Surface characterization of Pd/Ag23 wt% membranes after different thermal treatments

• Published in: Applied surface science 2010-08, Vol.256 (20), p.6121-6132
• Main Authors: Ramachandran, A., Tucho, W.M., Mejdell, A.L., Stange, M., Venvik, H.J., Walmsley, J.C., Holmestad, R., Bredesen, R., Borg, A.
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Hydrogen permeation; PdAg membranes; Physics; Segregation; Surface topography
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2010.03.131

Hydrogen permeation measurements of 1.5–10 μm thick Pd/Ag23 wt% membranes before and after thermal treatments at 300 °C in air (both sides) or in the temperature range 300–450 °C in N 2 (feed side) and Ar (permeate side) were performed. Accompanying changes in surface topography and chemical composition were subsequently investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profiling. For a 2 μm thick membrane, the surface roughness increased for all annealing temperatures applied, while a temperature of 450 °C was required for an increase in roughness of both membrane surfaces to occur for the 5 μm membrane. The thickest membrane, of 10 μm, showed changed surface roughness on one side of the membrane only and a slight decrease in hydrogen permeance after all heat treatments in N 2/Ar. X-ray photoelectron spectroscopy investigations performed after treatment and subsequent permeation measurements revealed segregation of silver to the membrane surfaces for all annealing temperatures applied. In comparison, heat treatment at 300 °C in air resulted in significantly increased hydrogen permeance accompanied by increasing surface roughness. Upon exposure to oxygen, Pd segregates to the surface to form a 2–3 nm thick oxide layer (PdO), with more complex segregation behavior after subsequent reduction and permeance measurements in pure hydrogen. The available permeance data for the Pd/Ag23 wt% membranes after heat treatment in air at 300 °C is found to depend linearly on the inverse membrane thickness, implying bulk limited hydrogen permeation for thicknesses down to 1.5–2.0 μm.