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

Abstract Resistance to H 2 S 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 H 2 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 H 2 permeation properties in 90% H 2 in N 2 have been determined in terms of H 2 S inhibition degree and subsequent H 2 flux recovery rate. At 20 ppm H 2 S, the largest effective H 2 permeability equal to 1.0×10 −9  mol m −1  s −1  Pa −0.5 has been obtained for the Pd 75 Ag 22 Au 3 membrane. This value for the permeability is a factor of 2 larger compared to the Pd 77 Ag 23 membrane, which shows an effective H 2 permeability equal to 5.0×10 −10  mol m −1  s −1  Pa −0.5 in the presence of 20 ppm H 2 S. No evidence of a roentgen-crystalline sulphide phase formation on the alloy surface is observed in the XRD pattern of exposed Pd 75 Ag 22 Au 3 , Pd 76 Ag 21 Mo 3 and Pd 69 Ag 27 Y 4 films. Even after 500 h of exposure to 20 ppm of H 2 S, these films show the same single phase fcc structure. Analysis by XPS, however, shows large segregation and oxidation effects for the Pd 76 Ag 21 Mo 3 and Pd 69 Ag 27 Y 4 film, in addition to large sulphur levels. Only in the Pd 75 Ag 22 Au 3 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.