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.

The local coordination of the manganese in Li[Co

The fusion reactions d + d → t + p and d + d → 3 He + n with both deuteron beams polarized will be studied experimentally by a collaboration between the Institut für Kernphysik of Forschungszentrum Jülich (FZJ), Germany,

The local coordination of the manganese in Li[Co0.98Mn0.02]O2 cathode materials for lithium-ion batteries has been investigated by means of a joint XRD and multifrequency electron paramagnetic resonance (EPR) characterization approach. EPR showed the manganese being in a tetravalent high-spin Mn4+-oxidation state with S=32. The set of spin-Hamiltonian parameters obtained from the multi-frequency EPR analysis with Larmor frequencies ranging between 9.4 and 406 GHz is transformed into structural information by means of the recently introduced Monte-Carlo Newman-superposition modeling. Based on this analysis, the Mn4+ are shown being incorporated for the Co3+-sites, i.e. acting as donor-type functional centers MnCo•. In that respect, for Mn4+ the negative sign of the axial second-order fine-structure interaction parameter B20 is indicative of an elongated oxygen octahedron in its first coordination sphere, whereas B20>0 rather points to a compressed octahedron coordinated about the Mn4+centers. Furthermore, the results obtained here suggest that the oxygen octahedron about the Mn4+-ion is slightly distorted as compared to the CoO6 octahedron. Concerning the coordination to next-nearest neighbor ions, part of the manganese resides in manganese-rich domains, whereas the for the remaining centers the Co3+-site is randomly occupied with Co/Mn according to the effective stoichiometry of the compound. Finally, a structural stability range emerges from the Newman-modeling that supports the discussed ability of manganese to act as an structure-stabilizing element in layered oxides. Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.