No abstract

Molybdenum disulfide (MoS2), with its active edge sites, is a proposed alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Recently, the inert basal plane of MoS2 was successfully activated and optimized with excellent intrinsic HER activity by creating and further straining sulfur (S) vacancies. Nevertheless, little is known about the HER kinetics of those S vacancies and the additional effects from elastic tensile strain. Herein, scanning electrochemical microscopy was used to determine the HER kinetic data for both unstrained S vacancies (formal potential Ev0 = −0.53 VAg/AgCl, electron-transfer coefficient αv = 0.4, electron-transfer rate constant kv0 = 2.3 × 10(–4) cm/s) and strained S vacancies (Esv0= −0.53 VAg/AgCl, αsv = 0.4, ksv0 = 1.0 × 10(–3) cm/s) on the basal plane of MoS2 monolayers, and the strained S vacancy has an electron-transfer rate 4 times higher than that of the unstrained S vacancy. This study provides a general platform for measuring the kinetics of two-dimensional material-based catalysts.

No abstract

Three kinds of paramagnetic centers named PA, PB and PC have been found in a silicon-silicon dioxide structure at liquid nitrogen temperature. PA (g=∼2.000, ΔH=∼4 Oe), and PB having anisotropic g-value (g=∼2.000∼2.010, ΔH=∼6 Oe) are in the exide, while PC which also has anisotropic g-value (g=∼2.06∼2.07, ΔH=∼9 Oe) is in the silicon near the Si-SiO2 interface. Distribution of PB is successfully determined that it has the maximum concentration within about 400Å from the interface. PA and PB appear when the silicon is oxidized in dry oxidizing ambient or the Si-SiO2 is cooled from elevated temperatures to room temperature with a cooling speed of about 500°C/sec. PC appears when the Si-SiO2 is heated at elevated temperatures followed by rapid cooling to room temperature or is exposed to the ambient containing an appreciable amount of hydrogen at elevated temperatures such as 1000°C, for 10 min. PB is ascribed to a trivalent silicon \overset\shortmid\underset\shortmid-Si· which has a nonbonding orbital electron in the Si-O network. The mechanisms for the various behaviors of the centers are also discussed in detail.

The global COVID-19 pandemic has changed many aspects of daily lives. Wearing personal protective equipment, especially respirators (face masks), has become common for both the public and medical professionals, proving to be effective in preventing spread of the virus. Nevertheless, a detailed understanding of respirator filtration-layer internal structures and their physical configurations is lacking. Here, we report three-dimensional (3D) internal analysis of N95 filtration layers via X-ray tomography. Using deep learning methods, we uncover how the distribution and diameters of fibers within these layers directly affect contaminant particle filtration. The average porosity of the filter layers is found to be 89.1%. Contaminants are more efficiently captured by denser fiber regions, with fibers <1.8 μm in diameter being particularly effective, presumably because of the stronger electric field gradient on smaller diameter fibers. This study provides critical information for further development of N95-type respirators that combine high efficiency with good breathability.