Hydrogen permeation through copper-coated palladium

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Abstract
The rate of hydrogen uptake and release by metals can be strongly affected by surface barriers for adsorption and desorption. The rate of hydrogen permeation through a Pd membrane was measured for both incident molecules (10−3–10−4 Pa) and neutral atoms (101 6–101 9 H0/m2⋅ s) for membrane temperatures of 300–570 K. The pressure dependence of H2‐driven permeation was used to identify regimes where the permeation was controlled by bulk processes (diffusion‐limited) and surface processes (surface‐limited). The dependence of the H0‐driven permeation rate on the direction of permeation was used to separate the contribution of each surface to the overall surface‐limited permeation rate. One of the membrane surfaces was coatedin situ with copper evaporated from a hot source. This same surface could be monitored in situ by Auger electron spectroscopy. At temperatures below 450 K, stable coppercoatings were made with thicknesses ranging from ∼3 to 25 nm. The thin Cucoatings led to a decrease in the H2‐driven permeation rate. The permeation rate was found to increase, however, for H0 atoms incident on the Cu‐coated surface. This is consistent with a barrier for H2 dissociation and H recombination at the Cu/vacuum interface. Membranes with such a barrier, in conjunction with a source of H0 atoms, have applications as hydrogen pumps.