance model in order to separately obtain permeation parameters of the support and palladium layer, respectively. It is shown that osmosis during electroless deposition allows one to change hydrogen flux through Pd composite membranes not only by decrease of film thickness but also by change of Pd film microstructure. Moreover. we confirm for the first time that for membranes prepared by the same technique, with gradually changing microstructural characteristics, those with smaller palladium crystallites exhibit larger hydrogen flux. It Is also shown that owing to osmosis-enhanced penetration of metal into porous support, the synthesized membranes are thermally and mechanically more stable.; These features make osmosis a powerful tool to synthesize Pd-composite membranes with high hydrogen permeability and superior thermal and mechanical properties for a wide variety of applications.