共查询到20条相似文献,搜索用时 703 毫秒
1.
M. Brandalise R. W. R. Verjulio-Silva M. M. Tusi O. V. Correa L. A. Farias M. Linardi E. V. Spinacé A. Oliveira Neto 《Ionics》2009,15(6):743-747
Pt/C, PtRu/C, PtBi/C, and PtRuBi/C electrocatalysts (20 wt.% metal loading) were prepared by borohydride reduction using H2PtCl6·6H2O, RuCl3·xH2O, and Bi(NO3)3·5H2O as metal sources and Vulcan XC 72 as support. The electrocatalysts were characterized by energy-dispersive X-ray analysis,
X-ray diffraction, and thermogravimetric analysis. The electro-oxidation of ethanol was studied in sulfuric acid solution
by cyclic voltammetry and chronoamperometry. The electrochemical studies showed that PtRuBi/C (50:40:10) electrocatalyst has
superior performance for ethanol electro-oxidation at room temperature compared to the other electrocatalysts. Preliminary
tests at 100 °C on a single direct ethanol fuel cell also confirm the results obtained by electrochemical techniques. 相似文献
2.
PtSn/C and PtSnSb/C electrocatalysts (20 wt.% metal loading) were prepared by an alcohol reduction process using H2PtCl6.6H2O, SnCl2.2H2O, and Sb(OOCCH3) as metal sources, ethylene glycol as solvent and reducing agent, and Vulcan XC72 as carbon support. The
electrocatalysts were characterized by energy dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy,
while that the performance for ethanol oxidation was investigated by cyclic voltammetry and chronoamperommetry (chrono) at
room temperature. The diffractograms of the PtSn/C and PtSnSb/C electrocatalysts showed four peaks associated to Pt face-centered
cubic structure and two peaks that were related to a SnO2 phase. For PtSb/C and PtSnSb/C electrocatalysts, no Sb (antimony) peaks corresponding to a metallic antimony or antimony
oxide phases were observed. Transmission electron microscopy images showed that the metal particles were homogeneously distributed
over the support. The PtSnSb/C (50:45:05) electrocatalyst showed an increase of performance for ethanol oxidation in relation
to PtSn/C electrocatalyst at room temperature. In the tests at 100 °C on a single cell of a direct ethanol fuel cell, the
maximum power density of PtSnSb/C (50:45:05) electrocatalyst was slightly higher than that of PtSn/C electrocatalyst. 相似文献
3.
E. V. Spinacé Ricardo R. Dias Michele Brandalise Marcelo Linardi Almir Oliveira Neto 《Ionics》2010,16(1):91-95
PtRh/C (90:10), PtRh/C (50:50), PtSn/C (50:50), and PtSnRh/C (50:40:10) electrocatalysts were prepared by an alcohol-reduction
process using ethylene glycol as solvent and reduction agent and Vulcan Carbon XC72 as supports. The electrocatalysts were
characterized by energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The electro-oxidation
of ethanol was studied by cyclic voltammetry chronoamperometry at room temperature and on a single cell of a direct ethanol
fuel cell at 100 °C. Cyclic voltammetry and chronoamperometry experiments showed that PtSnRh/C and PtSn/C electrocatalysts
have similar performance for ethanol oxidation at room temperature, while the activity of PtRh/C electrocatalysts was very
low. At 100 °C on a single cell, PtSnRh/C showed superior performance compared to PtSn/C and PtRh/C electrocatalysts. 相似文献
4.
J. C. Castro R. M. Antoniassi R. R. Dias M. Linardi E. V. Spinacé A. Oliveira Neto 《Ionics》2012,18(8):781-786
PtSnRh/C-Sb2O5·SnO2 electrocatalysts with different Pt/Sn/Rh atomic ratios (90:05:05, 70:25:05, and 50:45:05) were prepared by an alcohol reduction process using H2PtCl6·6H2O, SnCl2·2H2O, RhCl3·xH2O as metal sources, ethylene glycol as solvent and reducing agent, and a physical mixture of Vulcan XC72 (85?wt%) and Sb2O5·SnO2 (15?wt%) as support. The electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. The electro-oxidation of ethanol was studied by cyclic voltammetry and chronoamperometry at 25 and 50?°C and in single direct ethanol fuel cell (DEFC) at 100?°C. The diffractograms of PtSnRh/C-Sb2O5·SnO2 electrocatalysts showed the peaks characteristic of Pt face-centered cubic structure and several others peaks associated with ·SnO2 and Sb2O5·SnO2. Transmission electron micrographs of PtSnRh/C-Sb2O5·SnO2 electrocatalysts showed the metal nanoparticles distributed on the supports with particle sizes of about 2?C3?nm. The electrochemical measurements and the experiments in a single DEFC showed that PtSnRh/C-Sb2O5·SnO2 (90:05:05) and PtSnRh/C-Sb2O5·SnO2 (70:25:05) electrocatalysts exhibited higher performance for ethanol oxidation in comparison with PtSnRh/C electrocatalyst. 相似文献
5.
