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The unique mixed conduction aspect has much to be explored for ceramic fuel/steam electrodes suggested for higher chemical stability than cermets in SOFC/SOEC applications. Typical symmetric cell configuration of the thin ceramic electrodes on the electrolytes was shown to be a versatile configuration of the electron‐blocking Hebb–Wagner polarization cell for the characterization of the mass and charge transport in mixed conducting oxides by impedance spectroscopy. The Jamnik–Maier transmission line model for the mixed conductors was generalized by replacing the capacitors with constant‐phase elements to describe the extremely non‐ideal impedance behavior of porous but negligibly catalytic La2Ti2O7 layers at various humidity levels up to 90% in hydrogen at 850 °C. Modeling allowed the deconvolution of the parameter set for the evaluation of chemical diffusivity and non‐stoichiometry as well as partial ionic and electronic conductivity of La2Ti2O7. Electrostatic double layer capacitance was found to be orders of magnitude higher than the theoretical despite the correct oxygen activity dependence, which appears generic and thus requires a theoretical clarification. Overlapping interfacial and chemical capacitance as well as the strongly non‐ideal behavior of the latter are mainly responsible for the less clearly distinguished diffusion‐limited feature of the Hebb–Wagner polarization cell.

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The reliability of solid oxide fuel cells (SOFCs) particularly depends on the high quality of solid oxide electrolytes. The application of thinner electrolytes and multi electrolyte layers requires a more reliable characterization method. Most of the investigations on thin film solid electrolytes have been made for the parallel transport along the interface, which is not however directly related to the fuel cell performance of those electrolytes. In this work an array of ion-blocking metallic Ti/Au microelectrodes with about a 160 µm diameter was applied on top of an ultrathin (1 µm) yttria-stabilized-zirconia/gadolinium-doped-ceria (YSZ/GDC) heterolayer solid electrolyte in a micro-SOFC prepared by PLD as well as an 8-µm thick YSZ layer by screen printing, to study the transport characteristics in the perpendicular direction relevant for fuel cell operation. While the capacitance variation in the electrode area supported the working principle of the measurement technique, other local variations could be related to the quality of the electrolyte layers and deposited electrode points. While the small electrode size and low temperature measurements increaseed the electrolyte resistances enough for the reliable estimation, the impedance spectra appeared to consist of only a large electrode polarization. Modulus representation distinguished two high frequency responses with resistance magnitude differing by orders of magnitude, which can be ascribed to the gadolinium-doped ceria buffer electrolyte layer with a 200 nm thickness and yttria-stabilized zirconia layer of about 1 µm. The major impedance response was attributed to the resistance due to electron hole conduction in GDC due to the ion-blocking top electrodes with activation energy of 0.7 eV. The respective conductivity values were obtained by model analysis using empirical Havriliak-Negami elements and by temperature adjustments with respect to the conductivity of the YSZ layers.

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