Pt/WC-CNTs催化剂的制备及其对氧还原的电催化性能

通过表面修饰和还原碳化技术制备了以WC为主相的碳化钨/碳纳米管材料（WC-CNTs）,并进一步采用微波多元醇法载铂制备复合催化剂Pt/WC-CNTs。该催化剂相比于Pt/CNTs催化剂,具有更低的过电位、更大的电流密度和交换电流密度,且具有更小的电荷转移电阻和更好的氧还原选择性,显示了优异的氧还原电催化性能。XRD结果表明催化剂由多晶面的WC、Pt晶粒和CNTs组成,TEM和HRTEM显示细小的Pt颗粒均匀地分布在WC-CNTs表面。Pt颗粒和WC颗粒紧密接触,这有利于它们之间的催化协同效应,从而大大增强了Pt的氧还原催化活性。旋转圆盘电极研究结果表明Pt/WC-CNTs催化剂对氧还原反应为直接四电子过程。碳化钨/碳纳米管载铂催化剂性能优异、成本较低,在燃料电池阴极催化剂的研究应用中具有良好的发展前景。     

Dynamic Behavior of Pd Species in an LaFe<Subscript>0.95</Subscript>Pd<Subscript>0.05</Subscript>O<Subscript>3</Subscript> Perovskite

Abstract  

LaFe_0.95Pd_0.05O₃ prepared by a sol–gel process was stable under reducing atmospheres up to 1,073 K. Under reducing atmospheres metallic palladium left the LaFeO₃ lattice and ionic palladium was reversibly incorporated into the perovskite framework in oxidizing environments. The catalytic activity of LaFe_0.95Pd_0.05O₃ was higher than that of LaFeO₃.     

Synthesis and Characterization of Ferromagnetic BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanocrystals Using Novel Ionic Precursor Complex [Fe(opd)<Subscript>3</Subscript>]<Subscript>2</Subscript>[Ba(CN)<Subscript>8</Subscript>]

The following investigation reports the synthesis of novel complex [Fe(opd)₃]₂[Ba(CN)₈] and preparation of BaFe₂O₄ nanoparticles through thermal decomposition without using any surfactant. The complex was characterized via Furrier transform infrared spectroscopy (FT-IR), ultra violet-visible spectroscopy (UV–vis), conductivity measurement and elemental analysis. The synthesized crystals of inorganic precursor complex was transferred to furnace, where they were calcined under normal atmosphere condition at 900 °C for 4 h. Formation of BaFe₂O₄ was supported by FT-IR and energy-dispersive X-ray analysis. Hexagonal structure of nano-oxide was confirmed on powder X-ray diffraction. Furthermore, uniform morphology of nanocrystals were reported by scanning electron microscopy. The saturation magnetization (22 emu/g), remanent magnetization (6 emu/g) and coercivity (400 Oe) reported on vibrating sample magnetometer curve illustrates the promising industrial and medicinal applications of prepared mixed oxide.     

Self-oscillating microgels with Fe(phen)<Subscript>3</Subscript> catalyst induced by the BZ reaction under acid-free conditions

A novel self-oscillating microgels were prepared by copolymerization N-isopropylacrylamide (NIPAAm), organic acid and iron(II) 5-acrylamide-1,10-phenanthroline-bi (1,10-phenanthroline) (Fe(phen)₃), the catalyst for the Belousov-Zhabotinsky (BZ) reaction. The microgels were characterized by FTIR spectroscopy and scanning electron microscope (SEM). In order to illustrate the self-oscillating mechanism, the static water contact angles of the oxidized and reduced states of self-oscillating microgels were measured. In addition, the self-oscillating behaviors of the microgels were investigated in BZ system under acid-free conditions. Both the redox potential and transmittance self-oscillating were observed at room temperature.     

Heat resistant properties of PP/Al(OH)<Subscript>3</Subscript>/Mg(OH)<Subscript>2</Subscript> flame retardant composites

Vicat softening point temperature (T _V) and heat deflection temperature (T _d) are important parameters for characterization of heat resistant properties of polymeric materials. PP/Al(OH)₃/Mg(OH)₂ flame retardant composites were prepared using a twin-screw extruder, and the T _V and T _d of the composites were measured. The results showed that the T _V and T _d increased nonlinearly with an addition of the weight percentage of the flame retardant additives except for individual data points, while the T _V and T _d decreased with increasing the filler particle size when the content of flame retardant additives was constant. Under the same conditions, filling small amount of zinc borate into the composites might improve the heat resistant properties of the composite systems. Moreover, the morphology of the impact fracture surface of the specimens was observed by means of scanning electron microscope to understand the dispersion and distribution of the filler particles in the PP matrix.     

