查看更多>>摘要：Enhancing the activity of Co-based electrocatalysts can be generally achieved by increasing the active center conductivity even fabricating hybrid materials for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) process. Herein, we developed a bifunctional oxygen electrocatalyst for Zn-air batteries (ZABs). The Ce-doped Co_3O_4 nanoparticles embedded on carbon nanofibers complex catalyst (Ce@Co_3O_4/ CNFs) was synthesized via the incorporation of the electrospinning technology and in-situ growth process. The Ce@Co_3O_4/CNFs exhibited the comparable performance to Pt/C and RuO_2 in the alkaline environment with a half-wave potential of 0.810 V and overpotential of 380 mV(@ 10 mA cm~(-2)) for the ORR and OER, respectively. Moreover, an all-solid-state rechargeable ZABs with Ce@Co_3O_4/CNFs cathode was also assembled, which shows a relatively narrow discharge-charge voltage gap and a good cycle performance. These results provide a novel approach in developing Co-based dual functional electrocatalysts to enable the energy applications.
查看更多>>摘要：The chemical disorder in magnetic shape memory alloys it is an important parameter that impacts on its magneto-mechanical and electronic properties. In this work, Ni_2MnGa thin films were deposited on flexible glass substrates by using DC magnetron sputtering technique. The short-range order/disorder was investigated by means of Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) measurements using at Mn K-edge. Polycrystalline samples of Ni_2MnGa with fixed stoichiometry exhibit 121 structure with low residual stress and similar grain sizes. A phenomenological model taking into account three chemical order parameters associated with main chemical anti-site disorders and reliable lattice tetragonal distortions extracted from X-ray diffraction analyses was used to perform systematic computational simulations. The results reveal the persistence of local tetragonal distortions of the crystal structure with L21 structure under when increasing annealing temperatures that are accompanied by a systematic decrease of the anti-site disorder between Ni and Mn atoms and substitutions between Ni and Ga atoms, with the orderly occupation of the atomic sites of Mn and Ga remaining unstable. This work also shows presents a consistent model to perform quantitative analyses of the chemical anti-site disorders through EXAFS measurements in the on Ni_2MnGa polycrystalline thin films that preserve both the stoichiometry and the L2_1 crystalline structure.
查看更多>>摘要：Nickel-copper-zinc (NiCuZn) ferrites with high permeability and low magnetic loss have high application potential in high-frequency electronics. In this work, NiCuZn ferrite samples with different Cu contents were prepared by a two-step sintering method. First, the optimal temperatures of the two-step sintering method (1025/925 °C) were confirmed, thereafter the influence of the Cu content on the crystal structure, microstructure, magnetic and dielectric properties of NiCuZn ferrite were studied in detail. Structural characterization showed that an increase in Cu content promoted grain growth and resulted in NiCuZn ferrites with a denser microstructure and decreased porosity. However, a second phase of CuO formed once the content of Cu (x value) reached 0.16. The magnetic hysteresis loops revealed that the saturation magnetization increased as x increased and the highest value of 57.3 emu/g was obtained at x = 0.14. The dielectric property measurement showed that increasing the Cu content could improve the dielectric constant and reduce the dielectric loss. The permeability measurements showed an increase in permeability with Cu content from x = 0.10 to x = 0.14 and a decrease when x = 0.16. Consequently, a NiCuZn ferrite with an appropriate microstructure and with high permeability (μ'=855), low magnetic loss (tanδ_μ = 0.02), and high saturation magnetization (57.3 emu/g) could be obtained at a Cu content of x = 0.14 and sintering temperatures of 1025/925 °C in the two-step sintering method. This NiCuZn ferrite provides new guidance for developing RF frequency multilayer inductors.
