Electrocatalysis of oxygen evolution/reductionon LaNiO3 prepared by a novel malic acid-aided method

A kinetic study of the electroformation and electroreduction of oxygen in KOH solutions has been carried out on a LaNiO3 electrode obtained through a malic acid precursor route. The new electrocatalyst was found to show greatly enhanced activity for both oxygen evolution and reduction. The apparent electrocatalytic activity of this electrode for oxygen reduction was more than 10 times higher than those reported for similar electrodes obtained by other methods. It was, however, observed to be less active electrocatalytically for oxygen evolution as compared to the active LaNiO3 electrode obtained by the Bockris–Otagawa coprecipitation method. The electrochemical reaction order with respect to OH– concentration was found to be approximately 1 in the case of oxygen evolution while that for oxygen reduction, was approximately –1. The Tafel slope values for the reactions were 2.3RT/F and 2×2.3RT/3F, respectively.     

Imaging gold clusters on TiO2(110) at elevated pressures and temperatures

Variable temperature scanning tunneling microscopy (STM) has been used to image oxide-supported nanoclusters of Au at temperatures from 300 to 450 K and oxygen pressures from 10^–10 to 4 Torr. Oxygen-induced morphological changes of the TiO₂(1×2) reconstruction are apparent at room temperature and prolonged exposure (3×10³ L (langmuir)) at 10^–4 Torr oxygen. Gold clusters with diameters smaller than 4 nm are unstable toward sintering at ca. 450 K and oxygen pressures >10^–1 Torr. Oxygen at pressures >10^–4 Torr weakens the interaction between the gold cluster and the titania support. Increasing the sample temperature to >300 K facilitates disruption of the cluster–support interaction.     

Phase transition in swollen gels

Summary The photoelastic behaviour of two networks — polyacrylamide (PAAm) and of a network prepared by the copolymerization of acrylamide with 5 mol.% sodium methacrylate — was investigated in water-acetone mixtures. For the PAAm network the dependence of all photoelastic characteristics on the composition of the mixture is continuous. At 54 vol.% acetone in the mixture, the ionized network undergoes a transition which gives rise to jumpwise changes in the shear modulus, deformational-optical coefficient, C, and in the refractive index of the gel, n_g. While in the collapsed state the optical anisotropy of the statistical segment is negative, –3×10^–24 cm³ (indicating an interaction between the side chains), in the expanded state it is positive, 0.5 × 10^–24 cm³. The dependence of all optical characteristics on the composition of the mixtures suggests that: (a) in both networks we have a transition between two conformational states of the chain; while for the ionized network the transition is a discrete one, for the nonionized network it takes place in the range between 30 and 45 vol.% acetone in the mixture; (b) in both networks the gels are optically homogeneous throughout the whole range of compositions of the mixtures (and thus also in the close vicinity of the collapse of the ionized network).     

Synthesis and electrochemical characterization of a new Se-doped spinel material for lithium secondary batteries

A new Se-doped spinel material, LiAl_0.18Se_0.02Mn_1.8O₄ powder with a phase-pure polycrystalline was synthesized by a sol–gel method. The material in the 3 V region (2.4 3.5 V) and both the 3 and 4 V region (2.4 4.4 V) initially deliver a discharge capacity of 81 and 178 mA h g^–1 which increase with cycling to reach 110 and 204 after 50 cycles, respectively. The material shows excellent cycleability in the 4 V region (3.0 4.4 V) with almost no capacity loss. The structural integrity of the Se-doped spinel was characterized by charge–discharge cycling tests and X-;ray diffraction.     

