A subdiffusion framework for hydrogen transport in metallic materials with trapping effects

Hydrogen diffusion and trapping in materials remain critical challenges in understanding hydrogen-induced degradation. Through ergodicity analysis, we demonstrate that hydrogen transport in trap-containing materials deviates from classical Fickian diffusion, exhibiting subdiffusive dynamics. Then we propose a subdiffusion model capturing hydrogen diffusion-trapping behavior in such systems. We establish a subdiffusion model by fractional Fokker–Planck equation to describe this process. The model is validated through reduction to classical Fick’s law and benchmarking against the established McNabb–Foster model. We explicitly elucidate the physical significance of two key parameters: lattice diffusivity and trap index. Furthermore, we develop a non-iterative analytical method to directly extract these parameters from experimental hydrogen permeation transient curves, thereby enabling direct characterization of hydrogen diffusivity and reversible trap properties. The model’s applicability boundaries are delineated.