OBSERVATIONS OF UPHILL DIFFUSION OF HYDROGEN IN PALLADIUM AND NICKEL MEMBRANES BY AN ELECTROCHEMICAL PERMEATION METHOD

The ''uphill'' diffusion of hydrogen during permeation through flat sh eets of palladium and nickel has been studied by an electrochemical pe rmeation method at 303 K. For both annealed and as cold rolled Pd samp les, uphill diffusion effects during both hydrogen absorption and deso rption have been observed with initial hydrogen contents ranging from about H/Pd = 0.01 up to H/Pd = 0.25 - 0.3. The non-Fickian permeation fluxes have been associated with lattice volume differences across the (alpha + beta)/beta and (alpha + beta)/alpha interfaces. Influences o f magnitudes of galvanostatic currents and membrane thickness were exa mined. In similar studies with nickel membranes analogous uphill effec ts were observed.