Attempts have been made to develop experimental techniques for obtaining microscopic information on high temperature electrodes under current flow. Several techniques are proposed to investigate the geometrical distribution of the series and parallel processes inside the electrode layer. Based on the local equilibrium concept, the contribution of the series processes were studied by probing the local oxygen potential. A microprobe oxygen sensor was developed to measure the oxygen potential profile on a model electrode of (La,Sr)MnO3 on YSZ. Use of alternative methods that detect the valence state of the cations in the electrode material were also proposed. As an ex-situ technique, active sites for gas-solid oxygen exchange reaction were investigated by using isotope exchange and SIMS (secondary ion mass spectrometry) analysis. The three-dimensional distribution of the isotope ratio was obtained by SIMS with imaging capability. A non-uniform distribution of the reaction rate on the electrode surface was visualized for the electrode material with and without current flow. By the imaging technique, an extraordinary fast oxygen exchange site was found on (La,Sr)(2)CoO4/(La,Sr)CoO3 boundaries. (c) 2006 Elsevier B.V. All rights reserved.