Ce0.9Gd0.1O1.95 (GCO), is one of the potential candidate electrolytes for intermediate temperature Solid Oxide Fuel Cells (ITSOFC). GCO has
high oxide ion conductivity in the intermediate temperature range (500 – 700 °C) compared to other Ce1−yGdyO2-2/y compositions and the Gd3+ ion is the most appropriate dopant material compared to other rare earth materials such as Sm3+, Y3+, Zr3+, etc. Our results show that the fuel cell H2/Pt/Ce0.9Gd0.1O1.95/Pt/O2 operated in the temperature range 500 – 700°C gives the maximum power densities 0.0049 W/cm2 at 500 °C and 0.0126 W/cm2 at 650 °C for cell voltages 0.6275 V and 0.6278 V, respectively, where the electrolyte was kept in 5% H2 (+ Argon) for 12 hours before use in the fuel cell. Maximum power densities are 0.0038 W/cm2 at 500 °C and 0.0270 W/cm2 at 650 °C for cell voltages 0.5986 and 0.5913 V, respectively, where the electrolyte was kept in 2 % O2 (+ Argon) for 12 hours before use in the fuel cell.
Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003. 相似文献
6.
《Proceedings of the Combustion Institute》2023,39(1):511-519
The auto-ignition properties of ammonia (NH3)/ethanol (C2H5OH) blends close to engine operating conditions were investigated for the first time. Specifically, the ignition delay times (IDT) of ammonia/ethanol blends were measured in a rapid compression machine (RCM) at elevated pressures of 20 and 40 bar, five C2H5OH mole fractions from 0% to 100%, three equivalence ratios (ϕ) of 0.5, 1.0 and 2.0, and intermediate temperatures between 820 and 1120 K. The measurements reveal that ethanol can drastically promote the reactivity of ammonia, e.g., the auto-ignition temperature with merely 1% C2H5OH in fuel decreases accordingly around 110 K at 40 bar as compared to that of neat ammonia. Moreover, the promotion efficiency of ethanol is higher than hydrogen and methane with a factor of 5 and 10 under the same condition. Different dependences of IDT on the equivalence ratio were observed with different ethanol fractions in the blends, i.e., the IDTs of the 5%, 10% and 100% C2H5OH in fuel decrease with an increase of ϕ, but an opposite trend was observed in the mixture with 1% C2H5OH. A new chemical kinetic mechanism for NH3/C2H5OH mixtures was developed and it is highlighted that the addition of cross-reactions between the two fuels is necessary to obtain reasonable simulations. Basically, the newly developed mechanism can reproduce the measurements of IDT very well, whereas it overestimates the reactivity of the stoichiometric and fuel-rich mixture with 1% C2H5OH in fuel. The sensitivity, reaction pathway, as well as rate of production analysis indicated that the ethanol addition to ammonia fuel blends provides key interaction pathways and enriches the O/H radical pool which further promotes the auto-ignition process. 相似文献
7.
PtSn/C electrocatalysts (Pt:Sn atomic ratios of 50:50 and 60:40) were prepared using citric acid as reducing agent, and the
pH of the reaction medium was varied by the addition of OH− ions. The obtained electrocatalysts were characterized by energy dispersive X-ray analysis, X-ray diffraction, and transmission
electron microscopy. The electrocatalysts were tested on the direct ethanol fuel cell (DEFC) at 90 °C. The obtained PtSn/C
electrocatalysts showed the presence of a face-centered cubic, Pt, and SnO2 phases. In DEFC studies, the PtSn/C electrocatalysts showed a superior performance compared to a commercial PtSn/C and Pt/C
electrocatalysts from E-TEK. 相似文献
8.
《Proceedings of the Combustion Institute》2023,39(1):395-403
To extend the temperature for propane ignition to a lower region (< 680 K), ozone (O3) was used as an ignition promoter to investigate the low-temperature chemistry of propane. Ignition delay times for propane containing varying concentrations of O3 (0, 100, and 1000 ppm) were measured at 25 bar, 654–882 K, and equivalence ratios of 0.5 and 1.0 in a rapid compression machine (RCM). Species profiles during propane ignition with varying O3 concentrations were recorded using a fast sampling system combined with a gas chromatograph (GC). A kinetic model for propane ignition with O3 was developed. O3 shortened ignition delay times of propane significantly, and the NTC behavior was weakened. O atoms released from O3 reacted with propane through hydrogen abstraction reactions, which led to the fast production of OH radicals. The following oxidation of fuel radicals generated additional OH radicals. Consequently, the inhibition caused by the slow chemistry of hydrogen peroxide (H2O2) in the NTC region was weakened in the presence of O3. Experimental results with O3 addition can provide extra constraints on the low-temperature chemistry of propane. Species profiles during propane ignition at 730 K with 1000 ppm O3 addition showed the production of propanal (C2H5CHO), acetone (CH3COCH3), and acetaldehyde (CH3CHO) was promoted significantly. Model analyses indicated that O3 shifted the oxidation temperature of propane to a lower region, in which reactions of ROO radicals (NC3H7O2 and IC3H7O2) tend to generate RO radicals (NC3H7O and IC3H7O). The promotion of RO radicals led to the fast production of C2H5CHO, CH3COCH3, and CH3CHO. The corresponding species profile highlighted the reaction relevant to ROO and RO radicals (NC3H7O + O2 = C2H5CHO + HO2 and 2 IC3H7O2 = 2 IC3H7O + O2). Rate constants of these reactions were updated, which can potentially improve the performance of the core mechanism under lower temperatures and provide references for model development of larger hydrocarbons. 相似文献
9.
