Hydrogen diffusion through a membrane studied with resonant neutron reflectometry

Resonant neutron reflectometry is a powerful probe of hydrogen absorption in thin layers, offering high depth sensitivity and low measurement time. In the case of a hydrogen barrier layer which hinders diffusion the concentration gradient modifies the resonance conditions in the reflectometric measurement. This can be used to quantify layer-by-layer hydrogen concentrations, while maintaining short measurement times (i. e. 5 s) and fast kinetics capabilities. In this study, we illustrate the sequential hydrogen filling of two Nb layers separated by a ∼ 7 nm Pt/Co/Pt barrier. The broadening and subsequent sharpening of the resonance peak observed during this process carries information about the hydrogen content of the two absorbing layers. The effective diffusion coefficient through the thin barrier was found to be in the order of 10 -19 m 2 s -1 . The results demonstrate the potential of resonant neutron reflectometry for accurate characterization of hydrogen transport in membranes, diffusion barriers, and proton-based functional devices.