Microsystem technology for high-flux hydrogen separation membranes

The application of thin hydrogen-selective membranes suffers from the occurrence of pinholes and a significant resistance to mass transfer in the porous support. To overcome these problems, Pd, Pd/Ag and Pd-Ta-Pd membranes with a thickness between 0.5 and 1.2 mum have been deposited on a dense and smooth surface of a silicon wafer. After membrane deposition, the underground has been etched to release the membrane surface for H-2 permeation. Membranes have been prepared with a 1 mum thick microsieve as the support or without support. The prepared membranes have been characterized by the H-2 and He flux as a function of temperature (623-723 K) and feed composition (0 < pH(2) < 0.83 bar). The highest H-2 flux, 3.6 mol H-2/(M-2 s), has been found with a microsieve supported 1 mum thick Pd/Ag membrane at 723 K and 0.83 bar hydrogen partial pressure. The fluxes measured here are approximately one order of magnitude higher than the fluxes reported in the literature for Pd or Pd alloy membranes deposited on porous supports. Moreover, helium could not be detected in the permeate, thus indicating the absence of pinholes. (C) 2004 Elsevier B.V. All rights reserved.