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71.
72.
《International Journal of Hydrogen Energy》2019,44(60):32184-32191
In order to reduce the cost of oxygen reduction reaction (ORR) catalyst in fuel cell, polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) three-block copolymer (F127) and Zn(OH)2 were used as carbon resource and morphology retaining agent to prepare porous nanocages for ORR catalyst in alkaline solution. Its composition and microstructure were characterized by X-ray diffraction Raman spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) method. Electrochemical properties were evaluated in O2 saturated alkaline solution. Results showed the sample obtained at 700 °C (C-700) was composed of porous carbon nanocages with diameter of 50 nm and shell thickness of 4 nm. C-700 had the maximum surface area (1011 m2 g−1) and the best ORR catalytic performance. The main reason is that polypropylene oxide (PPO) group at the lipophilic end begins to decompose at 500 °C, and the polyethylene oxide (PEO) group at the lipophilic end at 700 °C decomposes completely. In O2 saturated 0.1 M KOH solution, C-700's oneset potential, limit current density and half-wave potential, which were 0.89 V, 5.59 mA/cm2@0.45 V and 0.71 V, respectively, were close to that of commercial 20% Pt/C catalyst. It was noted that the oneset potential and half-wave potential of C-700 had barely change, and limit current density attenuated about 87.8% after 2000 CV cycle. The obtained catalyst behaved good catalytic activity and stability for ORR in alkaline solution and a potential application prospect in fuel cells. 相似文献
73.
《Acta Materialia》2003,51(17):5083-5092
Mo5Si3 exhibits a high anisotropy of its coefficients of thermal expansion (CTEs) in the a and c directions, i.e., CTE(c)/CTE(a)=2.0. The high CTE anisotropy is due to the existence of prominent atom chains along the c-axis. Ternary alloying additions that effectively stretch the atom chains are likely to reduce the bonding directionality/strength and CTE anisotropy. First-principles local-density-functional calculations were carried out for two alloy systems, MoNb4Si3 and Mo4VSi3. Indeed, we find a significant reduction of the CTE ratio to a value of 1.5 for MoNb4Si3 and a value close to 1.0 for Mo4VSi3. The decrease in the CTE anisotropy mainly comes from the reduction in CTE in the c-direction. While a conventional approach to reduce the CTE would involve an increase in lattice rigidity by increasing the bond strength, our strategy focuses on the reduction of driving force for thermal expansion by decreasing the bond directionality. 相似文献
74.
《Scripta materialia》2003,48(4):403-408
The thermoelectric oxide NaxCo2O4 was synthesized by the polymerized complex method, which provided a flaky powder. The sintered sample showed a high density, a fine microstructure and improved thermoelectric performance compared to a sample prepared by the conventional solid state reaction method. 相似文献
75.
《Food quality and preference》2002,13(2):89-97
A statistical method to reduce a large set of variables to a smaller subset of variables was published by Krzanowski [Krzanowski, W. J. (1987). Selection of variables to preserve multivariate data structure, using principal components. Applied Statistics, 36(1), 22–33]. An application in the field of sensory science is presented in this paper. The method selects the subset from all possible subsets by matching the multidimensional configuration of objects of the subset to the full set of variables. To this end a Procrustes rotation is used and the subset which produces the lowest Procrustes loss in this matching is selected as the optimal subset. For two data sets the loss values of all possible subsets of all possible sizes are studied. It is concluded that considering the subsets corresponding to a range of lowest loss values should be considered instead of only the subset producing the lowest loss value. The method can easily be extended to include fitting methods other than Procrustes rotations and other optimality criteria than the Procrustes loss employed here. 相似文献
76.
Prof. Dr. Hao Jiang Prof. Dr. Xiao-Yu Hu Dr. Stefanie Mosel Prof. Dr. Shirley K. Knauer Dr. Christoph Hirschhäuser Prof. Dr. Carsten Schmuck 《Chembiochem : a European journal of chemical biology》2019,20(11):1410-1416
Branched and dendrimeric cationic peptides have shown better transfection efficiency than linear peptides, owing to their superior capacity for inducing DNA condensation. We have designed and synthesized two analogously guanidinocarbonylpyrrole-substituted (GCP-substituted) branched cationic tripeptides that provide extremely strong electrostatic attraction towards DNA. Both ligands 1 and 2 can bind to DNA and form condensed complexes, owing to the branched structure and high positive charges, as demonstrated by isothermal titration calorimetry (ITC), ζ potential and atomic force microscopy (AFM). After the replacement of the carboxylate group by an amide group, binding of ligand 2 to DNA shows exothermic enthalpy and positive entropy changes relative to ligand 1 . Rational interpretation would suggest that ligand 2 might aid the translocation of plasmid pF143 to HEK 293T cells, showing high gene transfection efficiency. This work therefore provides a facile way, by modifying a branched cationic tripeptide with GCP, to turn a peptide even a tripeptide into an efficient gene transfection vector. 相似文献
77.
