Enhancement of Hydrogen Uptake Rates for Nb and Ta by Thin Surface Overlayers

It is shown that thin layers of Pd or Pt enhance the uptake rate of hydrogen into bulk Nb with almost every hydrogen atom that hits the surface passing into the bulk. A model for the kinetics is formulated showing that in a composite-system large uptake rates are achieved by combining the surface properties of Pd with the bulk properties of Nb, thereby resulting in a smaller barrier for migration into the bulk.