Surface reaction controlling hydrogen permeation through lanthanum-doped ceria membrane with asymmetric structure

A thin membrane (thickness = ～10 µm) made of a lanthanum highly-doped cerium oxide (La0.5Ce0.5O2-δ, LDC) was fabricated on a mixed porous layer consisting of Ni and the LDC. Comparing the results of permeation experiments for hydrogen and helium gases confirmed that the asymmetric membrane acted as a mixed protonic and electronic conducting hydrogen separation membrane and that the thin LDC membrane was an almost dense layer. The most striking result of the permeation experiments was that the hydrogen permeation flux increased with increase in the crystal grain boundary length per unit area of the surface and increased in proportion to the square root of hydrogen partial pressure, showing that the flux is controlled by a surface reaction between the adsorbed hydrogen and proton at the crystal grain boundary.