A new insight into the rate determining step of cathodic delamination

One of the most important mechanisms of organic coating degradation is cathodic delamination. Although a significant progress towards the fundamentals of delamination was achieved in the recent decades, the underlying key parameters are not fully understood. It is believed that either cation migration along the delaminated interface or oxygen reduction at the interface are rate determining. However, as will be shown here this is not the case. A new hypothesis, which is cation insertion into the intact interface as the rate determining step in delamination, is proposed using a combined Scanning Kelvin Probe/potentiostat set-up and an in-depth delamination rate analysis. © 2022 The Author

In situ microscopic investigation of ion migration on the surface of chromium coated steels

Cathodic spreading of electrolyte on two-layers chromium coatings electrodeposited from trivalent chromium electrolyte on steel was studied on the micro- and the macroscale. The behavior is discussed in view of results obtained on electrical conductivity as measured by current-sensing atomic force microscopy. The coatings were found to hinder electron transport. Heterogeneities observed in the electrical conductivity are correlated to heterogeneities of the electrolyte spreading behavior, studied using in situ scanning Kelvin probe force microscopy. In average, the kinetics of spreading observed at microscopic scales are similar to that observed using a scanning Kelvin probe at larger scales. The scanning Kelvin probe force microscopy is demonstrated as a robust in situ technique to follow electrolyte spreading and study microscopic defects/heterogeneities on the surface

Limiting Current Density of Oxygen Reduction under Ultrathin Electrolyte Layers: From the Micrometer Range to Monolayers

The oxygen reduction reaction (ORR) under ultrathin electrolyte layers is a key reaction in many processes, from atmospheric corrosion to energy conversion in fuel cells. However, the ORR current under ultrathin electrolyte layers is difficult to measure using conventional electrochemical methods. Hence, reliable data are scarce for the micrometer range and totally missing for the sub-micrometer range of the electrolyte layer thickness. Here, we report a novel hydrogen-permeation-based approach to measure the ORR current underneath thin and ultrathin electrolyte layers. By using a Kelvin-probe-based measurement of the potential, which results from dynamic equilibrium of oxygen reduction and hydrogen oxidation, and the corresponding hydrogen charging current density, the full current-potential relationship can be constructed. The results shed a new light on the nature of the limiting current density of ORR underneath ultrathin layers of electrolyte. © 2021 The Authors. ChemElectroChem published by Wiley-VCH Gmb

Potential control under thin aqueous layers using a Kelvin Probe

Kelvin Probes can be modified to control as well as monitor potential. The design and operation of two different Kelvin Probe Potentiostats (KPPs) are described in this paper. One approach uses a permanent magnet and double coil to oscillate the needle at a fixed frequency, an AC backing potential, and software analysis and control schemes. This technique can also control the distance between the tip and sample, thereby tracking the topography of the sample. Both KPPs were used to make measurements on Type 304L stainless steel under thin layers of electrolyte. Cathodic polarization curves exhibited a limiting current density associated with oxygen reduction. The limiting current density varied with solution layer thickness over a finite range of thickness. Anodic polarization curves on 304L in a thin layer of chloride solution resulted in pitting corrosion. The breakdown potential did not vary with solution layer thickness. However, the thin layer was observed to increase in volume remarkably during pit growth owing to the absorption of water from the high humidity environment into the layer with ionic strength increased by the pit dissolution. The open circuit potential (OCP) and solution layer thickness were monitored during drying out of a thin electrolyte layer. Pitting corrosion initiated, as indicated by a sharp drop in the OCP, as the solution thinned and increased in concentration.This work was supported in part by the Office of Science and Technology and International (OST&I), Office of Civilian Radioactive Waste Management (OCRWM), US Department of Energy (DOE). The work is carried out as part of the DOE Multi-University Corrosion Cooperative under Cooperative Agreement DE-FC28-04RW12252

Deep learning framework for uncovering compositional and environmental contributions to pitting resistance in passivating alloys

We have developed a deep-learning-based framework for understanding the individual and mutually combined contributions of different alloying elements and environmental conditions towards the pitting resistance of corrosion-resistant alloys. A fully connected deep neural network (DNN) was trained on previously published datasets on corrosion-relevant electrochemical metrics, to predict the pitting potential of an alloy, given the chemical composition and environmental conditions. Mean absolute error of 170 mV in the predicted pitting potential, with an R-square coefficient of 0.61 was obtained after training. The trained DNN model was used for multi-dimensional gradient descent optimization to search for conditions maximizing the pitting potential. Among environmental variables, chloride-ion concentration was universally found to be detrimental. Increasing the amounts of dissolved nitrogen/carbon was found to have the strongest beneficial influence in many alloys. Supersaturating transition metal high entropy alloys with large amounts of interstitial nitrogen/carbon has emerged as a possible direction for corrosion-resistant alloy design

Direct growth of graphene on GaN via plasma-enhanced chemical vapor deposition under N₂ atmosphere

One of the bottlenecks in the implementation of graphene as a transparent electrode in modern opto-electronic devices is the need for complicated and damaging transfer processes of high-quality graphene sheets onto the desired target substrates. Here, we study the direct, plasma-enhanced chemical vapor deposition (PECVD) growth of graphene on GaN-based light-emitting diodes (LEDs). By replacing the commonly used hydrogen (H2) process gas with nitrogen (N2), we were able to suppress GaN surface decomposition while simultaneously enabling graphene deposition at lt;800 °C in a single-step growth process. Optimizing the methane (CH4) flow and varying the growth time between 0.5 h and 8 h, the electro-optical properties of the graphene layers could be tuned to sheet resistances as low as ∼1 kΩ/D with a maximum transparency loss of ∼12. The resulting high-quality graphene electrodes show an enhanced current spreading effect and an increase of the emission area by a factor of ∼8 in operating LEDs. © 2020 The Author(s)

Systematic review of interventions for reducing stigma experienced by children with disabilities and their families in low- and middle-income countries: state of the evidence.

OBJECTIVES: To identify and assess the evidence for interventions to reduce stigma experienced by children with disabilities and their families in low- and middle-income settings. METHODS: Systematic review of seven databases (MEDLINE, EMBASE, Global Health, PsycINFO, Social Policy and Practice, CINAHL, IBSS) for studies of interventions that aimed to reduce stigma for children with disabilities published from January 2000 to April 2018. Data were extracted on study population, study design, intervention level(s) and target group, and type(s) of stigma addressed. A narrative approach was used to synthesise the results. RESULTS: Twenty studies were included. The majority (65%) of interventions targeted enacted stigma (negative attitudes) and the most common intervention approach was education/training (63%). Over half (54%) of interventions were delivered at the organisational/institutional level, and only four studies targeted more than one social level. The most common disability targeted was epilepsy (50%) followed by intellectual impairment (20%). The majority of studies (n = 18/20, 90%) found a reduction in a component of stigma; however, most (90%) studies had a high risk of bias. CONCLUSIONS: This review highlights the lack of quality evidence on effective stigma-reduction strategies for children with disabilities. Validation and consistent use of contextually relevant scales to measure stigma may advance this field of research. Studies that involve people with disabilities in the design and implementation of these strategies are needed

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