A comparison of hydrogen diffusivities in Pd and CuPd alloys using density functional theory

Plane wave density functional theory (DFT) is used to examine the binding and diffusion of dilute interstitial H in pure Pd, disordered fcc Cu48Pd52, and ordered bcc Cu50Pd50. Once zero-point (ZP) corrections and lattice relaxations are taken into account, the diffusion activation energy for interstitial H in pure Pd is in quantitative agreement with experimental data. Our DFT results indicate that the diffusion activation energy for interstitial H in ordered bcc Cu50Pd50 is over an order of magnitude smaller than that for pure Pd. We present a detailed description of the range of diffusion activation energies available for local hops of interstitial H in disordered fcc Cu48Pd52 and describe how the net activation energy for long-range H diffusion in this material can be inferred from these results. The variation in H binding energies and diffusion activation energies of interstitial H in bcc and fcc CuPd alloys as a function of alloy composition is also discussed.