Surface characterization of Pd/Ag23wt% membranes after different thermal treatments

Thickness dependent effects of solubility and surface phenomena on the hydrogen transport properties of sputtered Pd77%Ag23% thin film membranes

“…The two-step sputtering technique used to obtain the Pd77%Ag23% membranes tested in this work avoids the presence of most potential contaminants, and analysis has confirmed the purity [27,28,34,35]. It is thus believed that impurities are not involved in the solubility variations found in the present work.…”

“…The substrate side is very smooth and characterized by small grains, as reported in Table 1. Increased roughness on the growth side with growing membrane thickness has already been reported for sputtered membranes similar to those applied here [32,35]. Images of the substrate side were previously not reported in literature due to the resolution limitations imposed by the equipment available at the time [32,35].…”

“…The findings have been linked to segregation phenomena [35,42,43,46] as well as roughening of the surface [19,32,35,47,48] and removal of surface impurities [5,42,43,49], but are not fully understood. However, the heat treatment in air is not expected to affect hydrogen solubility in Pd-Ag membranes [19,20].…”

“…100% selectivity, and in configurations where mass transfer limitations in the gas phase can be largely reduced [29][30][31]. We have previously presented results that indicate that the surface as well as the bulk microstructure and composition of the Pd77%Ag23% membranes affect the permeation, and that this may be affected by membrane treatment [32][33][34][35]. Previous investigations also indicate that -depending on the conditions and the pre-treatment of the membrane -surface limitations start to affect the permeation for thicknesses below ~5 µm [36][37][38][39].…”

“…Previous investigations also indicate that -depending on the conditions and the pre-treatment of the membrane -surface limitations start to affect the permeation for thicknesses below ~5 µm [36][37][38][39]. The so-called heat treatment in air, essentially an oxidation-reduction cycle of the surface to a ~2 nm thick oxide [35], has been demonstrated to enhance the hydrogen transport kinetics [19,20,[32][33][34][35][40][41][42][43][44][45] as well as to suppress the competitive adsorption of CO [44].…”