查看更多>>摘要：A rational design and selection of electrocatalytic cathode host materials are significant to achieve sustainable, efficient and stable catalysis towards H2O2 electroreduction. Herein, we described a facile synergetic strategy to generate a novel free-standing electrode (Pd-Co3O4/3D RGO@polyimide (PI) foam, PCRP) with well-developed porous and hollow structure, which derived from cobalt-based MOFs (ZIF-67) as an advanced Pd host, rooting on the 3D conductive graphene/PI foam to realize the significant promotion towards H2O2 electroreduction. Such 3D hollow structure design not only offers a high specific area to develop a number of exposed catalytic activity sites but also restricts the aggregation of nanoparticle catalysts within catalysis. Utilizing the electrode structural advantages and reducing the particle diameter of noble metal catalysts to improve the catalytic performance was possible. When evaluated as a co-catalyst for H2O2 electroreduction, the as-developed electrode displayed an optimized reduction current density of 962 mA·cm?2 at ?0.8 V in alkaline due to the synergetic influence of Pd nanoparticles and Co3O4 hollow cages. Notably, the loading of noble metal on the PCRP electrode was only close to 2.0 wt% in Pd-Co3O4 hybrids. What's more, the obtained PCRP electrode also exhibited robust stability, low apparent activation energy (9.071 kJ·mol?1), good reproducibility and repeatability (903 mA·cm?2after 1000 cycles with a 0.0058% current density decay per cycle at ?0.8 V) superior to that of single Co3O4 nanoparticles or Co3O4/3D RGO hybrids with simple configuration, implying its great promise for novel energy transformation systems.
查看更多>>摘要：Owing to the alteration in the fundamental properties even by a slight variation in Cu/S ratio, the Cu–S system has been complicated and its role in photoconductive devices has been rarely investigated. Herein, CuS and Cu9S5 micro-flowers have been synthesized via a single-step solvothermal process and their photoconductors have been fabricated to unveil the optoelectronic characteristics. By increasing a Cu/S ratio from CuS to Cu9S5, the reduction in bandgap from 1.60 to 1.09 eV has been observed. In addition, the impact of bandgap on conductivity under dark and light has been investigated. Under Halogen light exposure, ~110 times increase in the photocurrent for Cu9S5 has been observed than CuS. The detectivity and responsivity of CuS and Cu9S5 were obtained to be 9.26 × 105, 6.1 × 106 Jones and 1.37 × 10?8, 1 × 10?6 A/W under Halogen light. In addition, the Cu9S5 photoconductor attained maximum responsivity, 2.5 × 10?4 A/W, and detectivity, 2.3 × 1010 Jones at 980 nm. More importantly, the photoconduction mechanism for CuS and Cu9S5 has been studied in-depth and the role of the Cu/S ratio on the photoconductivity has been evaluated.
查看更多>>摘要：Ti3C2Tx (MXene) materials with multilayered structures have been widely developed in various academic fields. However, the application of electromagnetic wave (EMW) absorption is limited because of the high conductivity, which leads to impedance mismatch. Herein, the impedance-matching properties were optimized by loading highly defective TiO2 onto an MXene sheet with S-doping and high-temperature annealing treatment. This treatment enhanced the EMW absorption because of the synergistic effect between the appropriate conductivity and enhanced polarization. The results show that S-doped MXene-300 has a conductivity of 2.70 × 10–5 S/cm and exhibits the best area of impedance matching among the investigated samples. When the as-prepared S-doped MXene-300 quality ratio with paraffin was 1:1, the minimum reflection loss could reach ?44.91 dB with a 4 mm coating thickness. In addition, the widest effective absorption (reflection loss ≤–10 dB) frequency bandwidth was 5.88 GHz when the thickness was 2.5 mm, which indicated that the dipolar polarization is the main positive EMW attenuation pathway for the S-doped MXene absorber. This research provides a new means of developing high-performance MXene EMW absorbers with adjustable conductivity and dielectric loss.
