Repeated hydrogenation of 20 nm Pd films was investigated by in situ X-ray diffraction.

Hydride precipitates form coherent interfaces with matrix in nanocrystalline and epitaxial thin films.

Grain boundaries affect precipitation of the hydride phase in the nanocrystalline film.

Stress in epitaxial film is tensile due to different thermal expansion of Pd and sapphire.

After hydrogen absorption/desorption cycle the stress in both films becomes tensile.