Electrical conduction and hydrogen permeation through mixed proton-electron conducting strontium cerate membranes

The electrical conduction and hydrogen permeation properties of dense SrCe_0.95Tm_0.05O_3-δ (SCTm) membranes were studied in the temperature range of 600-950 °C. The conductivity measurement shows that the temperature dependence of SCTm conductivity obeys the Arrhenius relationship in atmospheres of O₂, air, N₂ and 10% H₂/He. The presence of water vapor lowers both the conductivity values and the activation energies in oxidative atmospheres, suggesting a mixed proton-electron conducting property of the membrane. The hydrogen permeation flux (J_H(2)) increases with temperature at the lower temperature range and tends to level off at higher temperatures. At constant temperature, J_H(2) increases with the upstream hydrogen partial pressure and downstream oxygen partial pressure. J_H(2) also increases with decreasing membrane thickness, indicating the bulk diffusion being the rate-limiting step for hydrogen permeation through thick SCTm membranes. J_H(2) as high as 3×10^-8 mol/cm² s was obtained at 900 °C with a 1.6 mm thick SCTm membrane when 10% H₂/He and air were used respectively as the feed and sweeping gases.