查看更多>>摘要：? 2022 Elsevier B.V.Developing bifunctional ORR&OER electrocatalysts with high activity and stability is challenging for practical application of rechargeable Zinc air batteries. Herein, an ionic liquid strategy is proposed for construction of FeCo alloys encapsulated in nitrogen-doped carbon as bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). By taking advantages of the unique properties such as solvent effect and low volatility, ionic liquid serves as solvent to disperse metal ions in the precursor preparation and nitrogen-containing carbon source during pyrolysis. The FeCo alloy nanoparticles encapsulated in the N-doped carbon matrix show a homogeneous distribution with average sizes of 50–100 nm. Such a core-shell structure endows the catalyst with both high ORR and OER activity and robust stability in alkaline environments. Especially, the half-wave potential (E1/2) for ORR is 0.86 V and the overpotential (Eover) for OER to reach the 10 mA·cm?2 current density is only 280 mV. Furthermore, the obtained bifunctional electrocatalyst also displays high efficiency and great durability when applied in the rechargeable Zn-air battery. The specific capacity and energy density at the discharge current density of 10 mA·cm?2 reach up to 741.5 mAh·g?1 and 830.1 Wh kg?1, respectively. It's envisioned that this ultra-facile method would be applicable to synthesize highly efficient catalysts for other energy conversion systems.
查看更多>>摘要：? 2022 Elsevier B.V.Accurate and convenient detection of nitrogen dioxide (NO2) in the air, which is harmful to human health, is vital. However, it is difficult for many NO2 detection devices to achieve high sensitivity at room temperature. In this work, we synthesized zeolite-imidazolate-frameworks-8 (ZIF-8) nanoparticles and zinc oxide/reduced graphene oxide (ZnO/rGO) aerogel by low-temperature synthesis and sol-gel method. The aerogel composite materials were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM), Brunaue-Emmette-Teller (BET), and Raman spectroscopy. The gas-sensitive element prepared by the material with the mass ratio ZIF-8 to rGO is 5:1 possesses excellent selectivity and higher sensitivity (3.21) to 100 ppm NO2 at room temperature. Reduced graphene oxide (rGO) provides more gas transmission and diffusion channels for improving sensitivity because of a three-dimensional porous structure. When NO2 is exposed, electrons transfer into p-n heterostructure formed by rGO and ZnO composite to achieve the purpose of sense. In this study, the material preparation method is relatively simple and efficient, which is of profound significance to accurately detect the variation of NO2 concentration in air at room temperature.
查看更多>>摘要：? 2022 Elsevier B.V.NiTi alloys with superelasticity and shape memory effects are currently widely used because of its excellent deformation recovery ability, mechanical strength, and biocompatibility. The Ni50.8Ti49.2 alloy was manufactured by using laser solid forming (LSF) technology with pre-alloyed powder in this work. The microstructure, phase transformation and shape recovery of the deposited alloy were influenced by the parameters used in depositing process. The as-deposited Ni50.8Ti49.2 alloy formed by LSF is columnar crystals epitaxially grown along the deposition direction, with a small amount of equiaxed crystals appear between the deposition layers. Two-step/multi-step martensitic transformation occurs in the deposited Ni50.8Ti49.2 alloy. The martensitic transformation temperature slightly changes with the deposition height, whereas the R transformation temperature basically does not change with the deposition height. In the test of the mechanical properties, sample with a laser power of 1700 W and a scanning rate of 680 mm/min has a compression superelastic recovery as high as 9.5%. Moreover, Ti2Ni precipitated phase and R phase appeared in all samples, but only the precipitated Ti2Ni and R phase in this sample had a certain orientation relationship with the matrix. Shape memory characteristics was also tested by compression deformation, and the maximum recovery strain of shape memory effect is 6.1%, which is obtained in the sample deposited with 1500 W laser power and 480 mm/min scanning rate.
查看更多>>摘要：? 2022 Elsevier B.V.Metal nanoparticles layer (Ag and Cu) derived NiFe2O4 thin ?lms have been synthesized on Pt/Ti/SiO2/Si substrates via a facile chemical solution deposition approach. The influence of metal nanoparticles layer on resistive switching performance of NiFe2O4-based devices has been investigated. The multilayer devices exhibit low power, low Set/Reset voltage, low resistance fluctuation, high ON/OFF ratio, and superior retention performance compared to the majority of reported NiFe2O4-based resistance random access memory devices. Such improvement is ascribed to metal nanoparticles layer providing controllable paths to the growth/fracture of conductive filaments and suppressing the randomness of filaments based on Current transport conduction mechanisms and temperature dependence of resistance analysis. The hybrid metal conducting filaments and oxygen vacancies conducting filaments model has been proposed to clarify the behavior.
查看更多>>摘要：? 2022 Elsevier B.V.The serrated grain boundaries have been proven to improve the creep performance and reduce crack growth rate of polycrystalline nickel-based superalloys. However, a slow cooling rate to form the serrated grain boundaries often results in the coarsening of γ′ precipitates, thereby deteriorating the high temperature strength of the nickel-based superalloys. Hereof, a new heat treatment processing, high temperature pre-precipitation treatment (HTPT), is developed to simultaneously achieve the serrated grain boundaries and fine γ′ precipitates. The effects of HTPT conditions on the microstructure of the powder metallurgy nickel-based superalloys are systematically characterized. Surprisingly, the HTPTed samples possess the serrated grain boundaries and obtain even finer γ′ precipitates than those in air cooled samples. With the increasing of holding time from 10 min to 30 min and 60 min at 1140 ℃ for pre-precipitation, the average size of tertiary γ′ precipitates decreases from 43.9 nm to 34.7 nm and 30.4 nm, and the amplitude of the serrated grain boundaries increases from 0.84 μm to 1.71 μm and 1.87 μm, respectively. On the other hand, the excessively long holding time causes the abnormal growth of the secondary γ′ precipitates and the suitable holding time is considered to be 30 min. The formation of the serrated grain boundary during HTPT is related to the growth of the pre-precipitated γ′ precipitates and the hindering effect on the migration of grain boundaries. Our work demonstrates a new way to control the microstructure of nickel-based superalloys.
