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Laser fragmentation induced defect‐rich cobalt oxide nanoparticles for electrochemical oxygen evolution reaction
摘要： Sub-5 nm cobalt oxide nanoparticles were produced in a water flowing system by pulsed laser fragmentation in liquid (PLFL). Particle fragmentation from 8 nm to 4 nm was observed and proposed to be induced by the oxidation process in water where oxidative species were present and the local temperature was rapidly elevated under laser irradiation. Significantly higher surface area, crystal phase transformation and formation of structural defects (Co2+ defects and oxygen vacancies) through the PLFL process were evidenced by a detailed structural characterization using nitrogen physisorption, electron microscopy, synchrotron X-ray diffraction and X-ray photoelectron spectroscopy. When employed as electrocatalysts for the oxygen evolution reaction under alkaline conditions, the fragmented cobalt oxides exhibited superior catalytic activity over pristine and nanocasted cobalt oxides, with delivering a current density of 10 mA/cm2 at 369 mV and a Tafel slope of 46 mV/dec, which is attributed to: (i) a larger exposed active surface area, (ii) formation of defects and iii) an increased charge transfer rate. The study provides an effective approach to engineer cobalt oxide nanostructure in a water flowing system, which shows great potential for sustainable production of active cobalt catalysts.
关键词： structural defects,cobalt oxide,nanostructure,Oxygen evolution reaction,laser fragmentation
更新于2025-09-11 14:15:04
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Proton-Coupled Electron Transfer Kinetics for the Photoinduced Generation of a Cobalt(III)-Hydride Complex
摘要： Studying the formation of transition metal hydride complexes via proton-coupled electron transfer is important for developing next-generation molecular catalysts for hydrogen evolution. We report herein the study of stepwise photoinduced reduction and protonation of [CoIICp-(dppe)]+ (Cp = cyclopentadienyl, dppe = 1,2-bis-(diphenylphosphino)ethane) to form the corresponding hydride complex [HCoIIICp(dppe)]+. Reaction intermediates were optically tracked using transient absorption spectroscopy, and a combination of experimental fitting and kinetic simulations was used to determine apparent rate constants for electron transfer and proton transfer with a range of acid sources. A linear free energy relationship is observed between measured apparent proton transfer rate constants and acid strength, but marked differences from previously electrochemically determined protonation rate constants are found. These deviations, which stem from ground-state reactivity present in photochemical experiments, highlight the challenges in comparing mechanistic studies using different techniques.
关键词： kinetic simulations,transient absorption spectroscopy,transition metal hydride complexes,proton-coupled electron transfer,hydrogen evolution
更新于2025-09-11 14:15:04
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Dislocation density-based study of grain refinement induced by laser shock peening
摘要： Laser shock peening (LSP) is an innovative surface processing technique. Grain re?nement induced by LSP has been proved to be feasible to improve the surface properties of materials and prolong the service life of metallic components. The three-dimensional ?nite element model, which incorporates a dislocation density-based constitutive model and the temporal-spatial distribution of laser shock wave, was adopted to simulate the process of grain re?nement induced by LSP. The predicted dislocation cell sizes, dimple fabrications induced by the repetitive LSP of copper are in good agreement with experimental results, which con?rms the validity of the dislocation density-based three-dimensional ?nite element model. The e?ects of laser spot overlap ratio and laser power density (peak laser shock wave pressure) on LSP-induced grain re?nement were investigated in detail based on the numerical simulations of multiple LSP of copper and CP-Ti.
关键词： Laser shock peening,Dislocation density evolution,Cell size,Grain re?nement
更新于2025-09-11 14:15:04
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Optimization of LED Lighting for Clinical Settings
摘要： The advent of the LED light source has promoted the concept of human-centric lighting (HCL). The LED has also been responsible for increases in the electrical e?ciency of lighting systems, coupled with recent improvements in their colour properties. We have found that it is also possible to create a lit environment with enhanced clinical attributes by providing a source spectrum that meets the requirements of the Cyanosis Observation Index (COI). This paper describes the use of a di?erential evolution (DE) algorithm for the spectral design of a mixed LED light source capable of meeting COI recommendations as well as HCL performance criteria.
