Kinetics of the atomic structure of palladium nanoparticles during the desorption of hydrogen according to X-ray diffraction

The process of desorption of hydrogen from small palladium nanoparticles is monitored by time-resolved synchrotron X-ray diffraction. Changes in the diffraction patterns corresponding to the transition from the palladium $\beta$-phase to the $\alpha$-phase are detected with an accuracy of 0.3 s. The model of the continuous change in the size of the $\beta$-phase region can be excluded, since the Rietveld analysis does not reveal a broadening of the diffraction peaks corresponding to the palladium lattice during desorption. The theoretical simulation shows the presence of a surface/core interface with different average cell parameters. However, the near-surface layers of the nanoparticle make a lower contribution to the observed diffraction reflections because of a lower crystallinity. The cell parameter in the nanoparticle core depends on the hydrogen concentration both in the core itself and in the shell due to the presence of stresses at the interface.