First-principles study of half-metallicity in semi-hydrogenated BC<Subscript>3</Subscript>, BC<Subscript>5</Subscript>, BC<Subscript>7</Subscript>, and B-doped graphone sheets

Using first principles calculations, we investigate the electronic structures of semi-hydrogenated BC₃, BC₅, BC₇, and B-doped graphone sheets. We find that all the semi-hydrogenated boron-carbon sheets exhibit half-metallic behaviors. The magnetism originates from the non-bonding p _z orbitals of carbon atoms, which cause the flat bands to satisfy the Stoner criterion. On the other hand, boron atoms weaken the magnetic moments of nearby carbon atoms and act as holes doped in the sheets. It induces the down shift of the Fermi level and the half-metallicity in semi-hydrogenated sheets. Our studies demonstrate that the semi-hydrogenation is an effective route to achieve half-metallicity in the boron-carbon systems.     

Hydrothermal synthesis of nanotubes based on (Mg,Fe,Co,Ni)<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> hydrosilicates

Hydrosilicate nanotubes of the variable composition (Mg,Fe,Co,Ni)₃Si₂O₅(OH)₄ with a chrysotile structure have been synthesized under hydrothermal conditions at temperatures of 250–450°C and pressures of 30–100 MPa in media of different compositions. The conditions and ranges of formation of nanotubular hydrosilicates of the compositions under investigation have been determined. It has been demonstrated that the type of cation of the octahedral layer in the chrysotile structure has a decisive effect on the physicochemical conditions, mechanism, and rate of formation of nanotubes, as well as on their structure, morphology, and sizes.     

Electrochemical behavior of K<Subscript>4</Subscript>Fe(CN)<Subscript>6</Subscript> in [bmim]PF<Subscript>6</Subscript>/TX-100/H<Subscript>2</Subscript>O based microemulsions

The electrochemical behavior of potassium ferrocyanide [K₄Fe(CN)₆] at Pt/ionic liquid (IL) microemulsion interfaces was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). H₂O/TX-100/bmimPF₆ was used to prepare three IL microemulsions: water in 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆) (W/IL), bicontinuous (WIL) and bmimPF₆ in water (IL/W). The results show that the IL microemulsion systems have relatively narrower potential windows compared with the pure IL system. The redox potential gap is about 100 mV in the pure water and the three IL microemulsions. The redox potentials of K₄Fe(CN)₆/K₃Fe(CN)₆ and the redox peak currents decrease in the order pure water, IL/W, WIL, W/IL. Furthermore, the peak currents increase linearly with the square root of the scan rate, while the diffusion coefficient increased in the order W/IL, WIL, IL/W. The Nyquist plots obtained in the WIL and IL/W systems show capacitive resistance arcs at high frequencies and 45° straight lines at low frequencies, implying that the electrochemical reactions are controlled by charge transfer and diffusion steps. For the W/IL system there is only a 45° straight line in the Nyquist plot, indicating that diffusion is the controlling step at all frequencies.     

On the Photomagnetic Properties of the Binuclear Spin Crossover Complexes {[Fe(bt)(NCSe)<Subscript>2</Subscript>]<Subscript>2</Subscript>(bpym)} and {[Fe(bpym)(NCSe)<Subscript>2</Subscript>]<Subscript>2</Subscript>(bpym)}

Infrared and visible light irradiation effects on the spin state of iron(II) ions have been investigated in the binuclear molecules {[Fe(bt)(NCSe)₂]₂(bpym)} (4) and {[Fe(bpym)(NCSe)₂]₂(bpym)} (2). For compound 2 we could observe LIESST and partial reverse-LIESST effects under visible and infrared light irradiation, respectively. Compound 4 exhibits a wavelength-selective photoconversion at 10 K from the low spin (LS–LS) ground state of the binuclear molecule to the metastable high spin (HS–HS) state under visible (785 or 532 nm) light irradiation or to the metastable HS–LS state under infrared (1,342 nm) light irradiation. In addition we also observed the reverse (HS–HS → HS–LS) and the cascade (LS–LS → HS–LS → HS–HS) photoconversions as well. These phenomena lead to complex and original photomagnetic behaviour due to the intramolecular magnetic coupling. This article is dedicated to Professor Didier Astruc in honor of his scientific achievements, with friendship and sincere respect.     