Study of W/HZSM-5-Based Catalysts for Dehydro-aromatization of CH4 in Absence of O2. I. Performance of Catalysts

With incorporation of Zn (or Mn, La, Zr ) into the W/HZSM-5 catalyst, highly active and heat-resisting W/HZSM-5-based catalysts were developed and studied. Under reaction conditions of 0.1 MPa, 1073 K, GHSV of feed-gas CH₄+10% Ar at 960 h^–1, the conversion of methane reached 18–23% in the first 2 h of reaction, and the corresponding selectivity to benzene, naphthalene, ethylene and coke was 56–48, 18, 5 and 22%, respectively. Addition of a small amount of CO₂ (2%) to the feed-gas was found to significantly enhance the conversion of methane and the selectivity of benzene, and to improve the performance of coke-resistance of the W/HZSM-5-based catalysts. Heavy deposition of carbon on the surface of the functioning catalyst was the main reason leading to deactivation of the catalyst. Reoxidation by air may regenerate the deactivated catalyst effectively. In comparison with the Mo/HZSM-5 catalyst, the promoted W/HZSM-5-based catalyst can operate under reaction temperature of 1073 K, and gain a methane conversion approximately two times as high as that of the Mo/HZSM-5 catalyst operating at 973 K. It can also operate at 973 K and have about the same methane conversion as that of the Mo/HZSM-5 catalyst at the same reaction temperature. Its main advantage is its heat-resistant performance; the high reaction temperature did not lead to loss of W component by sublimation.     

Friction coefficient in gelatin and polyacrylamide gels

Summary The slow neutron transmission technique is used to measure the friction coefficient f of gel macromolecules moving against a solvent. It is shown that in the range of concentrations C=3–30%, f of gelatin gels is linearly dependent on C. The values of the monomer friction coefficient of gelatin and the friction coefficient at infinite dilution are determined. It is demonstrated that the friction coefficient of polyacrylamide gels varies as the viscosity of a solvent in a wide temperature range, however at temperatures below 25°C the deviation from proportionality is observed.     

A DRIFTS study of the morphology and surface adsorbate composition of an operating methanol synthesis catalyst

The nature of the species adsorbed on a Cu/ZnO/Al₂O₃ catalyst while it was producing methanol has been elucidated in this study using DRIFTS. The species are carbonates, formate, CO, oxygen atoms ( 2% of a monolayer) and methoxy on the Cu and methoxy on the ZnO. The frequencies observed for the C-O stretch on Cu, 2076, 2092, 2105 and 2132 cm^–1, have revealed the morphology of the copper component of the operating catalyst. The surface of the copper is predominantly the (111) face ( 65%) (the 2076 cm^–1 peak) with the (755) (the 2092 cm^–1 peak) and the (311) (the 2105 cm^–1 peak) faces occupying roughly 20% and 15%, respectively, of the copper area. The 2132 cm^–1 peak derives from CO adsorbed on Cu⁺ site on the copper which is 2% of a monolayer.     

An ac impedance study of the fractal geometry of silver films electrodeposited within a polymer matrix

Silver films (10^–6m) have been electrodeposited within a polymer matrix (10^–5 m) of polyvinylidene fluoride trifluoroethylene copolymer 60-40 cast on the surface of a stainless steel electrode. It is shown that the fractal geometry of the polymer-metal interface, which is not open to direct observation, can be characterized by means of ac impedance measurements made on the electrode in acetonitrile solution.     

Calculation of the Viscosity of Glass-Forming Melts: VI. The R2O–B2O3–SiO2and RO–B2O3–SiO2Ternary Borosilicate Systems

A method for calculating the viscosity from composition and temperature for melts in the R _m O _n –B₂O₃–SiO₂systems is proposed. The change in the concentrations of structural groups depending on the melt composition is taken into account in calculations. The results of calculations are compared with the experimental data available in the literature on the viscosity of 1200 melts with the use of the SciGlass information system. The root-mean-square deviation between the experimental and calculated characteristic temperatures varies from 30 K (for the glass transition temperature and the Littleton point) to 50 K (for a viscosity of 10⁴P).     

