查看更多>>摘要：? 2022Graphene is considered as a promising electrode material for supercapacitors due to its large specific surface area, excellent electrical conductivity and so on. In this paper, few-layer graphene is prepared by self-propagating combustion reaction between CO and metal magnesium, using powder MgO as deposition template. Graphene with a high specific surface area of up to 928 m2 g?1 replicates the morphological feature of powder MgO. Raman spectroscopy analysis demonstrates that the graphene layer decreases when the dosage of MgO template is increased. The specific capacitance of as-prepared sample exhibits the highest specific capacitance of 222 F g?1 at the current density of 1 A g?1 in EMI [TFSI] electrolyte. The sample demonstrates a “double high” performance with high specific energy density and high specific power density. A high energy density of 76.3 Wh kg?1 can be achieved at a specific power density of 1.75 kW kg?1, and it can still remain 48.6 Wh kg?1 when the specific power density reaches a high level of 35 kW kg?1.
查看更多>>摘要：? 2022 Elsevier B.V.In this work, copper/reduced graphene oxide (Cu/RGO) mixed powders were produced by using hydrogen-reduction (H2 reduction) with graphene oxide (GO) and copper oxide powders as raw materials. The Cu/RGO composite was sintered through spark plasma sintering (SPS). The effects of RGO content and sintering conditions on the relative density, hardness and electrical conductivity of the composite were investigated. The results show that the GO and copper oxide powder can be reduced via H2 reduction when sintered at 500 °C for 8 h. Moreover, as the content of RGO increases from 0 wt% to 0.67 wt%, the hardness and electrical conductivity increases firstly and then decrease. When the content of RGO is 0.33 wt%, the hardness and electrical conductivity of the composite reach the maximum, i.e., 98.6 HV and 80.5% IACS (International Annealed Copper Standard) respectively. The hardness and electrical conductivity are maximum for the composite sintered at 600 °C for 8 h. Further increase in sintering temperature lowers the properties of the composite. The Cu/RGO composites sintered at 600 °C achieved a relative density of 95.56%, with the high hardness of 193.9 HV and electrical conductivity of 89.8% IACS.
查看更多>>摘要：? 2022 Elsevier B.V.The nickel-based GH3230 (Haynes 230) superalloy is widely used in the aerospace and power industries because of its excellent high-temperature strength and thermal stability. Owing to the crack susceptibility, however, GH3230 alloy offers poor processability processed by the laser powder bed fusion (LPBF) process. This paper systematically studies the processability, microstructure and high-temperature tensile performance of LPBF-fabricated GH3230 material modified by the addition of sub-micrometre TiB2 particles. The results reveal that the addition of TiB2 particles contributed to improving the processability of this alloy during the LPBF process. Also, the microcracking in LPBF-fabricated pure-GH3230 was addressed in the present study by introducing 1 wt% or 2 wt% sub-micrometre TiB2 particles to GH3230 powder. When the addition of TiB2 was up to 3 wt%, however, micro-cracks formed again. The micro-CT results confirmed that micro-cracks were the primary defects in the fabricated pure-GH3230 specimen, while only a limited number of open pores were detected in GH3230–1 wt% TiB2 and GH3230–2 wt% TiB2 specimens. The micro-cracks were categorised to solidification and solid-state cracking in terms of their formation mechanisms and characteristics. The yield-strength values of LPBF-fabricated GH3230–1 wt% TiB2 and GH3230–2 wt% TiB2 at 850 °C were examined to 254 MPa and 311 MPa, respectively, which were 29% and 59% higher than pure-GH3230. Compared to pure-GH3230, the elongation values of GH3230–1 wt% TiB2 and GH3230–2 wt% TiB2 were also significantly improved because of the elimination of micro-cracks. This work provides an effective route to eliminate cracks and to improve mechanical properties for Ni-based superalloys.
