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.

Automated summary

Mixed protonic and electronic conducting ceramic membranes have great potential in separating pure hydrogen from gas mixtures. This work focuses on finding suitable compositions and optimized fabrication techniques, as well as characterizing the sintering behavior of the material.