Catalyzing capping
layers on metal hydrides are employed to enhance
the hydrogenation kinetics of metal hydride-based systems such as
hydrogen sensors. Here, we use a novel experimental method to study
the hydrogenation kinetics of catalyzing capping layers composed of
several alloys of Pd and Au as well as Pt, Ni, and Ru, all with and
without an additional PTFE polymer protection layer and under the
same set of experimental conditions. In particular, we employ a thin
Ta film as an optical indicator to study the kinetics of the catalytic
layers deposited on top of it and which allows one to determine the
absolute hydrogenation rates. Our results demonstrate that doping
Pd with Au results in significantly faster hydrogenation kinetics,
with response times up to five times shorter than Pd through enhanced
diffusion and a reduction in the activation energy. On the other hand,
the kinetics of non-Pd-based materials turn out to be significantly
slower and mainly limited by the diffusion through the capping layer
itself. Surprisingly, the additional PTFE layer was only found to
improve the kinetics of Pd-based capping materials and has no significant
effect on the kinetics of Pt, Ni, and Ru. Taken together, the experimental
results aid in rationally choosing a suitable capping material for
the application of metal hydrides and other materials in a hydrogen
economy. In addition, the used method can be applied to simultaneously
study the hydrogenation kinetics in thin-film materials for a wide
set of experimental conditions.