Synthesis and hydrogen permeation properties of asymmetric proton-conducting ceramic membranes

Asymmetric proton-conducting SrCe0.95Tm0.05O3−δ membranes consisting of a dense thin film and a thick porous support of the same material were prepared by conventional and cost-effective dry pressing method. Green powder of SrCe0.95Tm0.05O3−δ was prepared by wet chemical method using metal nitrates precursors. Smaller particle size powder was used to make the dense top layer while the larger particle size powder produced porous substrate. The particle size of the powder was revealed to be an important factor that affects the porosity and shrinkage of the sintered disks. A close match between the shrinkage of the support and the top layer led to the defect-free asymmetric disks. The film thickness was varied from 800 μm to 150 μm by varying the amount of the powder in the top layer. H2 permeation flux of these thin films was measured under various operating conditions. The H2 permeation rates were found to be inversely proportional to the thickness of the film indicating that bulk diffusion rather than surface reaction played a dominant role in H2 transport within the studied thickness range (1.6 mm–150 μm). Activation energy of H2 flux was 120 kJ/mol in 600–700 °C which decreased to 20 kJ/mol in 700–950 °C. This indicates a change in the mechanism of protonic/electronic transport around 700 °C.