《Carbon》2015
Fabrication of graphitized carbon materials (e.g. carbon nanotubes and graphene) normally entails the assistance of transition metal catalyst. In this paper, a nitrogen doped carbon foam (NCF) with both graphitized and porous carbon structure was fabricated by direct pyrolysis of melamine foam (MF) without using any transition metal catalyst. The graphitized carbon structure was possibly attributed to the triazine moieties in the MF precursor. The introduction of oxygen groups in the oxidation step resulted in the formation of large amount of micro- and mesopores and therefore high specific surface area. The NCF exhibited a three-dimensional cellular network consisting of carbon microfiber with abundant micro- and mesopores and giving rise to a specific surface area over 980 m2 g−1. Due to such graphitized porous structure, the NCF was demonstrated to have superior resilience, excellent electrocatalytic activity and good durability for oxygen reduction. 相似文献
78.
《Ceramics International》2020,46(2):1343-1351
((Bi0.5Na0.5TiO3)0.88-(BaTiO3)0.12)(1-x)-(LiNbO3)x (x = 0.0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, and 0.07; abbreviated as LiNbO3-doped BNT-BT) ceramics possessing many excellent performances (large electrostrain, negative electrocaloric effect and energy storage density with high efficiency) was fabricated by the conventional solid-state reaction method. A large electrostrain (maximum ~ 0.34% at 100 kV/cm and room temperature) with high thermal stability over a broad temperature range (~80 K) is obtained at x = 0.03. A large energy storage density (maximum Wenergy ~ 0.665 J/cm3 at 100 kV/cm and room temperature) with a high efficiency (η ~ 49.3%) is achieved at x = 0.06. Moreover, a large negative electrocaloric (EC) effect (maximum ΔT ~ 1.71 K with ΔS ~ - 0.22 J/(K kg) at 70 kV/cm)) is also obtained at x = 0.04. Phase transition (from ferroelectric to antiferroelectric and then to relaxor) induced by increasing the doping amount of LiNbO3 plays a very key role on the optimization of these performances. These findings and breakthroughs make the LiNbO3-doped BNT-BT ceramics very promising candidates as multifunctional materials. 相似文献
79.
Effect of pyrolysis temperature on the mechanical evolution of SiCf/SiC composites fabricated by PIP
《Ceramics International》2020,46(2):1297-1306
Three types of SiCf/SiC composites with a four-step three-dimensional SiC fibre preform and pyrocarbon interface fabricated via precursor infiltration and pyrolysis at 1100 °C, 1300 °C, and 1500 °C were heat-treated at 1300 °C under argon atmosphere for 50 h. The effects of the pyrolysis temperature on the microstructural and mechanical properties of the SiCf/SiC composites were studied. With an increase in the pyrolysis temperature, the SiC crystallite size of the as-fabricated composites increased from 3.4 to 6.4 nm, and the flexural strength decreased from 742 ± 45 to 467 ± 38 MPa. After heat treatment, all the samples exhibited lower mechanical properties, accompanied by grain growth, mass loss, and the formation of open pores. The degree of mechanical degradation decreased with an increase in the pyrolysis temperature. The composites fabricated at 1500 °C exhibited the highest property retention rates with 90% flexural strength and 98% flexural modulus retained. The mechanism of the mechanical evolution after heat treatment was revealed, which suggested that the thermal stability of the mechanical properties is enhanced by the high crystallinity of the SiC matrix after pyrolysis at higher temperatures. 相似文献
80.
《Ceramics International》2020,46(8):12269-12274
Dielectric capacitors with high recoverable energy density are in high demand for their application in electrical and electronic systems. Among lead-free dielectric materials, silver niobate (AgNbO3) has attracted growing interest due to its superior energy storage density at room temperature. The field-induced phase transition from antiferroelectric (AFE) phase to ferroelectric (FE) phase contributes to its large energy density. In this work, pure perovskite silver niobate ceramics were fabricated in an oxygen atmosphere by the solid-state reaction technique. The Pbcm orthorhombic phase of AgNbO3 was closely observed using the Rietveld refinement method to provide explanation for the origin of high spontaneous polarization within a unit cell. Local structural analysis via piezoelectric force microscopy revealed the existence of ferroelectric nano domains, which may contribute to the high energy storage efficiency (η = 99.9926%) in AgNbO3 at low electric fields. The phase transitions of AgNbO3 were also investigated via the dependence of the dielectric permittivity (ε′ and ε″) and loss angle tangent (tanδ) on temperatures, providing insights into the further modification of AgNbO3. 相似文献