Two composites consisting of the proton conducting Ca-doped LaNbO4 and electron conducting LaNb3O9 with, respectively 90 and 70vol% LaNbO4 were prepared by spark plasma sintering. The amount of hydrogen produced at the sweep side was measured as a function of temperature and pH2 gradient under wet and dry sweep gas conditions. The hydrogen flux increases with increasing temperature and feed-side pH2. The flux was significantly higher for the 70 vol% LaNbO4 composite than the 90 vol% LaNbO4 composite. Ambipolar conductivities calculated from the flux data showed the same pH2 dependence for both composites. The electrical conductivity of the 70vol% LaNbO4 composite was characterized as a function of temperature under wet hydrogen. The microstructure and phase distribution of the two composites were analyzed and their transport properties with different flux limiting processes were discussed. An increased hydrogen production with wet compared to dry sweep gas was concluded to reflect water splitting due to transport of oxygen from the permeate to the feed side.

Hydrogen Permeation, Transport Properties and Microstructure of Ca-Doped LaNbO4 and LaNb3O9 Composites. W.Xing, G.E.Syvertsen, T.Grande, Z.Li, R.Haugsrud: Journal of Membrane Science, 2012, 415-416, 878-85