Quantitative assessment of hydrogen diffusion by activated hopping and quantum tunneling in ordered intermetallics

Diffusion of hydrogen in metals is a fundamental process in hydrogen storage in metal hydrides, hydrogen purification by metal membranes, and in hydrogen embrittlement. Quantitative applications of existing models for hydrogen diffusion by activated hopping and quantum tunneling require large scale first principles calculations that are not well suited to metal alloys containing many structurally distinct interstitial sites. We applied a semiclassically corrected version of harmonic transition state theory in conjunction with plane wave density functional theory to examine hydrogen diffusion in multiple C15 Laves phase AB₂ compounds and in bcc CuPd. Comparison with experimental data shows that this theory correctly captures the characteristics of hydrogen diffusion in these materials over a wide range of temperatures. This method is well suited to application in complex alloys.