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| Hauptseite > Publikationsdatenbank > Degradation Mechanisms in Solid-Oxide Fuel and Electrolyzer Cells: Analytical Description of Nickel Agglomeration in a Ni / Y S Z Electrode |
| Hauptseite > Publikationsdatenbank > Degradation Mechanisms in Solid-Oxide Fuel and Electrolyzer Cells: Analytical Description of Nickel Agglomeration in a Ni / Y S Z Electrode |
| Journal Article | FZJ-2017-03288 |
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2017
American Physical Society
College Park, Md. [u.a.]
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Please use a persistent id in citations: http://hdl.handle.net/2128/14293 doi:10.1103/PhysRevApplied.7.044007
Abstract: The microstructural evolution of a porous electrode consisting of a metal-ceramic matrix, consisting of nickel and yttria-stabilized zirconia (YSZ), is one of the main degradation mechanisms in a solid-oxide cell (SOC), in either fuel cell or electrolyzer mode. In that respect, the agglomeration of nickel particles in a SOC electrode leads to a decrease in the electronic conductivity as well as in the active catalytic area for the oxidation-reduction reaction of the fuel-water steam. An analytical model of the agglomeration behavior of a Ni/YSZ electrode is proposed that allows for a quantitative description of the nickel agglomeration. The accuracy of the model is validated in terms of a comparison with experimental degradation measurements. The model is based on contact probabilities of nickel clusters in a porous network of nickel and YSZ, derived from an algorithm of the agglomeration process. The iterative algorithm is converted into an analytical function, which involves structural parameters of the electrode, such as the porosity and the nickel content. Furthermore, to describe the agglomeration mechanism, the influence of the steam content and the flux rate are taken into account via reactions on the nickel surface. In the next step, the developed agglomeration model is combined with the mechanism of the Ostwald ripening. The calculated grain-size growth is compared to measurements at different temperatures and under low flux rates and low steam content, as well as under high flux rates and high steam content. The results confirm the necessity of connecting the two mechanisms and clarify the circumstances in which the single processes occur and how they contribute to the total agglomeration of the particles in the electrode
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