Scanning tunneling microscopy and spectroscopy of silver and platinum catalysts

Scanning tunneling microscopic studies of silver catalysts dispersed on highly oriented pyrolitic graphite (HOPG) with 2, 5 and 10 wt% metal loading prepared by wet impregnation and hydrogen reduction show spherical crystallites, with the 2 wt% catalysts having an average crystallite size of 2 nm and the 5 and 10 wt% catalysts with size distributions of 2–5 and 4–12 nm respectively. The Ag catalysts prepared by NaBH₄ reduction show a narrower size distribution. Pt/HOPG catalysts with 2 and 5 wt% metal loading prepared by wet-impregnation and hydrogen reduction show large (2–11 nm) raft-like crystallites; small crystallites ( 1 nm) could be obtained by NaBH₄ reduction. Tunneling spectroscopic measurements reveal the nonmetallic nature of crystallites on the surface of Ag(2 wt%)/HOPG as well as Pt/HOPG prepared by NaBH₄ reduction.     

Sex pheromone of Egyptian cotton leafworm (Spodoptera littoralis)

Samples of pheromone carriers, after use for 4–5 weeks in traps in the field, were analyzed. Partial isomerization of prodlure, (Z,E)-9,11-tetradecadienyl acetate (TDDA), the main component of the sex pheromone of femaleSpodoptera littoralis, took place. All three other possible isomers were formed to yield a mixture of 50% (Z,E)-9,11 -TDDA, 30% (E,E)-9,11-, 13% (E,Z)-9,11-, and 7% (Z,Z)-9,11 isomer. The process was found to be photochemically induced; none of these isomers was found under heating alone. Most of the pheromone, however, decomposed under field conditions.     

Comportement électrochimique d'alliages Cu-Ni-Cr microcristallins en milieu chlorure

Résumé La résistance à la corrosion des alliages Cu-Ni-Cr en milieu de NaCl dépend de leur taux de solidification, du rapport Ni/Cr et de la quantité de Cr. La solidification rapide (10⁵K s^–1) améliore considérablement la résistance à la corrosion de ces alliages. Cette amélioration est attribuable à leur homogénéité chimique et à la nature de la couche superficielle d'hydroxyde de chrome. La grande stabilité de cette couche passive, qui recouvre les rubans solidifiés rapidement, permet d'atteindre une diminution de 80% de la vitesse de corrosion comparativement à des lingots solidifiés lentement (100K s^–1).

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The corrosion resistance of Cu-Ni-Cr alloys in a NaCl environment depends on their solidification rate, the Ni/Cr ratio and the Cr content. Rapid solidification (10⁵K s^–1) considerably improves the corrosion resistance of Cu-Ni-Cr alloys. This improvement is attributed to the chemical homogeneity and the nature of the chrome hydroxide layer. The stability of this passive layer for rapidly solidified ribbons results in an 80% drop in the corrosion rate compared to ingots conventionally solidified (100K s^–1).

     

Electrical characteristics of 18650 Li-ion cells at low temperatures

Low temperature electrical performance characteristics of A&T, Moli, and Panasonic 18650 Li-ion cells are described. Ragone plots of energy and power data of the cells for different temperatures from 25 °C to –40 °C are compared. Although the electrical performance of these cells at and around room temperature is respectable, at temperatures below 0 °C the performance is poor. For example, the delivered power and energy densities of the Panasonic cells at 25 °C are 800 W l^–1 and 100 Wh l^–1, respectively, and those at –40 °C are <10 W l^–1 and 5 Wh l^–1. To identify the source for this poor performance at subambient temperatures, both two- and three-electrode impedance studies were made on these cells. The two-electrode impedance data suggests that the cell ohmic resistance remains nearly constant from 25 to –20 °C but increases modestly at –40 °C while the overall cell impedance increases by an order of magnitude over the same temperature range. The three-electrode impedance data of the A&T cells show that the increase in cell resistance comes mostly from the cathode electrolyte interface and very little either from the anode electrolyte interface or from the ohmic resistance of the cell. This suggests that the poor performance of the cells comes mainly from the high cathode–electrolyte interfacial impedance.     

