To clarify guidelines for a high-performance mixed conducting oxide anode, electrochemical behaviors of mixed conducting oxide anodes were studied on the oxides, La 0.

In order to elucidate the reaction zone in porous normalCe0.9normalGd0.1normalO1.95−δ anodes on yttria-stabilized zirconia (YSZ), ac impedance and steady-state polarization measurements are carried out in normalH2–normalH2O–Ar gas mixtures with different electrode thicknesses, 7, 20, and 45μm anodes. Steady-state polarization current becomes larger as the electrode becomes thicker, while the current per unit surface area shows similar value. Therefore, the current seems to be a function of the electrode surface area. In ac impedance measurements, an extremely large pseudo-capacitance is observed to be as large as 105–106μFcm−2 . The measured pseudo-capacitance is caused by the nonstoichiometric perturbation of the oxygen content in the anode material. Both steady-state polarization and ac impedance measurements suggest that the reaction zone extends from the interface of YSZ/porous normalCe0.9normalGd0.1normalO1.95−δ anodes toward the outer gas phase. The distribution of electrochemically active zone is semiquantitatively estimated. The activity for the surface reaction gradually decreases with increasing the distance from the electrode/electrolyte interface, and the reduction rate of the activity becomes high as the electrode thickness increases.

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The protonic-electronic mixed conductors are of great interest for their potential applications particularly for the hydrogen separation that is essential for hydrogen production from hydrocarbons. This paper deals with the mixed conduction properties of BaCe 0.9Ϫx Y 0.1 Ru x O 3Ϫ␣ (x ϭ 0-0.1) in which Ru is partially substituted for Ce in the high-temperature proton conductor, BaCe 0.9 Y 0.1 O 3Ϫ␣ . Appreciable hydrogen permeation through the Ru-doped materials was observed and is attributed to ambipolar diffusion. The mixed conducting mechanism is discussed in terms of the defect chemistry and electronic structures revealed by the electrochemical and spectroscopic measurements.