查看更多>>摘要：? 2022 Elsevier B.V.CrI3, as a soft van der Waals layered magnetic material, has been widely concerned and explored for its magnetic complexity and tunability. In this work, high quality and large size thin CrI3, V and Mn doped single crystals were prepared by chemical vapor transfer method. A remarkable irreversible Barkhausen effect was observed in CrI3 and CrMn0.06I3, which can be attributed to the low dislocation density that facilitates movement of the domain walls. In addition, the introduction of the doping element Mn allows higher saturation magnetization intensity. Cr0.5V0.5I3 exhibits substantially increased coercivity force and larger magnetocrystalline anisotropy compared to CrI3, while kept similar Curie temperature and good environmental stability. The first principles calculations suggest direct and narrowed band gaps in Cr0.5V0.5I3 and VI3 comparing to CrI3. The smaller band gaps and good hard magnetic property make Cr0.5V0.5I3 an alternative choice to future research of spintronic devices.
查看更多>>摘要：? 2022 Elsevier B.V.Thermodynamic properties and vaporization processes of the Gd2O3-HfO2 and Gd2O3-ZrO2 systems were studied by the Knudsen effusion mass spectrometric method (KEMS). The samples used in the present study were synthesized by sintering of pure oxides. The vapor species over the systems at the temperature 2600 K were GdO, ZrO, HfO, ZrO2, and atomic oxygen. The partial pressures of the vapor species, the component activities, and the excess Gibbs energies were obtained in the binary systems studied. It was illustrated that thermodynamic properties found in both systems had the negative deviations from ideality. The thermodynamic data found in the present study were also discussed using the results of modeling of the component activities based on the generalized lattice theory of associated solutions. Correlations were shown between the observed changes in the thermodynamic behavior of the Gd2O3-HfO2 and Gd2O3-ZrO2 systems and the relative number of bonds formed in the condensed phase when the second coordination sphere was taken into consideration.
查看更多>>摘要：? 2022 Elsevier B.V.Layered lithium-rich manganese-based materials with high voltage stability and high energy density are used to modify the surface of spent LiCoO2 materials (LCO) for designing high-performance Li+-storage structures with high specific capacity and high voltage cycling stability. In this typical regeneration process, Mn2+, Co2+, Ni2+, and Li+ acetates were introduced as raw materials for coating Li1.20Mn0.54Co0.13Ni0.13O2 (LLO) on the surface of spent LCO particles uniformly via a sol-gel method. The structural, morphological, and elemental-chemical-state characterisation results indicate that the recycled LLO@LCO materials exhibit a typical core-shell structure, with a layer-structured-Li1.20Mn0.54Co0.13Ni0.13O2 layer ~ 10 nm thick as the high-voltage-stable-shell and a well-ordered layer-LiCoO2 as the high-capacity-core. As expected, the regenerated LLO@LCO composites show an upgraded Li+-storage performance compared to bare LCO. The optimised LLO@LCO materials show an initial capacity of 197.1 mAh g?1 at 0.1 C, and ~ 95.8% retention after 100 cycles under 3.0–4.5 V at a rate of 1 C. All results indicate that this highly efficient, LLO assisted modification regenerate strategy can be easily extended to regenerate other spent cathodes to synthesise advanced energy storage materials with high voltage cycle stability and high specific capacity.
查看更多>>摘要：? 2022 Elsevier B.V.In recent years, with the rapid development of electronic components industry, higher requirements are put forward for energy storage density and efficiency of pulse power capacitors. In this work, the improved energy storage density and efficiency of (Bi0.5Na0.5)0.7Sr0.3TiO3 (BNST)-based ceramics have been obtained by introducing the Sr0.85Bi0.1ZrO3(SBZ). The addition of SBZ reduced phase transition temperature to about 50 oC, accompanied by relaxation enhancement. A high recoverable energy density (Wrec = 3.53 J/cm3) and energy efficiency (η = 87.15%) were synchronously achieved in 0.875BNST-0.125SBZ ceramic under 270 kV/cm. Moreover, excellent temperature stability (20–120 oC) and frequency stability (5–200 Hz) for energy storage have been achieved at 150 kV/cm. A power density (PD) of 7.32 MW/cm3 and the transitory discharge time (t0.9 = 0.86 μs) were achieved for 0.875BNST-0.125SBZ ceramics under 120 kV/cm. These characteristics indicate that 0.875BNST-0.125SBZ ceramic is expected to be applied in high-power equipment.
查看更多>>摘要：? 2022 Elsevier B.V.Prediction of properties of new compositions will accelerate the material design and development. The current study uses a machine learning framework to predict the microhardness of high entropy alloys. Several feature selection algorithms are used to identify the essential material descriptors. The stability selection algorithm gives optimum material descriptors for the current dataset for the microhardness prediction. Eight different machine learning algorithms are trained and tested for microhardness prediction. The accuracy of prediction improved by reducing the higher-dimensional data to lower dimensions using principal component analysis. The current study shows the testing R2 score of more than 0.89 for XGBoost, Random forest, and Bagging regressor algorithms. Experimental data confirms the applicability of various trained algorithms for property prediction, and for the current study, ANN shows better performance for the new experimental data.
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