Effect of diffusion coefficient variation on interrelation between hydrogen diffusion and induced internal stress in hydrogen storage alloys

Abstract

A diffusion behavior of hydrogen in a hydrogen storage alloy is affected by not only hydrogen concentration but also the stress induced by hydrogen atom expanding the lattice of the alloy. The uphill diffusion in which hydrogen diffused against the concentration gradient due to the stress has been observed. Moreover, the fugacity of hydrogen in the alloy deviates from unity significantly even at low hydrogen concentration, which decreases the flux.In this paper, the effect of the stress and the diffusion coefficient variation with the concentration on hydrogen diffusion at low concentration was investigated using the finite element analysis. As a result, the variable diffusion coefficient model combined with the stress effect showed better agreement with the experimental result than Fick's diffusion models and the constant coefficient SID model. It was concluded that the effect should be considered even if the concentration is low.