查看更多>>摘要：In this study, the effect of Sc content on the phase transformation of the 2519 alloy during solidification is investigated through microstructure characterization and thermodynamic calculations. The results show that the grain size of the 0.3-0.4Sc alloy is reduced by 70% (approximately 28.9 um) to achieve maximum refinement in the as-cast 2519(Sc) Al alloy. The phase diagram calculation shows that the sequence of intermetallic formation during the solidification of 2519(Sc) Al alloy is as follows: Al_3Sc, W phase, θ. The primary Al_3Sc particles appear at the center of the a-Al grains and evidently acted as heterogeneous nucleating agents. Transmission electron microscopy shows that the nano-sized bean-like Al_3Sc phase precipitated from the saturated solid solution. Moreover, the phase transition analysis of the 0.3-0.4SC alloy during solidification shows that the formation of the W phase underwent two different types of reactions: the peritectic-eutectic reaction (L + Al_3Sc → aAl + W) and eutectic reaction (L → aAl + W, L→ aAl + θ + W). The W phase formation mechanism of these two reactions is revealed through experiments. Simultaneously, W phases with different morphologies are observed in the 0.3-0.4Sc alloy, i.e., the W phase of the spherical-shell structure is formed by the peritectic-eutectic reaction, and the long strip W phase (~6 um in size) is precipitated by the eutectic reaction.
查看更多>>摘要：A hybrid-material of titanium-oxide quantum dots (QDs) anchored on graphene nanoribbons (TiO_2@GNRs) was prepared by a simple hydrolysis strategy followed by heat-treatment. The GNRs can effectively accelerate the charge transference in the TiO_2@GNRs. And the TiO_2 QDs of ~5 nm can be thoroughly lithiatied/ sodiated in electrically confined space of GNRs. Motivated by its unique structure, the electrochemical charge/discharge behaviors of the TiO_2@GNRs serving as anodes for Li/Na-ion batteries (LIBs/SIBs) were evaluated. Reversible charge capacities of 320.8 mAh g~(-1) for LIBs and 101.6 mAh;g~(-1) for SIDs were demonstrated over 100 cycles at a rate of 0.5 A g~(-1), respectively. And Li and Na storage capacities of 209.0 and 42.2 mAh g~(-1) were retained at 8.0 A g~(-1) respectively. The desirable charge capacities, stable cyclic ability, and excellent rate performance of TiO_2@GNRs can be ascribed to the ultra-small TiO_2 size benefiting for full insertion/extraction of alkali ions and shortening their transfer pathway as well as enhanced electronic and ionic conductivity of the overall electrodes and interfacial confinement of GNRs for maintaining the electrode integrity.
查看更多>>摘要：In this study, solvothermal method was adopted to successfully prepare graphene oxide (GO) supported SnO_2 nanocomposites using tin tetrachloride pentahydrate and graphene oxide as raw materials, tetra-methyl ammonium hydroxide (TMAH) as a control agent. The synthetic materials presented the efficient capacity in the photocatalytic degradation and photoelectric conversion. In the photocatalytic degradation of rhodamine B (RB) and methylene blue (MB), sample SnO_2-0.1% GO showed the optimal photocatalytic efficiencies for RB (97.26%) and MB (89.43%) degradation. According to the different degradation performances of RB and MB functional groups, we reasonably explained the electron transfer mechanism at the interface of SnO_2-GO nanomaterials, and verified it in the experiment of photoelectric conversion proceed combined with titanium dioxide nanotube arrays (TiO_2NTs). The enhanced photocurrent density and stability can also be effectively improved due to the effective photoelectron transfer from SnO_2 to GO surface.
查看更多>>摘要：Tin oxide (SnO_2) is widely used in metal-oxide-semiconductor for gas-sensing materials due to its unique physical and chemical properties. The grain size is one of the major influencing factors that determine the gas-sensing characteristics. In this work, a facile hydrolysis-oxidation-hydrothermal method is used to prepare the size-controllable SnO_2 quantum dots (QDs) of 4.7-8.9 nm, and the gas-sensing characteristics of the SnO_2 QDs sensors are evaluated by C_4H_(10), H_2 and C_2H_5OH at room temperature. The experimental results show that the resistance has a negative correlation with hydrothermal time, and the maximum response is obtained when the grain radius is comparable to the depletion layer width. A comprehensive model is proposed by considering all gas-sensing procedures of the receptor function, the transducer function and the utility factor. The sensor properties are formulated as functions of grain size, depletion layer width, film thickness, oxygen vacancy density, gas concentration, pore size as well as operating temperature. The present model provides a comprehensive mathematical interpretation of the size effects of SnO_2 from partial depletion to volume depletion.