关键词： differential evolution algorithm,Cyanosis Observation Index,LED lighting,human-centric lighting,spectral design
更新于2025-09-11 14:15:04
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Synthesis and improved photoluminescence of hexagonal crystals of Li <sub/>2</sub> ZrF <sub/>6</sub> :Mn <sup>4+</sup> for warm WLED application
摘要： Engineering compositions, structures, and defects can endow nanomaterials with optimized catalytic properties. Here, we report that cobalt oxide (CoOx) ultrathin nanosheets (UTNS, ～1.6 nm thick) with a large number of oxygen defects and mixed cobalt valences can be obtained through a facile one-step hydrothermal protocol. The large number of oxygen defects make the ultrathin CoOx nanosheet a superior OER catalyst with low overpotentials of 315 and 365 mV at current densities of 50 and 200 mA cm?2, respectively. The stable framework-like architectures of the UTNS further ensure their high OER activity and durability. Our method represents a facile one-step preparation of CoOx nanostructures with tunable compositions, morphologies, and defects, and thus promotes OER properties. This strategy may find its wider applicability in designing active, robust, and easy-to-obtain catalysts for OER and other electrocatalytic systems.
关键词： ultrathin nanosheets,oxygen evolution reaction,electrocatalysis,hydrothermal synthesis,cobalt oxide
更新于2025-09-11 14:15:04
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Cocatalyst-free Plasmonic H <sub/>2</sub> Production over Au/Ta <sub/>2</sub> O <sub/>5</sub> under Irradiation of Visible Light
摘要： Gold (Au)-modi?ed tantalum(V) oxide (Ta2O5) prepared by using a colloid photodeposition method produced H2 without the aid of a cocatalyst under visible light irradiation due to the su?ciently negative potential of electrons injected from Au nanoparticles into the conduction band of Ta2O5 (10.47 V).
关键词： Pt free,Plasmonic photocatalyst,H2 evolution
更新于2025-09-11 14:15:04
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Pyrolysis‐Synthesized g‐C <sub/>3</sub> N <sub/>4</sub> /Nb <sub/>2</sub> O <sub/>5</sub> Nanocomposite for Enhanced Photocatalytic Activity under White LED Light Irradiation
摘要： The design and fabrication of highly active visible-light-driven photocatalysts have been received considerable attention in recent years. However, individual component-based photocatalysts are limited in their use because of the high recombination of photoinduced carriers and poor chemical stability. Herein, the Z-scheme-originated photocatalytic activity of in-situ deposited Nb2O5 NPs on the plane surface of carbon nitride (g-C3N4) nanosheets (i. e. CN-NbO) heterostructures was studied using a simple thermal pyrolysis method. The as-synthesized photocatalysts distinctly manifested efficient white light-emitting diode (LED) irradiation toward organic malachite green (MG) dye degradation and photocatalytic hydrogen generation. The CN-NbO heterostructure showed a faster degradation rate of the MG dye and a higher photocatalytic hydrogen evolution rate. In addition, the plausible Z-scheme photocatalytic mechanism for photocatalytic hydrogen production under LED light irradiation was discussed. Photoelectrochemcial studies showed that the superior photoactivity of CN-NbO heterostructure is mainly a result of the suitable alignment of the band edge positions, which diminish carrier recombination and facilitate efficient interfacial charge transport at their interface. This study provides an ideal method for in-situ fabrication of novel two dimensional/one dimension-based photocatalysts with high activity and stable performance for photocatalytic hydrogen generation.