Adsorption Isotherm and Pore Characteristics of Nano Alumina Derived from Sol-Gel Boehmite

This paper deals with a systematic investigation on the synthesis of aluminium oxide starting from mono hydroxy aluminium oxide (boehmite, (AlOOH)) which in turn is synthesized from aluminium nitrate. Boehmite on heating forms , transitional alumina and -alumina phases in the temperature range 400–600, 800–1050 and 1050–1100°C respectively. Calculation from XRD, using Scherer equation shows that -alumina has crystallite size in the range 5–10 nm, while and -alumina are in the range 10–20 nm and -alumina is about 33 nm. The textural features of aqueous sol-gel boehmite samples calcined at various temperatures were analyzed by specific surface area measurements and adsorption isotherm features. Maximum specific surface area of 266 m²/g is observed for the precursor calcined at 400°C and a minimum of 5 m²/g at 1100°C. Total pore volume is maximum for the precursor calcined at 600°C (0.2653 cm³/g). Average pore size ranges from 3 nm (400°C) to 11 nm (1100°C). The adsorption isotherms also show a change from Type IV to Type II with increase in temperature showing difference in surface properties. The information from t-plots, pore size distribution and cumulative pore volume data also indicates differences in porosity features of boehmite on calcination. The adsorption isotherm and pore size distribution analysis show maximum microporosity at 400°C, while maximum mesoporosity is observed at 600°C. At higher temperatures, porosity decreases, even though small fraction of pores in the mesopore range is still retained. At 1100°C, there is structural transformation from transitional to -alumina, with very low specific surface area 5 m²/g and pores in the size range of 11 nm. The various data presented in this study will be useful in the synthesis of alumina with tailor made properties.     

The kinetics of ethylene hydrogenation catalyzed by metallic palladium

The activity of Pd(111) for ethylene hydrogenation is measured using a high-pressure reactor incorporated into an ultrahigh vacuum chamber for temperatures between 300 and 475 K, ethylene pressures between 50 and 300 Torr and hydrogen pressures from 45 to 600 Torr. The reaction rate is found to be rapid with turnover frequencies up to 400 reactions/site/s (where rates are referenced to the atom site density on the (111) face of palladium). The measured activation energy is 35 kJ/mol. A hydrogen reaction order of 1.02 was found at a reaction temperature of 300 K and an ethylene pressure of 100 Torr, where the hydrogen reaction order was found to depend on temperature. A negative reaction order of –0.22 was found in ethylene pressure at a reaction temperature of 320 K and a hydrogen pressure of 100 Torr. The reaction rates are in good agreement with values obtained on silica-supported palladium and with other work on palladium single crystals.     

Partial oxidation of methane to syngas over Co/MgO catalysts. Is it low temperature?

Co/MgO catalysts with high Co-loading (>28 wt%) are able to initiate the reaction of methane with oxygen at temperatures around 500 °C. High conversions of methane ( 70%) and very high selectivities for hydrogen and carbon monoxide ( 90%) are obtained at very high reactant gas space velocities (10⁵–10⁶ h^–1). The temperature of the catalyst at the conditions of partial oxidation of methane to form syngas was found to be extremely high (1200–1300 °C); it is about 600–850 °C higher than that previously reported by others. At these temperatures, high temperature homogeneous reactions may prevail. It is suggested that combustion of methane to carbon dioxide occurs on the catalyst with major heat release and that methane and water, respectively methane and carbon dioxide are reformed thermally in an endothermic reaction leading to syngas.     

Performance and impedance studies of thin,porous molybdenum and tungsten electrodes for the alkali metal thermoelectric converter

Columnar, porous, magnetron-sputtered molybdenum and tungsten films show optinum performance as AMTEC electrodes at thicknesses less than 1.0 m when used with molybdenum or nickel current collector grids. Power densities of 0.40 W cm^–2 for 0.5 m molybdenum films at 1200 K and 0.35 W cm^–2 for 0.5 m tungsten films at 1180 K were obtained at electrode maturity after 40–90 h. Sheet resistances of magnetron sputter deposited films on sodium beta-alumina solid electrolyte (BASE) substrates were found to increase very steeply as thickness is decreased below about 0.3–0.4 m. The a.c. impedance data for these electrodes have been interpreted in terms of contributions from the bulk BASE and the porous electrode/BASE interface. Voltage profiles of operating electrodes show that the total electrode area, of electrodes with thickness <2.0 m, is not utilized efficiently unless a fairly fine (1×1mm) current collector grid is employed.     

