Hydrogen permeation through palladium-nickel-hydroxide film bilayer

The hydrogen permeation through the bilayers of palladium substrate covered with a film of pure nickel hydroxide (Pd-Ni(OH)(2)) and with a film of mixed hydroxide of nickel and cobalt (Pd-Co(OH)(2)-incorporated Ni(OH)(2)) has been investigated by analyzing the measured build-up and decay permeation current transients. Apparent hydrogen diffusivity increased with rising fraction of Co(OH)(2) in the Ni(OH)(2) film, as determined from the build-up permeation current transients, suggests that, at a given hydrogen content, the amount of the hydrogen injected into the Ni(OH)(2) grain interior is reduced by the Co(OH)(2) incorporation. Apparent hydrogen diffusivity determined from the decay permeation current transient is approximately 10(-11) cm(2) s(-1) and there is no significant difference in hydrogen diffusivity between pure and doped Ni(OH)(2) films, irrespective of oxyhydroxide and hydroxide phases involved. This result suggests that the hydrogen transport through pure and doped Ni(OH)(2) films is governed by hydrogen trapping at the trap sites present at the grain boundaries rather than those existing in the grain interior.