Two-Dimensional Modelling and Validation of the Mass Flow in a Mixing Stirred Reactor

The present work focuses on the computational modelling of fluid flow in a mixing stirred reactor to describe the flow pattern in two‐dimensional (2D) detail, which can be useful for optimizing the parameters of electroplating for the production of a uniform film on metallic particles in a stirred electrolytic cell. The results of modelling and simulation show that the electrolytic cell geometry and the presence of a solid electrode affect the streamline distribution. The most important parameter affecting the fluid flow is not just the position but also the size of the stirrer as well. It is concluded that the “high cell” with the “big stirrer” can be used for the electroplating of iron micro‐ and nanoparticles in the presence of the cylindrical electrode

The model case of an oxygen storage catalyst - non-stoichiometry, point defects and electrical conductivity of single crystalline CeO2-ZrO2-Y2O3 solid solutions

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The ternary solid solution CeO2–ZrO2 is known for its superior performance as an oxygen storage catalyst in exhaust gas catalysis (e.g. TWC), although the defect chemical background of these outstanding properties is not fully understood quantitatively. Here, a comprehensive experimental study is reported regarding defects and defect-related transport properties of cubic stabilized single crystalline (CexZr1−x)0.8Y0.2O1.9−δ (0 ≤ x ≤ 1) solid solutions as a model system for CeO2–ZrO2. The constant fraction of yttria was chosen in order to fix a defined concentration of oxygen vacancies and to stabilize the cubic fluorite-type lattice for all Ce/Zr ratios. Measurements of the total electrical conductivity, the partial electronic conductivity, the ionic transference number and the non-stoichiometry (oxygen deficiency, oxygen storage capacity) were performed in the oxygen partial pressure range −25 < lg pO2/bar < 0 and for temperatures between 500 °C and 750 °C. The total conductivity at low pO2 is dominated by electronic transport. A strong deviation from the widely accepted ideal solution based point defect model was observed. An extended point defect model was developed using defect activities rather than concentrations in order to describe the point defect reactions in CeO2–ZrO2–Y2O3 properly. It served to obtain good quantitative agreement with the measured data. By a combination of values for non-stoichiometries and for electronic conductivities, the electron mobility could be calculated as a function of pO2, ranging between 10−2 cm2 V−1 s−1 and 10−5 cm2 V−1 s−1. Finally, the origin of the high oxygen storage capacity and superior catalytic promotion performance at a specific ratio of n(Ce)/n(Zr) ≈ 1 was attributed to two main factors: (1) a strongly enhanced electronic conductivity in the high and medium pO2 range qualifies the material to be a good mixed conductor, which is essential for a fast oxygen exchange and (2) the equilibrium constant for the reduction exhibits a maximum, which means that the reduction is thermodynamically most favoured just at this composition

Improved Route to Linear Triblock Copolymers by Coupling with Glycidyl Ether-Activated Poly(ethylene oxide) Chains

Poly(ethylene oxide) block copolymers (PEO$_z$ BCP) have been demonstrated to exhibit remarkably high lithium ion (Li$^+$) conductivity for Li$^+$ batteries applications. For linear poly(isoprene)-b-poly(styrene)-b-poly(ethylene oxide) triblock copolymers (PI$_x$PS$_y$PEO$_z$), a pronounced maximum ion conductivity was reported for short PEO$_z$ molecular weights around 2 kg mol$^{−1}$. To later enable a systematic exploration of the influence of the PI$_x$ and PS$_y$ block lengths and related morphologies on the ion conductivity, a synthetic method is needed where the short PEO$_z$ block length can be kept constant, while the PI$_x$ and PS$_y$ block lengths could be systematically and independently varied. Here, we introduce a glycidyl ether route that allows covalent attachment of pre-synthesized glycidyl-end functionalized PEO$_z$ chains to terminate PI$_x$PS$_y$ BCPs. The attachment proceeds to full conversion in a simplified and reproducible one-pot polymerization such that PI$_x$PS$_y$PEO$_z$ with narrow chain length distribution and a fixed PEO$_z$ block length of z = 1.9 kg mol$^{−1}$ and a Đ = 1.03 are obtained. The successful quantitative end group modification of the PEO$_z$ block was verified by nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). We demonstrate further that with a controlled casting process, ordered microphases with macroscopic long-range directional order can be fabricated, as demonstrated by small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has already been shown in a patent, published by us, that BCPs from the synthesis method presented here exhibit comparable or even higher ionic conductivities than those previously published. Therefore, this PEO$_z$ BCP system is ideally suitable to relate BCP morphology, order and orientation to macroscopic Li$^+$ conductivity in Li$^+$ batteries

Electrochemical characteristics of grain boundaries in gadolinium and aluminum co-doped ceria and ceria-alumina composites

The influence of 1, 2, 4 and 10 cat.% Al2O3 addition on the electrochemical characteristics of commercially available 10 cat.% Gd-doped ceria and a 1:1 cat.% mixture of CeO2:Al2O3 were evaluated in our study. Analysis of the electronic conductivity and polarization-relaxation behavior of the samples showed that an Ohmic contribution to the total electronic resistance cannot only be attributed to the electrode contact resistance but is a combined contribution from the electrode interface and decreased pO2 dependence of the grain boundary resistivity of the material. The average electrical potential barrier at the grain boundaries was calculated from impedance spectroscopy data at 50–300 °C. Kelvin probe force microscopy (KPFM) measurements were used to analyze the local Volta potential distribution at the grain boundaries of pure Ce0.9Gd0.1O1.95 and of samples with 4 and 10 cat.% Al addition at room temperature. KPFM measurements showed clear evidence for an increased Volta potential difference between bulk and grain boundary cores and for a considerable broadening of the Volta potential gradient at the grain boundaries with increasing Al concentration