查看更多>>摘要：Titanium-iron (TiFe) is known to be highly sensitive to oxidation, and this impacts its use in hydrogen storage applications. To investigate the ability to control the surface oxidation of TiFe-based alloys, TiFe0.85Mn0.15 was used as a base alloy due to its ease of activation and the addition of Cr investigated to facilitate its re-activation upon oxidation. Upon the formation of TiFe0.85Mn0.15Crx (x = 0.15 and 0.30) an improvement in reactivation was observed. After exposure of TiFe0.85Mn0.15Cr0.30 to air for 2 h, the alloy could be re-activated at 150 °C under a 3 MPa hydrogen pressure. In comparison, a temperature of 300 °C under the same hydrogen pressure was needed to re-activate TiFe0.85Mn0.15. This indicates that Cr addition provided to some extent resistance against deactivation. This is also reflected in the HP-DSC measurements where a partial oxide reduction was observed at 100 °C for the oxidised TiFe0.85Mn0.15Cr0.30 alloy as opposed to the 220 °C of TiFe0.85Mn0.15. The partially reduced species acted as catalytic sites for hydrogen activation.
查看更多>>摘要：Flow behavior and dynamic recrystallization of a powder metallurgy EP962NP nickel-based superalloy in the (γ + γ′)-phase region have been investigated under the isothermal compression at 1075–1150 °C with strain rate of 0.0005–0.1 s?1. The results show that predicated solvus temperature of γ’ precipitates is as high as ~1196 °C. Flow stress behavior of experimental alloy exhibits typical characteristics of dynamic recrystallization (DRX) and can be well described by hyperbolic-sine Arrhenius-type model with a higher thermal deformation activation energy of 1181.7 kJ/mol. Discontinuous dynamic recrystallization can be identified as a dominant nucleation mechanism for DRX of the alloy, as evidenced by the prevalent observation of necklace structures. In addition, the refined recrystallized γ grains can be obtained with a higher strain rate due to the increasing deformation stored energy. During hot compression, the morphology of primary γ′ transforms from micron-scale irregular blocks to nano-scale spherical precipitates via the dissolution and re-precipitation process.
查看更多>>摘要：MXenes have a broad application in electrochemical energy storage. However, the smooth surface of high-density MXenes makes it difficult to stabilize the anchored active material. In this study, ultrathin Ti3C2 MXenes were doped with a high density of NiMoS4 nanoparticles with the assistance of dopamine (DA). DA was adsorbed by the Ti3C2 surface (Ti3C2-DA) to form a negatively charged layer, which was beneficial for the enrichment of metal ions. NiMoS4 was anchored to Ti3C2-DA via a hydrothermal reaction. The resultant Ti3C2-DA-NiMoS4 heterostructure increased the exposure of NiMoS4 active sites, and reduced the decrease in specific capacitance caused by volume changes. Consequently, Ti3C2-DA-NiMoS4 exhibited excellent electrochemical performance with a high specific capacitance of 1288 F g?1 at 1 A g?1. In addition, an asymmetric supercapacitor based on a Ti3C2-DA-NiMoS4 positive electrode achieved a high energy density of 40.5 Wh kg?1 at 810 W kg?1, and demonstrated excellent cycling stability (capacitance retention of 89% after 9000 cycles at 10 A g?1). These results demonstrate that the Ti3C2-DA-NiMoS4 heterostructure is a prospective candidate material for high-performance supercapacitors.
查看更多>>摘要：V2O5, as a positive electrode material in aqueous zinc ion batteries, is easy to collapse in the process of repeated charging and discharging of Zn2+, thus leading to an inferior electrochemical performance. In this paper, hydrated Na+ has been inserted into the V2O5 layer by a simple hydrothermal method to synthesize NaxV2O5·nH2O (NaVO). Electrochemical characterization of NaVO is as follows, which has a capacity of 452 mA h g?1 at 100 mA g?1 and a capacity holding of 79% after 1000 cycles at 4 A g?1, indicating that the insertion of hydrated Na+ can efficiently enhance high-rate performance of V2O5 cathode. In-situ XRD tests have been employed to reveal the underlying mechanism of the superior electrochemical performance. It is certified that hydrated Na+ incorporation not only provides support pillars for V2O5 thereby improving the stability of V2O5 structure, but also significantly reduces the material's desolvation penalty and enhances intercalation kinetics, which leads to a superior rate capability. These demonstrate the method that insertion of hydrated alkali metal ion into interlayer of nanomaterials is ideally suited for V-based material and other layered cathode materials for AZIBs.
