Development of ternary Pd–Ag–TM alloy membranes with improved sulphur tolerance

Resistance to H2S is important for the use of Pd-based membranes in fossil-fuel power stations with integrated carbon capture. In this paper, we present results on the development of ternary Pd–Ag–TM alloy membranes encompassing membrane manufacturing followed by appropriate characterisation, and extensive H2 permeation evaluation. A selection of four ternary Pd–Ag–TM alloy membranes has been prepared by magnetron sputtering with thickness in the range of 1.9–2.4 μm. The H2 permeation properties in 90% H2 in N2 have been determined in terms of H2S inhibition degree and subsequent H2 flux recovery rate. At 20 ppm H2S, the largest effective H2 permeability equal to 1.0×10−9 mol m−1 s−1 Pa−0.5 has been obtained for the Pd75Ag22Au3 membrane. This value for the permeability is a factor of 2 larger compared to the Pd77Ag23 membrane, which shows an effective H2 permeability equal to 5.0×10−10 mol m−1 s−1 Pa−0.5 in the presence of 20 ppm H2S. No evidence of a roentgen-crystalline sulphide phase formation on the alloy surface is observed in the XRD pattern of exposed Pd75Ag22Au3, Pd76Ag21Mo3 and Pd69Ag27Y4 films. Even after 500 h of exposure to 20 ppm of H2S, these films show the same single phase fcc structure. Analysis by XPS, however, shows large segregation and oxidation effects for the Pd76Ag21Mo3 and Pd69Ag27Y4 film, in addition to large sulphur levels. Only in the Pd75Ag22Au3 sample no sulphur is observed by XPS analysis. This indicates that the addition of small amounts of Au to the high-flux Pd–Ag alloy membrane has improved the sulphur tolerance of this alloy, and that this could be an interesting approach in the development of high-flux Pd-based alloy membranes with improved sulphur tolerance.

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► Novel approach for the development of Pd–Ag–TM alloy membranes with improved sulphur tolerance presented.
► H2 permeation properties of four ternary Pd–Ag–TM alloy membranes is presented.
► Pd75Ag22Au3 shows an improved performance in the presence of H2S over Pd85Au15 and Pd70Cu30.
► No evidence of crystalline sulphide phase on the exposed Pd75Ag22Au3, Pd76Ag21Mo3 and Pd69Ag27Y4 alloys.
► Only in the Pd75Ag22Au3 sample no sulphur is observed by XPS analysis.