Proton exchange membrane fuel cells (PEMFCs) with high efficiency and nonpollution characteristics have attracted massive attention from both academic and industrial communities due to their ...irreplaceable roles in building the future sustainable energy system. However, the stability issue of Pt‐based catalysts for oxygen reduction reaction (ORR) has become a central constraint to the widespread deployment of the devices relative to the catalytic activity. This review aims to provide comprehensive insights into how to improve the stability of Pt‐based catalysts for ORR. First, the basic physical chemistry behind the catalyst degradation, including the fundamental understandings of carbon corrosion, catalyst dissolution, and particle sintering, is highlighted. After a discussion of advanced characterization techniques for the catalyst degradation, the design strategies for improving the stability of Pt‐based catalysts are summarized. Finally, further insights into the remaining challenges and future research directions are also provided.
Strategies to improve the stability of Pt‐based catalysts for the oxygen reduction reaction are comprehensively reviewed. The basic physical chemistry behind the catalyst degradation is highlighted. After a discussion of advanced characterization techniques for the catalyst degradation, design strategies for improving the stability of Pt‐based catalysts are proposed.
Atomically ordered intermetallic nanoparticles exhibit improved catalytic activity and durability relative to random alloy counterparts. However, conventional methods with time‐consuming and ...high‐temperature syntheses only have rudimentary capability in controlling the structure of intermetallic nanoparticles, hindering advances of intermetallic nanocatalysts. We report a template‐directed strategy for rapid synthesis of Pd‐based (PdM, M=Pb, Sn and Cd) ultrathin porous intermetallic nanosheets (UPINs) with tunable sizes. This strategy uses preformed seeds, which act as the template to control the deposition of foreign atoms and the subsequent interatomic diffusion. Using the oxygen reduction reaction (ORR) as a model reaction, the as‐synthesized Pd3Pb UPINs exhibit superior activity, durability, and methanol tolerance. The favored geometrical structure and interatomic interaction between Pd and Pb in Pd3Pb UPINs are concluded to account for the enhanced ORR performance.
This template‐directed synthetic strategy is a universal route for shape‐controlled synthesis of intermetallic nanocrystals and will provide new opportunities for intermetallic nanocatalysts.
Highlights
Integration of solar cells, BSHs, and LEDs was developed for energy conversion, storage, and utilization in one system.
NiCo
2
O
4
//AC BSHs were charged by a-Si/H solar cells for stably ...driving LEDs showing high performances.
An integrated system has been provided with a-Si/H solar cells as energy conversion device, NiCo
2
O
4
battery-supercapacitor hybrid (BSH) as energy storage device, and light emitting diodes (LEDs) as energy utilization device. By designing three-dimensional hierarchical NiCo
2
O
4
arrays as faradic electrode, with capacitive electrode of active carbon (AC), BSHs were assembled with energy density of 16.6 Wh kg
–1
, power density of 7285 W kg
–1
, long-term stability with 100% retention after 15,000 cycles, and rather low self-discharge. The NiCo
2
O
4
//AC BSH was charged to 1.6 V in 1 s by solar cells and acted as reliable sources for powering LEDs. The integrated system is rational for operation, having an overall efficiency of 8.1% with storage efficiency of 74.24%. The integrated system demonstrates a stable solar power conversion, outstanding energy storage behavior, and reliable light emitting. Our study offers a precious strategy to design a self-driven integrated system for highly efficient energy utilization.
Purpose
Coronary artery segmentation in coronary computed tomography angiography (CTA) images plays a crucial role in diagnosing cardiovascular diseases. However, due to the complexity of coronary ...CTA images and coronary structure, it is difficult to automatically segment coronary arteries accurately and efficiently from numerous coronary CTA images.
Method
In this study, an automatic method based on symmetrical radiation filter (SRF) and D-means is presented. The SRF, which is applied to the three orthogonal planes, is designed to filter the suspicious vessel tissue according to the features of gradient changes on vascular boundaries to segment coronary arteries accurately and reduce computational cost. Additionally, the D-means local clustering is proposed to be embedded into vessel segmentation to eliminate noise impact in coronary CTA images.
