Optical and electrochemical effects of H₂ and O₂ bubbles at upward-facing Si photoelectrodes

The effects of the size, contact-angle, and coverage of gas bubbles on solar fuels devices were characterized at cm-scale, upward-facing planar and microwire-array Si photoelectrodes in stagnant electrolytes. Experimental measurements were supported by ray-tracing simulations of surface attached gas bubble films. A dilute, redox-active tracer allowed for the quantification of the mass-transport effects of bubble coverage during photoanodic O₂ (g) evolution at upward-facing photoanodes in 1.0 M KOH(aq.). Measurements of the gas coverage at upward-facing p-Si photocathodes in 0.50 M H₂SO₄ (aq.) allowed for the nucleation rate and contact angle of H₂ (g) bubbles to be evaluated for systems having various surface free energies. Under simulated solar illumination, the rapid departure of small O₂ (g) bubbles produced stable photocurrents at upward-facing oxygen-evolving Si photoanodes and yielded increased mass-transport velocities relative to a stagnant electrolyte, indicating that bubbles can provide a net benefit to the photoelectrochemical performance of an upward-facing photoanode in solar fuels devices

Spontaneous Formation of >90% Optically Transmissive, Electrochemically Active CoP Films for Photoelectrochemical Hydrogen Evolution

Earth-abundant catalysts for the hydrogen-evolution reaction require increased mass loadings, relative to Pt films, to achieve comparable activity and stability in acidic electrolytes. We report herein that spontaneous nanostructuring of opaque, electrodeposited CoP films, 40–120 nm in thickness, leads to transparent electrocatalyst films that exhibit up to 90% optical transmission in the visible spectrum. The photocurrent density under simulated sunlight at a representative n+p-Si(100)/CoP photocathode increases by 200% after exposure to 0.50 M H₂SO₄ (aq) and remains stable for 12 h of continuous operation. Atomic force microscopy and scanning electron microscopy of the film before and after exposure to 0.50 M H₂SO₄ (aq) validate an optical model for transparent CoP films as probed with spectroscopic ellipsometry

A-Train Data Depot: Integrating and Exploring Data Along the A-Train Tracks

The immense potential for new science findings as a result of inter-instrument data analysis has led to the development of a new data portal at GSFC: the A-train Data Depot. The power and utility of this new service to the general public is amplified immensely when the archived data are used in conjunction with online data analysis services like Giovanni. This presentation details some of the challenges of data usage from multiple distinct missions and how the tool sets we have developed can help to overcome these challenges, considerably cut down on analysis overhead and promote science exploration in an otherwise very challenging arena

Failure modes of protection layers produced by atomic layer deposition of amorphous TiO₂ on GaAs anodes

Amorphous titanium dioxide (a-TiO₂) films formed by atomic layer deposition can serve as protective coatings for semiconducting photoanodes in water-splitting cells using strongly alkaline aqueous electrolytes. Herein, we experimentally examine the mechanisms of failure for p⁺-GaAs anodes coated with a-TiO₂ films (GaAs/a-TiO₂). Galvanic displacement of exposed GaAs by Au allowed imaging of pinholes in the a-TiO₂ coatings, and enabled collection of quantitative and statistical data associated with pinhole defects. A combination of imaging, electrochemical measurements, and quantitative analyses of corrosion products indicated that extrinsic pinholes were present in the a-TiO₂ films before electrochemical operation. During electrochemical operation these pinholes led to pitting corrosion of the underlying GaAs substrate. The dominant source of pinholes was the presence of atmospheric particulate matter on the GaAs surface during deposition of the a-TiO₂ layer. The pinhole density decreased substantially when the thickness of the a-TiO₂ coating increased beyond 45 nm, and approached zero when the thickness of the film exceeded 112 nm. The density of pinholes in films thinner than 45 nm decreased when the a-TiO₂ coating was deposited in an environmentally controlled cleanroom. Pinhole-free GaAs/a-TiO₂ devices were also tested via chronoamperometry to quantify the rate of pinhole formation during electrochemistry. The time-to-failure increased with thickness, suggesting that the failure mechanism may involve diffusion or migration through the film. However, other mechanisms may also contribute to the degradation of thicker films (>112 nm). Nevertheless, as previously hypothesized, extrinsic pinhole defects formed during deposition and testing control the short-term protective performance of the a-TiO₂ film for GaAs anodes evolving O₂ from water

Noninvasive Evaluation of Neural Impairment in Subjects With Impaired Glucose Tolerance

OBJECTIVE—To evaluate neural dysfunction in subjects with impaired glucose tolerance (IGT)

Adoption of the ADA/EASD guidelines in 10 Eastern and Southern European countries: Physician survey and good clinical practice recommendations from an international expert panel

Aims: Evidence from cardiovascular outcomes trials (CVOTs) of glucagon-like peptide-1 receptor agonists and sodium-glucose cotransporter-2 inhibitors was reflected in the most recent guidelines from the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). The aim of the present study was to assess the adoption of the ADA/EASD guidelines in a convenience sample of physicians from Eastern and Southern Europe, the barriers to the implementation of these guidelines and the measures needed to facilitate their implementation. Methods: Attendees at two international diabetes conferences could volunteer to respond to a fully anonymous survey. Responses were analysed descriptively and a panel of experts from around the region was consulted to interpret the survey results. Results: Responses (n = 96) from 10 countries were analysed. Most participants (63.4%) considered the ADA/EASD guidelines fundamental to their practice. All respondents saw the value of the CVOT-based ADA/EASD recommendations and 77-80% generally implemented them. Measures suggested to improve adherence to the ADA/EASD guidelines included aligning reimbursement policy with the guidelines (54.4%), publishing guidelines in a simple and concise form (42.4%) and translating guidelines into local languages (33.3%). Conclusions: Aligning reimbursement with recent evidence and providing short summaries of the ADA/EASD guidelines in local languages could facilitate physician adherence.(c) 2020 The Author. Published by Elsevier B.V. This is an open access article under the CC BY NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)