Abstract
The tungstates Ln6WO12 are proton conducting materials exhibiting mixed (protonic and electronic)
conductivity and remarkable stability in moist CO2 environments. Hydrogen-permeable membranes
made of this kind of material find application in industrial gas separations such as hydrogen separation
from hydrogen containing gases, for the implementation of pre-combustion strategies in fossil-fuel
power plants and catalytic membrane reactors. This work presents a thorough characterization
(structure, conduction and hydrogen permeation) of mixed conducting materials on the specific system
(Nd5/6Ln1/6)5.5WO11.25d (Ln: La, Ce, Pr, Eu, Tb). The evolution of the crystal structure and crystallite size
was studied as a function of the lanthanide dopant. The total conductivity in different environments was
investigated as a function of pO2 and temperature. Furthermore, the H/D isotopic effect and the
hydration effect were also studied in reducing and oxidizing atmospheres by DC conductivity
measurements. Hydrogen permeation was measured for all compounds in the range of 7001000 C
studying the effect of pH2 and the hydration degree of the membrane depending on the lanthanide
dopant. Finally, the chemical stability of these materials at 800 C was evaluated in contact with a
humidified CO2-rich gas stream.
