High flux palladium silver alloy membranes fabricated by microsystem technology

In this study, hydrogen selective membranes have been fabricated using microsystem technology. A 750 nm dense layer of Pd (77 wt%) and Ag (23 wt%) is deposited on a non-porous 1 mm thick silicon nitride layer by cosputtering of a Pd and a Ag target. After sputtering, openings of 5 μm are made in the silicon nitride layer to create a clear passage to the Pd/Ag surface. As a result of the production method, these membranes are pinhole free and have a low resistance to mass transfer in the gas phase, as virtually no support layer is present. The membranes have been tested in a gas permeation system to determine the hydrogen permeability as a function of temperature, gas flow rate, and feed composition. In addition, the hydrogen selectivity over helium has been determined, which appears to be above 1500. At 0.2 bar partial hydrogen pressure in the feed, the hydrogen permeability of the membranes has been found to range from 0.02 to 0.95 mol.H2/m2×s at 350 and 450°C, respectively. It is expected that by improving the hydrodynamics and increasing the operation temperature, substantially higher fluxes will be attainable.