Palladium membranes prepared by r.f. magnetron sputtering for hydrogen purification

Pd thin films, 5-μm thick, were deposited by r.f. magnetron sputtering on porous stainless steel discs (0.5 μm rejection grade) as membrane for hydrogen filtering. In order to fill the steel pores and prepare a flat surface for the Pd coating, a polymeric layer made of commercial polycarbonate was deposited on the steel surface by spin coating technique. The PC layer shows a relatively smooth surface morphology and strong adhesion to the porous substrate. Secondary electron microscopy analysis of the fractured sample shows, in fact, branches of polymeric material which depart from the PC surface and enter in the substrate pores for length ∼10 μm ensuring the necessary anchorage. Palladium sputter deposition produced rough and pinholes free Pd coating well adherent to the PC buffer layer. Gas selectivity tests by permeation analysis evidenced an hydrogen permeance of 5×10−1 μmol m−2 s−1 Pa−1 of the as-prepared Pd–PC composite membrane and high H2 to N2 selectivity.