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For the quantitative determination of the effective reaction area in an SOFC cathode, a new type of model patterned electrode was proposed and fabricated with La0.6Sr0.4CoO3-δ (LSC). In situ micro X-ray absorption spectroscopy (XAS) measurements were performed in 1 bar of p(O2) at 973 K under open circuit and cathodic polarization. Absorption spectra were taken at different positions with the position resolution of less than 1 μm. The increase in the absorbance, i.e. the decrease in the oxygen potential, was observed near the electrod/electrolyte interface, when the electrode was cathodically polarized. The characteristic length of the effective reaction area for the patterned LSC electrode was estimated approximately 20 μm from the interface. Electrochemical impedance spectroscopy (EIS) measurements were also carried out with the patterned LSC electrode. The characteristic length of the effective reaction area estimated by EIS was close to one by XAS.

Oxygen chemical potential distribution in a porous La0.6Sr0.4CoO3-δ (LSC64) electrode on a Ce0.9Gd0.1CoO1.95- δ (GDC) electrolyte under polarization was evaluated by using in situ X-ray absorption spectroscopy (XAS) at P(O2) = 10-2 bar and 873 K. The application of synchrotron X-ray focused into the submicrometer size enabled us to experimentally clarify the oxygen potential distribution in the vicinity of electrode/electrolyte interface with the position resolution of micrometer. Electrochemical impedance spectroscopy (EIS) measurements, followed by the analysis assuming the transmission line model (TLM) as an equivalent circuit, were performed with the same electrochemical cell for the XAS measurements. Based on the results by in-situ micro XAS and EIS measurements, the effective reaction area in the porous LSC64 electrode was discussed.

The contribution of the triple phase boundary reaction in a mixed ionic and electronic conducting (MIEC) cathode in solid oxide fuel cells (SOFCs) was investigated. For this purpose, patterned thin film electrodes with or without triple phase boundaries, which simplified the microstructure of a practical porous electrode, were proposed and fabricated. In this work, an La 0.6 Sr 0.4 CoO 3-δ (LSC) electrode on a Ce 0.9 Gd 0.1 O 1.95 electrolyte was chosen as a model SOFC MIEC cathode. Effective reaction area was evaluated by means of operando micro X-ray absorption spectroscopy with the model electrodes under 10 -2 bar of p(O 2 ) at 873 K. It was found that the introduction of triple phase boundaries shortened the effective reaction area. The results may indicate the non-negligible contribution of the triple phase boundary reaction even in SOFC MIEC cathodes.

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