Catalytic activity of Co,Mo and CoMo supported on NaY zeolite: hydrodesulfurization of gas oil at high pressure

Three series of Co/NaY, Mo/NaY and CoMo/NaY zeolite catalysts with variable metal content, prepared by a conventional impregnation method, were characterized by XRD, IR spectroscopy (oxide state) and acidity measurements (sulfide state), and tested in hydrodesulfurization (HDS) of gas oil at high pressure in the temperature range 275–350°C. The combined results of surface area, XRD and IR showed that in the catalysts with high metal loading a small loss in crystallinity and a partial blockage of the zeolite supercages were produced by Mo oxide species. The number of acid sites, which was lower for the Co/NaY than for the Mo/NaY catalysts, increased with increasing Co or Mo loading, but the strength of the acid sites was stronger for the Co/NaY series. HDS specific activities of the Co/NaY and Mo/NaY monometallic catalysts reached a maximum at very low loadings of Co ( 0.10 at. nm^–2) or Mo ( 0.16 at. nm^–2) by the double action of the metal sulfide species and the strong acid sites generated on the zeolite by the Co or Mo incorporation. In the binary CoMo/NaY catalysts, the synergy between Co and Mo species was significant for high Mo contents only.     

Detonation Properties and Electrical Conductivity of Explosive–Metal Additive Mixtures

Detonation properties of mixtures of condensed high explosives with metal additives are studied. A scheme of measurement of high electrical conductivity of detonation products ( > 10 ^–1 · cm^–1) with a time resolution of 10 nsec is developed. It is shown that the properties of detonation products depend significantly on the content of the additive in the HE and on dispersion and density of the mixture. The electrical conductivity of detonation products of the compositions examined reaches 5 · 10^{3 –1} · cm^–1, which is more than three orders higher than the electrical conductivity of the HE without the additive. Significant variation of electrical conductivity of detonation products over the conducting region thickness has been found. The main conductivity corresponds to a sector 1 mm long near the detonation front. The overdriven state of the detonation wave has a strong effect on electrical conductivity and conducting region thickness. It is assumed that the behavior of electrical conductivity with time is caused by successive processes of shock compression of the HE, excitation of the chemical reaction (including the reaction of the additive with detonation products), and expansion of detonation products. The measurement technique used is highly informative due to the possibility of studying detonation in various regimes.     

Livig carbocationic polymerization

Summary Diblock copolymers of isobytylene (IB) — methyl vinyl ether (MeVE) have been prepared by sequential monomer addition by employing 2-chloro-2, 4, 4-trimethylpentane (TMPCl)/TiCl₄ initiating system in the presence of nBu₄NCl or dimethyl-acetamide (DMA) in CH₂Cl₂/hexanes at –80°C. In line with our earlier observations (1), living carbocationic polymerizations (LCPZn) were obtained in the presence of nBu₄NCl (i.e., the molecular weight of the poly(vinyl methyl ether) segment increased upon TiCl₄ addition), however, extensive chain transfer occurred in the presence of DMA. According to column chromatography analysis, the product prepared in the presence of nBu₄NCl is essentially pure PIB-b-PMeVE diblock (96w%) contaminated with a very small amount (4w%) of PIB. In contrast, the product obtained with DMA contains only 21w% PIB-b-PMeVe together with 72w% PIB and 5w% PMeVe homopolymers. This large difference in blocking efficiencies suggests that the structures of the growing species are different in the presence of the common anion salt,nBu₄NCl, and the electron donor, DMA.For paper LIII in this series see Polym. Bull., vol. 29/1