Optimization of the mixed protonic–electronic conducting materials based on (Nd5/6Ln1/6)5.5WO11.25−δ

Abstract

[EN] 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)5.5WO11.25 d (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 700 1000 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.