Up-scaling and processing related characterisation of hydrogen permeation membranes based on pristine and Mo substituted La28_xW4+xO54+1.5x

Mixed protonic and electronic conducting ceramic membranes offer a high potential to separate pure hydrogen from gas mixtures or in the field of membrane reactors. The water-gas-shift reaction is an example for the possible application of lanthanum tungstate based materials with general formula La28_xW4+xO54+1.5x (LaWO) due to their high stability under the reaction conditions. To bring ceramic membranes one step closer to com-mercialisation, high effort is needed to find optimised material compositions and transfer them into suitable fabrication techniques. Both is done in the present work. First, a detailed XRD-study, supported by micro -structural analysis, was performed to find a suitable composition for Mo-substituted LaWO. As it was demon-strated, with increasing the Mo concentration as a substitute for W leading to enhanced electronic conductivity, the single phase region narrows and La/W ratio shifts to the higher values. In order to ensure single phase composition of the powder used in the membrane fabrication, 20 mol.% Mo substituted LWO was the material of choice. Subsequently tape-casting was performed to produce asymmetric membranes consisting of a thin func-tional membrane made of LaWO-Mo20 and a porous support layer of pure LaWO. Such asymmetric component could be scaled-up to 100 cm2 active membrane area. The sintering behaviour was characterised by optical dilatometry. The more cost-efficient support material MgO was shown to be incompatible with the LaWO-Mo20 material. Therefore, an advanced fabrication route was developed by introducing an intermediate layer to overcome interdiffusion and secondary phase formation.