Two composites consisting of the proton conducting Ca-doped LaNbO4 and electron conducting LaNb3O9 with, respectively 90 and 70 vol% LaNbO4 were prepared by spark plasma sintering. The amount of hydrogen produced at the sweep side was measured as a function of temperature and p(H2) gradient under wet and dry sweep gas conditions. The hydrogen flux increases with increasing temperature and feed-side p(H2). The flux is significantly higher for the 70 vol% LaNbO4 composite than the 90 vol% LaNbO4 composite. Ambipolar conductivities calculated from the flux data showed the same p(H2) dependence for both composites. The electrical conductivity of the 70 vol% LaNbO4 composite was characterized as a function of temperature under wet hydrogen. The microstructure and phase distribution of the two composites are analyzed and their transport properties with different flux limiting processes are discussed. An increased hydrogen production with wet compared to dry sweep gas is concluded to reflect water splitting due to transport of oxygen from the permeate to the feed side. (c) 2012 Elsevier B.V. All rights reserved.