查看更多>>摘要：? 2022 Elsevier B.V.Flexible resistive random-access memory (RRAM) has attracted significant attention owing to the strong demand for various flexible electronic memory devices. However, fabricating reliable and flexible RRAM is a significant challenge because of the inherently high thermal sensitivity of plastic substrates. In this study, a high-performance flexible RRAM device was fabricated without deforming a plastic substrate by utilizing a precisely controlled UV laser annealing process. The application of laser annealing in an Al/ZnO/Al flexible RRAM changes the concentration of O Frenkel defect pairs in the ZnO layer and produce a ZnO/Al mixed interface layer with high quality oxygen reservoirs. The higher concentration of O Frenkel defect pairs in the ZnO layer induces electroforming-free process, and the improved characteristics such as crystallinity, morphology, and stoichiometry of the interface area result in stable resistive switching and performance enhancement in the flexible RRAM. The laser-annealed flexible RRAM exhibits a high on/off ratio (~1.07 × 104), high cycling endurance (up to 2.5 ×103 cycles), and low power consumption (4.88 μW in SET state and 1.21 μW in RESET state). Importantly, the performance was maintained at a bending radius of up to 5 mm.
查看更多>>摘要：? 2022 Elsevier B.V.Cobalt ferrite (CoFe2O4) nanoparticles are synthesized by sol-gel method using spent LiCoO2 batteries as raw materials successfully. The CoFe2O4 nanoparticles are subsequently coated with N-doped carbon by the carbonization of polydopamine obtained through self-polymerization of dopamine. The N-doped carbon layers with different thickness does not affect the structure and microstructure of CoFe2O4 and they are coated on the surface of CoFe2O4 nanoparticles confirmed by transmission electron microscopy. CoFe2O4/NC30 exhibited superior electrochemical performance, such as high specific capacity (919.6 mAh/g for initial cycle at 0.1 A/g), excellent cycling performance (662.9 mAh/g after 200 cycles at 0.1 A/g) and rate capability (357.9 mAh/g at 2 A/g) for using as anodes in lithium-ion batteries compared with pristine CoFe2O4 and other CoFe2O4/NC nanocomposites. The improved electrochemical performance could be ascribed to enhanced electrical conductivity and structural stability aroused by the N-doped carbon layers.
查看更多>>摘要：? 2022 Elsevier B.V.The development of high-performance magnetocaloric material is one of the keys to actualize the room-temperature magnetic refrigeration technology. Here the effects and mechanisms of solidification behaviors and microstructures on the magnetocaloric effect (MCE) of AlFe2B2 intermetallics are investigated. The solidification behaviors of AlxFe2B2 (x = 1.0, 1.2, 1.4, 1.6, and 1.8) were regulated via controlling the content of Al element, that is, peritectic reaction for x < 1.4 and direct crystallization for x ≥ 1.4. The magnetic entropy changes under an applied magnetic field of 5 T of AlFe2B2 intermetallics prepared by peritectic reaction can reach 7.2 J kg?1K?1 near room-temperature, which is much larger than that of direct crystallization samples (~5 J kg?1K?1). The reason is attributed to the abrupt change of crystal cells and its effect on the magnetoelastic coupling. The present work provides a new perspective to accurately control the MCE of AlFe2B2 phase, which is beneficial for its further practical application.
查看更多>>摘要：? 2022 Elsevier B.V.Microstructure evolution and strengthening mechanisms of MP159 superalloy during room temperature rolling (RTR) and cryorolling (CR) were studied by using the XRD, EBSD and HRTEM methods. The results suggest that the grains size is finer and the density of dislocations is higher in the CR specimens with the same rolling reduction compared with the RTR specimens. Moreover, the deformation nano-twins and L-C locks can form in the RTR and CR specimens. The strengthening mechanism of the MP159 superalloy during RTR and CR processing is mainly ascribed to the dislocation strengthening, grain refinement strengthening and deformation nano-twins strengthening. After rolling deformation, a higher yield strength (YS) and ultimate tensile strength (UTS) were obtained in the CR specimens. Especially, at the rolling reduction of 48%, the YS and UTS of the CR specimens are 342 MPa and 314 MPa higher than that of the RTR specimens, respectively.
