The conversion of crystalline metal–organic frameworks (MOFs) into metal compounds/carbon hybrid nanocomposites via pyrolysis provides a promising solution to design electrocatalysts for electrochemical water splitting. However, pyrolyzing MOFs generally involves a complex high‐temperature treatment, which can destroy the coordinated surroundings within MOFs, and as a result not taking their full advantage of their electrolysis properties. Herein, a simple and room‐temperature boronization strategy is developed to convert nickel zeolite imidazolate framework (Ni‐ZIF) nanorods into ultrathin Ni‐ZIF/NiB nanosheets with abundant crystalline–amorphous phase boundaries. The combined experiment, and theoretical calculation results disclose that the ultrathin thickness allows fast electron transfer and ensures increased exposure of surface coordinatively unsaturated active sites while the crystalline–amorphous interface elaborately changes the potential‐determining step to energetically favorable intermediates. As a result, Ni‐ZIF/NiB nanosheets supported on nickel foam (NF) require overpotentials of 67 mV for the hydrogen evolution reaction and 234 mV for the oxygen evolution reaction to achieve a current density of 10 mA cm−2. Remarkably, Ni‐ZIF/NiB@NF as a bifunctional electrocatalyst for overall water splitting enables an alkaline electrolyzer with 10 mA cm−2 at an ultralow cell voltage of 1.54 V. The present work may open a new avenue to the design of MOF‐derived composites for electrocatalysis.

Objective This paper presents an assessment of physical meanings of parameter and goodness of fit for homodyned K (HK) distribution modeling ultrasonic speckles from scatterer distributions with wide-varying spatial organizations. Methods A set of 3D scatterer phantoms based on gamma distributions is built to be implemented from the clustered to random to uniform scatterer distributions continuously. The model parameters are obtained by maximum likelihood estimation (MLE) from statistical histograms of the ultrasonic envelope data and then compared with those by the optimally fitting models chosen from three single distributions. Results show that the parameters of the HK distribution still present their respective physical meanings of independent contributions in the scatterer distributions. Moreover, the HK distribution presents better goodness of fit with a maximum relative MLE difference of 6.23% for random or clustered scatterers with a well-organized periodic structure. Experiments based on ultrasonic envelope data from common carotid arterial B-mode images of human subjects validate the modeling performance of HK distribution. Conclusion We conclude that the HK model for ultrasonic speckles is a better choice for characterizing tissue with a wide variety of spatial organizations, especially the emphasis on the goodness of fit for the tissue in practical applications.

Transition metal dichalcogenides (TMDs) are a class of materials with various useful properties, and it is worthwhile to have a thorough evaluation of the characteristics of the TMDs, most importantly, their structural stability and exfoliability, in a systematic fashion. Here, by employing high-throughput first-principles calculations, we investigate the vast phase space of TMDs, including 16 bulk phases and 6 monolayer phases for all possible transition metal dichalcogenide combinations [comprising (3d, 4d, 5d) transition-metal cations and (S, Se, Te) anions], totaling 1386 compounds. Through the “bird-view” of the as-large-as-possible configurational and chemical space of TMDs, our work presents comprehensive energy landscapes to elucidate the thermodynamic stability as well as the exfoliability of TMDs, which are of vital importance for future synthesis and exploration towards large-scale industrial applications.

The phenomenon of near-field concentration of sound wave plays an important role in harnessing of sound wave in underwater sonar or similar devices, where high pressure field is required. Material parameters for the metamaterial-assisted acoustic concentrators with arbitrary N-sided regular polygonal cross section are derived based on coordination transformation approach. Acoustic intensity enhancement of the concentrator has been shown by full-wave simulation. All theoretical and numerical results validate the generality and effectiveness of the proposed designing method.

No abstract