Rethinking high-pressure x-ray photoelectron spectroscopy for the study of hydride-forming materials
(2014) 8th International Symposium Hydrogen & Energy — Location: Zhaoqing, P.R. China
Files
No attached file found for this publication.
Details
- Authors
- Abstract
- XPS is a powerful tool for the surface analysis of various materials, providing insightful information about the elements present on a given surface, including their respective chemical state and concentrations across a few up to a few tens of atomic layers. Therefore, XPS is a key experimental technique regarding the understanding of surface phenomena occurring during the formation and decomposition of hydrides, provided that the latter critically influence the efficiency of applications such as solid-state hydrogen storage, hydrogen permeation and hydrogen sensors. However, the short mean free path of electrons with energies below 1500 eV in a gas at ambient pressure does not allow XPS analyses to be performed in realistic experimental conditions from the applications point of view. So does the required vacuum level for X-ray anodes and channeltrons. These problems can be overcome by performing so-called “environmental”, “ambient-pressure” or “high-pressure” XPS [1]. These techniques rely on the use of differential pumping stages, the minimization of the sample-aperture distance in the high pressure regions and, for the most recent systems, on the addition of electrostatic lenses to focus the electrons through the differential pumping scheme [2]. Nonetheless, these techniques suffer from drawbacks, i.e. reduction of the energy resolution and sample freedom of movement, high cost and accessibility of the facilities due to the fact that most of them have been developed for operation at synchrotron light sources. A new experimental approach is proposed here in order to study materials exposed to high hydrogen pressures while keeping the analysis chamber in high vacuum. A new type of sample holder has been designed in this respect, consisting of a Pd-Ag membrane fed on one side with a high hydrogen pressure, and exposed on the other side to the X-ray beam at UHV compatible pressures. Since this alloy exhibits low dissociation barrier, the proper hydrogen absorption enthalpy and fast hydrogen diffusion kinetics, monoatomic hydrogen is rapidly generated and transferred through the bulk of the membrane to the surface exposed to vacuum. Moreover, this also results in a high hydrogen concentration on that surface, because the hydrogen permeation is limited by desorption from the low pressure side of the membrane. By capping the membrane with any hydride-forming material, one is then able to study hydrides by means of XPS with realistic hydrogen concentrations. This new experimental approach will be presented, with particular focus on the effect of the surface properties on the hydrogen permeation through Pd-Ag membranes.
- Affiliations
Swiss Federal Laboratories for Materials Science and Technology Laboratory for Hydrogen and Energy
Citations
Delmelle, R., Gehrig, J. C., Callini, E., Stadie, N., Hosoglu, F., Borgschulte, A., & Züttel, A. (2014). Rethinking high-pressure x-ray photoelectron spectroscopy for the study of hydride-forming materials. 8th International Symposium Hydrogen & Energy, Zhaoqing, P.R. China. https://hdl.handle.net/2078.5/238312