Isothermal vapor-liquid equilibria for the binary system of dimethyl ether (CH<Subscript>3</Subscript>OCH<Subscript>3</Subscript>)+ methanol (CH<Subscript>3</Subscript>OH)

Isothermal vapor-liquid equilibrium data for the binary mixture of dimethyl ether (CH₃OCH₃)+methanol (CH₃OH) were measured within the temperature range of 308.15–328.15 K. The data in the two-phase region were measured by using a circulation-type equilibrium apparatus in which both vapor and liquid phases are continuously recirculated. The experimental data were correlated with the Peng-Robinson equation of state (PR-EoS) using the Wong-Sandler mixing rules combined with the NRTL excess Gibbs free energy model. The values calculated by the PR-EOS with the W-S mixing rules show good agreement with our experimental data.     

On the structure of a Pd<Subscript>561</Subscript> giant palladium cluster

The structures of giant icosahedral close-packed clusters are considered in the framework of the local approach. A specific four-dimensional construction that consists of tetrahedra and octahedra and has symmetry of the {3, 3, 5} polytope is determined. It is demonstrated that the Pd₅₆₁ cluster is an icosahedral twin of fragments of both the face-centered cubic lattice and the hexagonal close packing simultaneously.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Shevchenko, Samoilovich, Talis, Madison.     

Solution-Combustion Synthesis of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> as a Cathode Material for Lithium-Ion Batteries

A cathode material for lithium-ion batteries–LiNi_1/3Co_1/3Mn_1/3O₂–was prepared by solution combustion synthesis and characterized by XRD, SEM, and galvanostatic charge/discharge cycling. The sample calcined at 950°C for 10 h showed best charge/discharge performance. An initial discharge capacity (C) of 150.5 mA h g^–1 retained 95.7% of its value after 75 charge/discharge cycles at I_c = 14 mA g^–1 (0.2C rate), I_d = 70 mA g^–1 (0.5C rate).     

A Highly Selective Pd(OAc)<Subscript>2</Subscript>/Pyridine/K<Subscript>2</Subscript>CO<Subscript>3</Subscript> System for Oxidation of Terpenic Alcohols by Dioxygen

Abstract  

Molecular sieves, complex organic bases and radical oxidants are commonly used in alcohols oxidation reactions. In this work, we have evaluated the beneficial effects of addition of K₂CO₃ to Pd(II)-catalyzed oxidation alcohols, which resulted in a remarkable increase in the oxidation reaction rates without selectivity losses. Herein, in a metallic reoxidant-free system, terpenic alcohols (β-citronellol, nerol and geraniol) were selectively converted into respective aldehydes from Pd(II)-catalyzed oxidation reactions in presence of dioxygen. High conversions and selectivities (greater than 90%) were achieved in the presence of the Pd(OAc)₂/K₂CO₃ catalyst and pyridine excess. The exogenous role of others auxiliary anionic and nitrogen compounds was appraised.     

Direct electrochemical reduction of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript> in CaCl<Subscript>2</Subscript> melt

The electrochemical reduction of Dy₂O₃ in CaCl₂ melt was studied. The cyclic voltammetry, chronoamperometry, AC impedance and constant voltage electrolysis were employed. A single cathodic current peak in the cyclic voltammogram and one response semicircle in the AC impedance spectrum were observed, supporting a one-step electrochemical reduction mechanism of Dy₂O₃. No intermediates were observed by XRD, which confirmed the following electrochemical reduction sequence: Dy₂O₃ → Dy. The charge transfer resistances and the activation energies involved in the electrochemical reduction step of Dy₂O₃ were obtained by simulating the AC impedance spectra with equivalent circuits. The electrochemical reduction reaction of Dy₂O₃ is controlled by the charge transfer process at a low voltage range and by the diffusion process at a high voltage range.