Temperature dependent interaction of hydrogen with PdAg nanocomposite thin films revealed by in-situ synchrotron XRD

PdAg nanocomposite alloy thin films were synthesized using a DC magnetron sputtering process to study the structural changes that occur in the alloy film during the process of hydrogenation and dehydrogenation at different temperatures. The atomic composition of the nano-composite film is 88 at % Pd and 12% at Ag, as determined by the EDAX analysis. In-situ synchrotron X-ray diffraction (XRD) has been used to monitor the subtle structural changes that occurred throughout the hydrogenation and dehydrogenation cycles at an interval of 10 s. This aspect has not been addressed so far. In-situ XRD studies reveal that the XRD peak shifts towards a lower angle due to the lattice expansion in the alloy due to hydrogenation. The change in peak shift is found to be different for different temperatures. The present study also shows no hysteresis during the hydrogen absorption and desorption processes. In addition, the results show that (i) the phase segregation has been observed at 250 , (ii) the peak shift during the hydrogenation process at higher temperatures is not significant, whereas the peak shift throughout the process is more rapid and pronounced at ambient temperature

In-situ investigation on hydrogenation-dehydrogenation of Pd–Ag alloy films

The present work reports on synthesis of PdeAg nano-composite films by magnetron cosputteringand the structural changes in the alloy film during hydrogenation and dehydrogenation.Synchrotron X-ray diffraction is employed in-situ to reveal subtle structuralchanges occurring during hydrogenation and dehydrogenation processes, an aspect notinvestigated so far. It is revealed that the nanocomposite film having 88 at% Pd shows theformation of a-phase as an intermediate phase, however, completion of the hydrogenationprocess yields only b-phase. No b-phase formation is observed in nanocomposite thin filmcontaining 54 at% of Pd, suggesting the suppression of formation of b-phase with increasein Ag concentration. On dehydrogenation, the peak returns to its original position i.e. thevalue before hydrogenation. The data also demonstrated that the addition of Ag in Pd resultsin complete removal of dissolved hydrogen thereby eliminates the problem of hysteresis.The study shows that the lower concentrations of Ag in Pd are better in terms ofextent of peak-shift on hydrogenation/dehydrogenation and faster response/recoverykinetics