Results
The results of the proposed method were compared against the manual delineations in 210 coronary CTA data sets. The average values of true positive, false positive, Jaccard measure, and Dice coefficient were
0.9541
±
0.0651
,
0.0812
±
0.1024
,
0.8894
±
0.1214
, and
0.9318
±
0.0833
, respectively. Moreover, comparing the delineated data sets and public data sets showed that the proposed method is better than the related methods.
Conclusion
The experimental results indicate that the proposed method can perform complete, robust, and accurate segmentation of coronary arteries with low computational cost. Therefore, the proposed method is proven effective in vessel segmentation of coronary CTA images without extensive training data and can meet clinical applications.
The aim of the present study was to investigate the role and mechanism of microRNA-204-5p (miR-204-5p) in atherosclerosis (AS)-related abnormal human vascular smooth muscle cells (hVSMCs) function. ...Firstly, we analyzed the expression of miR-204-5p and found that the miR-204-5p expression level was clearly downregulated in atherosclerotic plaque tissues and blood samples compared to the normal controls. Then, matrix metallopeptidase-9 (MMP-9) was predicted to be the potential target of miR-204-5p by TargetScan and this prediction was confirmed by luciferase assays. Besides, we observed that miR-204-5p could negatively regulate the expression of MMP-9 in hVSMCs. Subsequently, Thiazolyl Blue Tetrazolium Bromide (MTT) assay, transwell assay and flow cytometry were performed to detect the proliferation, migration and apoptosis of hVSMCs. Down-expression of miR-204-5p led to the promotion of proliferation and migration accompanied with the suppression of apoptosis in hVSMCs, and these effects were reversed by MMP-9-siRNA. In addition, overexpressed miR-204-5p could inhibit hVSMC proliferation and migration and promote the apoptosis of hVSMCs. However, the effects were also abrogated by overexpressed MMP-9. Together, our findings showed that miR-204-5p plays an important role in the growth and migration of hVSMCs by targeting MMP-9, which might be a novel biomarker and promising therapeutic target for AS.
This paper presents an investigation on the synthesis and characterization of ZnO–Ag core–shell nanocomposites. ZnO nanorods were employed as core material for Ag seeds, and subsequent nucleation and ...growth of reduced Ag by formaldehyde formed the ZnO–Ag core–shell nanocomposites. The ZnO–Ag nanocomposites were annealed at different temperature to improve the crystallinity and binding strength of Ag nanoparticles. The morphology, microstructure and optical properties of the ZnO–Ag core–shell nanocomposites were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, ultraviolet–visible (UV–vis) absorption and photoluminescence measurement. It was demonstrated that very small face-center-cubic Ag nanoparticles were coated on the surface of ZnO nanorods. The ultraviolet absorption and surface plasmon absorption band of ZnO–Ag core–shell nanocomposites exhibited some redshifts relative to pure ZnO nanorods and monometallic Ag nanoparticles. The coating of Ag nanocrystals onto the ZnO nanorods completely quenched the photoluminescence. These observations reflected the strong interfacial interaction between ZnO nanorods and Ag nanoparticles. The effect of Ag coating thickness on the morphology and optical properties of ZnO–Ag core–shell nanocomposites was also investigated. Moreover, the growth mechanism of ZnO–Ag core–shell nanocomposites was also proposed and discussed in detail.
Texture surfaces of ZnO:Al (AZO) films are prepared by ammonium acetate, a neutral etching agent. The structural, optical, and electrical properties of AZO films are investigated in detail for ...improving the light trapping ability. Under the optimal etching conditions (e.g., solution concentration of 5.0wt% and etching time of 20min), AZO films have a typical crater-like structure with haze values in the 20–30% range, as well as a high visible transparence and electrical conductivity. A feasible mechanism model is proposed to explain the etching process. Both H+ and OH− hydrolyzed in solution are involved in the etching reaction. The etching reaction and product diffusion co-dominate the process to form crater-like structures. In ammonium acetate, the etching process is much mild and controllable, making it easy to generate homogeneous texture morphologies in a large area. The high conversion efficiency of 10.75% is achieved for single-junction amorphous silicon thin-film solar cells using textured AZO films as the front contact layers. The ammonium acetate is an ideal etchant for preparing textured AZO films for commercial applications in solar cells.