查看更多>>摘要：? 2022 Elsevier B.V.High entropy alloys (HEAs) have been the focus of research as a new class of multi-metal alloys due to their outstanding corrosion resistance, radiation stability, and superior mechanical properties. Unfortunately, there are still limitations in the current research on the characteristics of HEA, which can't satisfy the wide application of HEAs. Therefore, it is critical to focus the research on the functional aspects of HEAs to achieve their maximum potential. It is exciting that the complex surface chemistry and flexibility of HEAs in shaping unique functions, have been proven to be excellent materials for catalysts in recent years. The superior functionality of HEAs has led to a rapidly growing demand for them. In particular, HEAs as electrocatalysts for oxygen evolution reactions (OER) have become a hot spot for research. However, the applicability of the HEA as catalysts is affected by various factors such as elemental composition, preparation method, surface morphology. The limited research work and unclear catalytic mechanism of HEA electrocatalysts result in the widespread high overpotential, which hinders the application of high entropy electrocatalysts. This paper summarizes the morphological engineering, derived compositional engineering, synthetic methods, electrical properties of the HEA and their derivatives, and applicability as catalysts. Moreover, the paper highlights the challenges and perspectives for the development of high entropy electrocatalysts in order to provide valuable guidance for future research on HEA and its derivatives in the field of OER.
查看更多>>摘要：? 2022 Elsevier B.V.The goal of searching for advanced dielectrics with high energy storage properties (ESPTs) is still challenging. Here, novel (Sr0.7?xBaxBi0.2)TiO3 (x = 0–0.10) ceramics were designed to optimize dielectric breakdown and ESPTs to meet the needs of high storing energy. The dielectric behavior, energy storage properties, thermal stability, fatigue endurance, and discharging behavior of the studied ceramics were intensively explored. By replacing Sr2+ with highly polarized Ba2+, lattice distortion is induced to produce relaxation characteristics, which improves the maximum polarization and dielectric breakdown strength of the (Sr0.7?xBaxBi0.2)TiO3 ceramics. The optimal ESPTs can be obtained in the (Sr0.66Ba0.04Bi0.2)TiO3 ceramic with a charge energy density of 1.97 J/cm3 and an efficiency of 86.8% under 290 kV/cm, respectively. Simultaneously, it also shows excellent thermal stability in temperature from 30 °C to 160 °C, good fatigue behavior up to 105 cycles, and a fast discharging speed of 1.8 μs, indicating potential high-performance applications.
查看更多>>摘要：? 2022 Elsevier B.V.Ammonia is an important industrial raw material. To promote the production of ammonia, it is urgent to develop efficient catalysts for nitrogen reduction reactions (NRR). Here, we have reported a novel electrocatalyst: γ-graphyne-like BN sheet-supported single metal atom (M/γBN, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ru) for NRR and studied the effect of Hubbard U correction in single-atom catalysts. The results of adsorption show that Ti/γBN, V/γBN, and Ru/γBN have the best adsorption energy for nitrogen. A detailed analysis of the NRR mechanism indicates that V/γBN has the lowest energy barrier in the rate-determining step when it follows a distal mechanism. Further analysis shows that the superior catalytic performance in V/γBN sheet is mainly attributed to the electron donation and back-donation mechanism. More interestingly, V/γBN greatly inhibited HER selectivity. By analyzing the doping structure and adsorption system, it can be found that when considering Hubbard U correction, there will be an obvious correlation between energy and distance. This study not only provides a basis for understanding the mechanism of nitrogen reduction reaction catalyzed by single-atom catalysts but also provides a new design idea for the rational design of high-efficiency NRR catalysts.
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