查看更多>>摘要：Flexible supercapacitors (SCs) can usually be used as potential candidates for small flexible electronic devices, due to their good flexibility, rapid charge-discharge ability, and long-term cycling stability. Here, a facile solvothermal approach has been developed to prepare flexible and high-performance nitrogen-doped Ti_3C_2 MXene film electrodes for symmetric SCs. The effects of different solvents on the atomic structure, surface microstructure, and charge storage mechanism of N-doped Ti_3C_2 films were studied to explore the defect engineering of MXene for the enhancement of capacitive performance. Because of the comprehensive effects of the mixed solvents (diethanolamine (DEA) and isopropyl alcohol (IPA)) and the large inner pressure under the ex situ solvothermal process, the as-prepared N-doped Ti_3C_2 film fabricated from DEA and IPA with a volume ratio of 1:1 (IPAD-Ti_3C_2) shows a superhigh capacitance of 2846.5 F cm~(-3) at 5 mV s~(-1) and excellent stability. In addition, the IPAD-Ti_3C_2 film-assembled symmetric SC delivers a relatively large volumetric energy density of 64.0 Wh L~(-1) and a superhigh volumetric power density of 118,033.3 W L~(-1) at 1000 mV s~(-1). This work provides a feasible solution to improve the application potential of MXenes and, more broadly, binary metal carbides by ex situ nitrogen doping with mixed solvents.
查看更多>>摘要：In this work, to enhance the mineralization of the organic dyes, the g-C_3N_4(Ag)/Gr/TiO_2 Z-scheme photo-catalyst was successfully prepared by hydrothermal method. The XRD and XPS results showed that the nanocomposite was constructed. The SEM and EDS results showed that the morphology of g-C_3N_4(Ag)/Gr/ TiO_2 was that TiO_2 nanoparticles distributed on the surface of the Gr/g-C_3N_4 layers. The photocatalytic performance of the prepared samples was evaluated by the photocatalytic degradation and mineralization of RhB under visible light irradiation. The degradation efficiency of RhB on g-C_3N_4(Ag)/Gr/TiO_2 reached 99.7% within 2 h, and the kinetic rate (0.0431 min~(-1)) was 7.1, 7.1, 2.2, 2.0 and 1.3 times higher than those of g-C_3N_4, TiO_2, g-C_3N_4(Ag)/Gr, g-C_3N_4/TiO_2, and g-C_3N_4/Gr/TiO_2, respectively. The total organic carbon (TOC) removal results showed that the mineralization efficiency of RhB on this composite was as high as 74.5% after 2 h of reaction time. During the photocatalytic process, it was speculated that Gr acted as the electron transporter between TiO_2 and g-C_3N_4, which reduced the recombination efficiency of photo-generated charge carriers, and silver clusters acted as an electron reservoir to accelerate the reduction reaction of photo-generated electrons on the g-C_3N_4 conduction band, and further improved the photocatalytic performance.
查看更多>>摘要：Annealing at different temperatures was applied to a hot-rolled Ti-15Nb-5Zr-4Sn-1Fe (wt%) alloy to obtain α+β dual-phase structure with varying a phase fraction. The evolutions of a + p dual-phase structure, mechanical properties, and deformation mechanisms were systematically investigated. With increasing a phase from 5.5% to 33.7%, the stability of the retained p matrix was gradually enhanced and the p domain size was decreased. The deformation mechanisms changed from stress-induced p to a' martensitic transformation to stress-induced p to a" martensitic transformation, mechanical twinning of the p matrix, and finally dislocation slip accompanied with increasing a phase. Accordingly, Young's modulus decreased monotonously attributed to gradually suppressed athermal a phase, while the yield strength first decreased slightly owing to the change of stress-induced martensite from a' to a", and then increased rapidly when the long-range stress-induced martensite was suppressed. A good combination of low Young's modulus, high strength, and high ductility was obtained in a microstructure composed of ultrafine grained α+β dual-phase showing dislocation dominated plastic deformation. This study possibly serves as a templet to guide the development of ultrafine grained α+β dual-phase structured metastable p-Ti alloy for biomedical application.
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Elsevier