•A novel neutral etchant (CH3COONH4) has been applied to tailor the AZO films.•The etching process is controllable and feasible to fabricate texture surface.•Strong etching pits (50–400nm, 59.5nm RMS) are generated at 5.0wt% for 20min.•High efficiency of 10.75% (AZO cell) is obtained compared to the FTO device (8.65%).
•Builds two databases containing 24,442 data points from 161 sources.•Proposes accurate general model for saturated flow boiling heat transfer.•New correlation predicts the two databases with ...MAD=4.5%.•New correlation is applicable to various channel sizes and flow directions.•New correlation is applicable to both pre-dryout and post-dryout regimes.
A general correlation for heat transfer coefficients of saturated flow boiling is developed based on the first experimental database consisting of 17,778 data points from 101 sources and 13 different fluids. The new correlation makes a significant breakthrough in the prediction accuracy for saturated flow boiling heat transfer, achieving a mean absolute deviation (MAD) of 4.5% against the database, with 68.1% and 89.7% of the data falling within ±5% and ±10% error bands, respectively. The new correlation is validated and compared with 45 existing correlations on the base of the second database of saturated flow boiling heat transfer. The second database contains 6664 data points from 60 sources and 18 different fluids and has no duplicate data from the first. The validation results show that the new correlation has an MAD of 4.4% against the second database, with 69.0% and 93.5% of the data within ±5% and ±10% error bands respectively, further confirming its superior prediction accuracy and reliability. The best existing correlation for the second database, meanwhile, has an MAD of 26.0%, with only 13.0% and 26.0% of the data falling within ±5% and ±10% error bands, respectively. The new correlation is applicable to various channel sizes, flow directions, and flow regimes.
Advancing the development of electrocatalytic CO2 reduction reaction (CO2RR) to address the environmental issues caused by excessive consumption of fossil fuels requires rational design of remarkable ...electrocatalysts, where the identification of active sites and further understanding of structure–performance relationship are the bases. However, the notable dynamic evolution often appears on the catalysts, with typical examples of Cu‐based catalysts, under operating conditions, causing great difficulty in identifying the real active sites and further understanding the correlations between structure and catalytic property. In this context, understanding the dynamic evolution process of catalytically active sites during CO2RR is of particular importance, which inspires to organize the present review. Herein, the fundamental principles of dynamic evolution in CO2RR including thermodynamics and kinetics aspects, followed by the introduction of operando techniques employed to probe the evolution under operating conditions are first highlighted. The dynamic evolution behaviors, involving atomic rearrangement and change in chemical state, on typical catalysts are further discussed, with emphasis on the correlations between evolution behaviors and catalytic properties (activity, selectivity, and stability). The emerging CO2 pulsed electrolysis technique that behaves promise to manipulate the dynamic evolution and future opportunities are finally discussed.
This review summarizes the recent progresses on dynamic evolution of active sites, a significant topic for designing advanced catalysts, in electrocatalytic CO2 reduction reaction (CO2RR), which covers the fundamental principles, operando techniques, the detailed evolution behaviors on typical catalysts with emphasis on real‐time structure–performance relationship, and promising methods to manipulate dynamic process toward specific purpose.
We develop a facile one-step hydrothermal method to directly grow interconnected Co0.85Se nanosheets on nickel foam as electrode for supercapacitors. The Co0.85Se electrodes exhibit a high specific ...capacitance (1528 F g-1 at 1 A g-1 and 715 F g-1 at 20 A g-1), excellent cycling stability (92% retention after 5000 cycles) and good conductivity. Moreover, an asymmetric supercapacitor (ASC) is fabricated using Co0.85Se nanosheets as the positive electrode and active carbon (AC) as the negative electrode. The ASC also exhibits excellent electrochemical performance with high energy density (∼45 Wh kg−1), high power density (16 kW kg-1) and remarkable cycling stability (∼10.9% loss after 5000 cycles). Furthermore, two ASCs connected in series are capable of lighting a red LED at least for 5 min after being charged for only 15 s to 3.2 V. This work demonstrates that the interconnected Co0.85Se nanosheets with three-dimensional porous structures are promising electrodes for high-performance supercapacitors with large energy density.
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•Interconnected Co0.85Se nanosheets have been grown on nickel foam directly.•High specific capacitance and excellent cycling stability have been achieved.•An asymmetric supercapacitor cell has been assembled.•The ASC delivers superior electrochemical performance with high energy density.
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