Hydrogenation kinetics of metal hydride catalytic layers

Abstract

Catalyzing capping layers on top of metal hydrides are often employed to enhance the hydrogenation kinetics of metal hydride based systems such as hydrogen sensors. Here, we experimentally study the hydrogenation kinetics of capping layers composed of several alloys of Pd and Au as well as Pt, Ni and Ru, all with and without an additional PTFE protection layer using a novel method and under the same set of experimental conditions. 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 of the activation energy. The kinetics of non-Pd based materials turns 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 green economy. In addition, the developed method can be used to simultaneously study the hydrogenation kinetics and determine diffusion constants in thin film materials for a wide set of experimental conditions.