Deposition of Pd–Ag thin film membranes on ceramic supports for hydrogen purification/separation

• Thin film Pd–Ag membranes have been produced for hydrogen selectivity.
• Magnetron sputtering yields Pd–Ag compact films for atomic H diffusion.
• The thin film Pd–Ag membranes yielded a selectivity of α (H2/N2) = 10.

Pd–Ag based membranes supported on porous α-Al2O3 (doped with yttria-stabilized zirconia) were studied for hydrogen selective separation. Magnetron sputtering technique was employed for the synthesis of thin film membranes. The hydrogen permeation flux is affected by the membrane columnar structure, which is formed during deposition. From scanning electron microscopy analysis, it was observed that different sputtering deposition pressures lead to distinct columnar structure growth. X-ray diffraction patterns provided evidence of a Pd–Ag solid solution with an average crystallite domain size of 21 nm, whose preferential growth can be altered by the deposition pressure. The gas-permeation results have shown that the Pd–Ag membrane supported on porous α-Al2O3 is selective toward H2. For optimized membrane synthesis conditions, the permeance toward N2 is 0.076 × 10−6 mol m−2 s−1 Pa−1 at room temperature, whereas for a pressure difference of 300 kPa the H2-flux is of the order of ca. 0.21 mol m−2 s−1, which corresponds to a permeance of 0.71 × 10−6 mol m−2 s−1 Pa−1, yielding a selectivity of α (H2/N2) = 10. These findings suggest that the membrane has a reasonable capacity to selectively permeate this gas.

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