关键词： Dye degradation,Hydrogen evolution,Nanoparticles,Photocatalyst,LED irradiation,Layered materials
更新于2025-09-11 14:15:04
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Enhanced characteristics of fused silica fibers using laser polishing
摘要： We present a measurement of the mean density pro?le of Ca ii gas around galaxies out to ～200 kpc, traced by Fraunhofer’s H & K absorption lines. The measurement is based on cross-correlating the positions of about one million foreground galaxies at z ～ 0.1 and the ?ux decrements induced in the spectra of about 105 background quasars from the Sloan Digital Sky Survey. This technique allows us to trace the total amount of Ca ii absorption induced by the circumgalactic medium, including absorbers too weak to be detected in individual spectra. We can statistically measure Ca ii rest equivalent widths down to several m?, corresponding to column densities of about 5 × 1010 cm?2. We ?nd that the Ca ii column density distribution follows NCa ii ～ r ?1.4 and the mean Ca ii mass in the halo within 200 kpc is ～5 × 103 M(cid:4), averaged over the foreground galaxy sample with median mass ～1010.3 M(cid:4). This is about an order-of-magnitude larger than the Ca ii mass in the interstellar medium of the Milky Way, suggesting that more than 90% of Ca ii in the universe is in the circum- and inter-galactic environments. Our measurements indicate that the amount of Ca ii in halos is larger for galaxies with higher stellar mass and higher star formation rate. For edge-on galaxies we ?nd Ca ii to be more concentrated along the minor axis, i.e., in the polar direction. This suggests that bipolar out?ows induced by star formation must have played a signi?cant role in producing Ca ii in galaxy halos.
关键词： quasars: absorption lines,galaxies: halos,galaxies: evolution,intergalactic medium
更新于2025-09-11 14:15:04
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Shape-controlled synthesis of golf-like, star-like, urchin-like and flower-like SrTiO3 for highly efficient photocatalytic degradation and H2 production
摘要： As a typical perovskite-type metal oxide, SrTiO3 has emerged as a prospective candidate for many fields. However, the synthesis of SrTiO3 with controlled morphology, high surface area, and enhanced photocatalytic activity are still lacking. Herein, a series of porous SrTiO3 with well-controlled morphologies including assembled nanoparticles (ANPs), golf-like particles (GLPs), star-like microspheres (SLMs), urchin-like microspheres (ULMs), and flower-like microspheres (FLMs) were successfully prepared via an ethylene glycol-water mixed solvothermal route. The ratio of VEG/VH2O play an important role in the shape-evolution during the solvothermal reaction. A comparative study of photocatalytic H2 production and photodegradation was performed, and a possible photocatalysis mechanism of SrTiO3 has been proposed. Significantly, the ULMs and FLMs photocatalysts of SrTiO3 with optimized low Pt loading amount (0.075wt.%) exhibited outstanding H2 production rates (8.21 and 7.29 mmol·g-1·h-1) due to its unique structure of high-surface area and defect-rich surface. The facile and shape-controlled synthesis of varied SrTiO3 structures is believed to be useful for the design and application of perovskite.
关键词： Mesoporous SrTiO3,Oxygen vacancy,Photocatalysis,Controlled-synthesis,Morphology evolution
更新于2025-09-11 14:15:04
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Triple-Shelled Co-VSex Hollow Nanocages as Superior Bifunctional Electrode Materials for Efficient Pt-Free Dye-Sensitized Solar Cells and Hydrogen Evolution Reactions
摘要： Complex nanostructures with distinct spatial architectures and more active sites hold broad prospects in new energy conversion fields. Herein, a facile strategy was carried out to construct triple-shelled Co-VSex nanocages, starting via an ion-exchange process about Co-based zeolitic imidazolate framework-67 (ZIF-67) nanopolyhedrons and VO3?, followed by the formation of triple-shelled Co-VSex hollow nanocages during the process of rising the solvothermal temperature under the assistance of SeO32?. Meanwhile, triple-shelled Co-VSx and yolk-double shell Co-VOx nanocages were fabricated as references by a similar process. Benefiting from the larger surface areas and more electrolyte adsorption sites, the triple-shelled Co-VSex nanocages exhibited excellent electrocatalytic performances when applied as the electrochemical catalysts for dye-sensitized solar cell (DSSC) and hydrogen evolution reaction (HER). More concretely, the DSSC based on Co-VSex counter electrode (CE) showed outstanding power conversion efficiency of 9.68% when Pt counterpart was 8.46%. Moreover, Co-VSex electrocatalyst exhibited prominent HER performance with a low onset overpotential of 40 mV and a small Tafel slope of 39.1 mV dec?1 in acid solution.
关键词： Dye-sensitized solar cells,Hydrogen evolution reactions,Pt-free catalysts,Triple-shelled nanocages,Co-VSex,Bifunctional electrocatalysts
更新于2025-09-11 14:15:04