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The impedance of anode-supported single cells [ Ni∕8 yttria-stabilized zirconia (YSZ) anode; La0.58Sr0.4Co0.2Fe0.8normalO3−δ cathode; 8YSZ electrolyte; area 1cm2 ] was characterized in a broad measuring range of temperature and air/fuel gas composition. The data has been analyzed by calculating the distribution function of relaxation times (DRTs). DRT computations enabled us to separate five different loss mechanisms occurring inside the cathode and anode without the need of an equivalent circuit. Two processes exhibit a systematic dependency on changes in the oxygen partial pressure of the cathode gas and thus can be attributed to diffusional and electrochemical losses on the cathode side. The remaining three processes are very sensitive to changes in the fuel gas but are not affected by variations of the cathode gas. These resistances are classified as a gas diffusion polarization within the anode–substrate and as an electro-oxidation reaction at the triple-phase boundary, respectively.

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This article presents a literature review and new results on experimental and theoretical investigations of the electrochemistry of solid oxide fuel cell (SOFC) model anodes, focusing on the nickel/yttria-stabilized zirconia (Ni/YSZ) materials system with operation under H(2)/H(2)O atmospheres. Micropatterned model anodes were used for electrochemical characterization under well-defined operating conditions. Structural and chemical integrity was confirmed by ex situ pre-test and post-test microstructural and chemical analysis. Elementary kinetic models of reaction and transport processes were used to assess reaction pathways and rate-determining steps. The comparison of experimental and simulated electrochemical behaviors of pattern anodes shows quantitative agreement over a wide range of operating conditions (p(H(2)) = 8×10(2) - 9×10(4) Pa, p(H(2)O) = 2×10(1) - 6×10(4) Pa, T = 400-800 °C). Previously published experimental data on model anodes show a strong scatter in electrochemical performance. Furthermore, model anodes exhibit a pronounced dynamics on multiple time scales which is not reproduced in state-of-the-art models and which is also not observed in technical cermet anodes. Potential origin of these effects as well as consequences for further steps in model anode and anode model studies are discussed.

Nanoscaled and nanoporous ͑La 0.5 Sr 0.5 ͒CoO 3−␦ ͑LSC͒ thin film cathodes ͑film thickness ranging from 200 to 300 nm, grain and pore size in the range of 50 nm͒ were electrochemically characterized to determine their potential for intermediate and lowtemperature solid oxide fuel cells ͑SOFCs͒. Chemically homogeneous, large area ͑25 cm 2 ͒, and nanoporous LSC thin films were derived from metallorganic precursors ͑metallorganic deposition͒ and deposited on yttria-doped zirconia ͓͑YSZ͒ "design 1"͔ and gadolinia-doped ceria ͓͑GCO͒ "design 2"͔. The area-specific polarization resistance ͑ASR pol ͒ of both designs was evaluated on symmetrical cells with special emphasis on constancy, depending on temperature ͑500-850°C͒ and time by means of electrochemical impedance spectroscopy. For both designs, we report the capability of low polarization resistances, e.g., at 600°C, 146 m⍀ cm 2 ͑LSC/YSZ͒, respectively, 130 m⍀ cm 2 ͑LSC/GCO͒. Oxygen reduction reaction was facilitated by a substantial inner surface area of the porous thin-film cathode, as suggested by the application of Adler's model. Nanoporous LSC thin-film cathodes from this study were compared to alternative design concepts for high-performance porous cathodes and with dense ͑La 0.52 Sr 0.48 ͒͑Co 0.18 Fe 0.82 ͒O 3−␦ thin-film cathodes. Furthermore, the aim of our study was ͑i͒ to find a temperature regime with a perspective for chemical durability of an LSC/YSZ interface. We could prove that at a temperature of 500°C and for 100 h, polarization resistance of the LSC/YSZ interface remains constant, and at unreported low values, which reopens LSC/YSZ for micro-SOFC application; ͑ii͒ to estimate the structural durability of nanoscaled and nanoporous LSC thin-film cathodes. We have been able to demonstrate stable and unreported low polarization resistance for LSC/GCO in the temperature range between 500 and 700°C, which is of technical interest for auxiliary-power-unit application.

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