查看更多>>摘要：The Al-3.3Cu-2.5Mn-0.5Zr (wt%) alloy was manufactured by electromagnetic casting and further subjected to processing including cold rolling, drawing and annealing. Excellent processability of the alloy at cold rolling and drawing was observed due to the ultrafine as-cast structure. Annealing of the cold-rolled strip at 350 °C for 48 h insignificantly reduces the hardness, but the electrical resistivity (ER) decreases by almost 3 times (from 115 to 40 nΩm). The large deformation during rolling (reduction 98.4%) and high fraction of the Zr- and Mn-bearing nano dispersoids (Al20Cu2Mn3 and Al3Zr-L12) stipulated the high set of mechanical properties and electrical conductivity after annealing at 400 °C (UTS~330 MPa, YS~250 MPa, EL~7%, 42.5 IACS). A model of ER dependence on the phase composition was proposed. While at above 400 °C there is a good agreement between the calculated and experimental values, the scatter at lower temperatures is attributed to exposure times insufficient for achieving the equilibrium (Al) composition. Atom probe tomography was employed for observation of Cu, Mn and Zr concentrations in (Al) after annealing at 350–450 °C. According to the experimental results and root-mean-square calculations, annealing at between 350 and 400 °C allows achieving (Al) compositions close to the equilibrium in reasonable time while with decreasing temperature the diffusion of Zr in (Al) decreases and thus it requires extremely long exposures, e.g. at 300 °C it is about 23,000 h. From this viewpoint annealing at below 350 °C is unreasonable for achieving lower ER.
查看更多>>摘要：Ultrafine Ni5P4 nanoparticles embedded in 3D porous carbon foams are designed and synthesized by the assistance of NaCl templating and followed a phosphorization treatment. The three-dimensional porous structure of the carbon foams possesses large active specific surface areas and sufficient pores, that help to buffer the volume expansions whilst offering conductive pathways to accelerate ion transportations. The ultrafine Ni5P4 nanoparticles are beneficial for the exposure more accessible active sites to enhance the capacity utilization and shorten ion transport distances. The Ni5P4/C composite presents high rate capability with a specific capacity of 192.5 mAh g-1 at 8000 mA g-1 and high cycle stability (363.7 mAh g-1 at 2000 mA g-1 after 3000 cycles) for lithium-ion batteries. Further, the composite is also examined as the anode for potassium ion batteries for the first time and it delivers a high specific capacity of 128.1 mAh g-1 after 5000 cycles at the current density of 2000 mA g-1. XRD measurements suggests a solid-solution reaction mechanism for K-ion storage in Ni5P4.
查看更多>>摘要：The polymer composites exhibiting reliable dielectric properties at high temperatures (>300 °C) are urgently required for cutting-edge electronic applications. In the present work, an interfacial reactive agent named 4-aminophxylphthalonitrile (4-APN), was covalently modified on the surface of the multiwalled carbon nanotubes (MWCNTs) to prepare the nitrile-functionalized multiwalled carbon nanotubes (MWCNTs-CN), which was further incorporated into the phthalonitrile end-capped polyarylene ether nitrile (PEN-ph) matrix to fabricate the high-temperature resistant PEN-ph/MWCNTs-CN composites. It was found that through facile heat-treatment, the crosslinked PEN-ph/MWCNTs-CN (7 wt%) composites exhibited a high glass transition temperature of 430 °C and stable dielectric properties (dielectric constant of 22.08 at 1 kHz) up to 350 °C. Meanwhile, the energy storage density of the composite membrane increased from 0.59 to 2.18 J/cm3 with the increase of filler content, showing an increase of 269.5%. The nitrile-functionalization of MWCNTs can not only improve the interfacial compatibility between MWCNTs-CN and PEN-ph matrix resin but also make MWCNTs-CN play a role as a crosslinker to further improve the mechanical, thermal, and dielectric properties of the composites. Therefore, the PEN-ph/MWCNTs-CN composites prepared by interfacial crosslinking reaction in this work will serve as the candidate materials for high-temperature-resistant energy storage applications.
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Elsevier