Mixed ionic-electronic conducting La0.7Sr0.3Cu0.2Fe0.8O3-δ (LSCF7328) oxygen separation membranes are proposed for hydrogen production by water splitting because of their good electrocatalytic activity with a wide range of chemical stability. The properties of hydrogen production by water splitting and the isothermal expansion properties of LSCF7328 were measured as a function of temperature, CO content as a reducing agent, and water vapor pressure. The average expansion coefficient was about 13 × 10-6 K-1 below 973 K, corresponding to thermal expansion, and about 20 × 10-6K-1 between 1073 K and 1273 K, corresponding to a combination of thermal and chemical expansion. Both the chemical diffusivity of oxygen and the surface exchange kinetics were successfully extracted from the transient chemical expansion relaxation profile using Fick's second law. The activation energy for oxygen ionic conductivity was calculated from the Nernst-Einstein equation as 1.31 eV.

Keywords: Water splitting, Chemical expansion, Ionic conductivity