Kelvin Probe Techniques for mapping effective local hydrogen activity and permeation rates

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Cathodic driven coating delamination suppressed by inhibition of cation migration along Zn|polymer interface in atmospheric CO2

International audienceThe degradation of the Zn|polymer interface is inhibited by CO 2 gas in a humid environment. The inhibition mechanism varies greatly for different polymer matrices and depends on the affinity of the polymer to CO 2. Coatings based on polymers with high affinity to CO 2 such as polyacrylamide show high delamination rates due to the fast uptake of water. In this case, the cation transport that causes the initial pull down of potential for initiating the oxygen reduction reaction occurs via the polymer. Here CO 2 decreases water uptake due to competitive absorption into the polymer matrix, inhibiting the delamination rate. CO 2 can quickly reach the interface of polymers with functional groups with a low affinity to water and CO 2 , such as polyvinyl butyral and polyvinyl alcohol. In this case, the inhibition of the delamination rate is achieved by a strong decrease in cation migration rate at the Zn| polymer interface accompanied by the formation of mixed hydrozincite/absorbed CO 2 layers on the ZnO surface underneath the polymers. Further experiments showed that the presence of CO 2 accelerates anion migration, suggesting an influence of CO 2 on the surface charge at the Zn|coating interface, thus affecting ion migration. Inhibition of cation migration has never been reported before and should be taken into account into the mechanism of cathodic-driven delamination on Zn under atmospheric conditions

Mobility of charge carriers in self-assembled monolayers

We present a new approach to study charge transport within 2D layers of organic semi-conductors (OSCs) using atomic force microscopy (AFM)-based lithography applied to self-assembled monolayers (SAMs), fabricated from appropriate organothiols. The extent of lateral charge transport was investigated by insulating pre-defined patches within OSC-based SAMs with regions of insulating SAM made from large band gap alkanethiolates. The new method is demonstrated using a phenyl-linked anthracenethiolate (PAT), 4-(anthracene-2-ylethynyl)benzyl thiolate. I-V characteristics of differently shaped PAT-islands were measured using the AFM tip as a top electrode. We were able to determine a relationship between island size and electrical conductivity, and from this dependence, we could obtain information on the lateral charge transport and charge carrier mobility within the thin OSC layers. Our study demonstrates that AFM nanografting of appropriately functionalized OSC molecules provides a suitable method to determine intrinsic mobilities of charge carriers in OSC thin films. In particular, this method is rather insensitive with regard to influence of grain boundaries and other defects, which hamper the application of conventional methods for the determination of mobilities in macroscopic samples. © 2019 Fu et al

Stable and Active Oxygen Reduction Catalysts with Reduced Noble Metal Loadings through Potential Triggered Support Passivation

The development of stable, cost‐efficient and active materials is one of the main challenges in catalysis. The utilization of platinum in the electroreduction of oxygen is a salient example where the development of new material combinations has led to a drastic increase in specific activity compared to bare platinum. These material classes comprise nanostructured thin films, platinum alloys, shape‐controlled nanostructures and core–shell architectures. Excessive platinum substitution, however, leads to structural and catalytic instabilities. Herein, we introduce a catalyst concept that comprises the use of an atomically thin platinum film deposited on a potential‐triggered passivating support. The model catalyst exhibits an equal specific activity with higher atom utilization compared to bulk platinum. By using potential‐triggered passivation of titanium carbide, irregularities in the Pt film heal out via the formation of insoluble oxide species at the solid/liquid interface. The adaptation of the described catalyst design to the nanoscale and to high‐surface‐area structures highlight the potential for stable, passivating catalyst systems for various electrocatalytic reactions such as the oxygen reduction reaction

Numerical simulation of high temperature corrosion processes in Mn, Cr, Si, Al – alloyed steel samples

The grain boundary oxidation mechanism in hot rolled steel samples during cooling from 500 °C – 800 °C down to room temperature was mathematically modeled. Given a fixed temperature ramp, the migration of the atomic species (iron, oxygen and the alloying elements) has been calculated with the parabolic rate equation for diffusion. After each small time step, the data was transferred into the database ChemApp (GTT-Technologies, Germany) to calculate the oxide composition for each point in thermodynamic equilibrium. The concentrations for each phase were illustrated in a phase map, similar to a cross section polish of the respective specimen. Total element concentration is shown as height plot to better pronounce the increased amount of oxidic phases along the grain boundaries. The obtained results are in good agreement with experimental data for low alloyed steel samples

Kopplung von diffusion und thermodynamik : am Beispiel des Gasnitrierens

Due to the excellent properties of nitrided steels, this technique is of great interest for numerous industrial applications. Hence its development made great progress within the last decades and among different process variations, gas nitriding is frequently used for a wide range of steel grades