Single crystals of YAl3(BO3)4 doped with 5% Sm3+ were grown by spontaneous nucleation from K2Mo3O10 and B2O3 flux. Photoluminescence spectra at room and low temperatures were measured. Four emission transitions have been observed from the 4G5/2 excited state to the lower lying states 6H5/2, 6H7/2, 6H9/2 and 6H11/2 upon exciting the sample with 400 nm wavelength. Polarized absorption spectra in UV, visible and NIR regions were recorded for two light polarizations (π and σ) relative to the C3 crystal axis.Energy levels scheme of the doping ion has been compiled after a careful analysis of the spectra by reproducing the observed transitions by means of theoretical calculations based on a Hamiltonian including the free-ion and the crystal-field (CF) terms. Free-ion and crystal-field analyses are performed based on a D3 point-group symmetry Hamiltonian. A best fit between theoretical and experimental energy levels is obtained with a root-mean-square (rms) deviation of 16 cm?1. The general trend of the crystal-field parameters of rare earth ions in YAB host is confirmed. The calculated NV crystal-field strength parameter presents a linear variation with the rare earth ionic radii and with the 4fn electron number. 相似文献
10.
Degradation of C.I. Direct Black 168 from aqueous solution using Fenton-like reactions combining ultrasound was investigated. In the presence of H2O2, the effect of the heterogeneous catalysts, such as fly ash, kaolinite or diatomaceous earth on the degradation of Direct Black 168 was observed under ultrasound. The fly ash was the most efficient catalyst. It is apparent that ultrasound can prompt the reaction to take place and give in higher degradation. In the combination of ultrasound and fly ash/H2O2, the effect of different system variables namely concentration of the dye, dosage of fly ash, concentration of H2O2, pH of solution and the addition of NaCl were studied. 99.0% removal ratio was achieved at initial concentration 100 mg/L, pH 3.0, and dosage of fly ash 2.0 g/L, as well as 2.94 mM H2O2. NaCl exhibited only a minor effect on the dye removal. 相似文献
11.
BaCe0.7Ta0.1Y0.2O3−
δ
(BCTY) and BaCe0.8Y0.2O3−
δ
(BCY) were synthesized by solid-state reaction method at 1,300 °C for 20 h. After being exposed in 3% CO2 + 3% H2O + 94% N2 at 700 °C for 20 h, the BCTY exhibited adequate chemical stability against carbonations while BCY decomposed into BaCO3 and CeO2. The BCTY showed the similar thermal expansion behavior to BCY from room temperature to 1,000 °C in air. The BCTY displayed
a conductivity of 0.007 S/cm at 700 °C in humid hydrogen, lower than that of BCY (0.009 S/cm). A fuel cell with 10-μm thick
BCTY membrane prepared through an all-solid-state process exhibited 1.004 V for OCV, 330 mW/cm2 for maximum output at 700 °C, respectively. Short-term test shows that the fuel cell performance does not degrade after 20 h. 相似文献
12.
《Proceedings of the Combustion Institute》2023,39(1):445-453
Methanol (CH3OH) has attracted considerable attention as a renewable fuel or fuel additive with low greenhouse gas emissions. Methanol oxidation was studied using a recently developed supercritical pressure jet-stirred reactor (SP-JSR) at pressures of 10 and 100 atm, at temperatures from 550 to 950 K, and at equivalence ratios of 0.1, 1.0, and 9.0 in experiments and simulations. The experimental results show that the onset temperature of CH3OH oxidation at 100 atm is around 700 K, which is more than 100 K lower than the onset at 10 atm and this trend cannot be predicted by the existing kinetics models. Furthermore, a negative temperature coefficient (NTC) behavior was clearly observed at 100 atm at fuel rich conditions for methanol for the first time. To understand the observed temperature shift in the reactivity and the NTC effect, we updated some key elementary reaction rates of relevance to high pressure CH3OH oxidation from the literature and added some new low-temperature reaction pathways such as CH2O + HO2 = HOCH2O2 (RO2), RO2 + RO2 = HOCH2O (RO) + HOCH2O (RO) + O2, and CH3OH + RO2 = CH2OH + HOCH2O2H (ROOH). Although the model with these updates improves the prediction somewhat for the experimental data at 100 atm and reproduces well high-temperature ignition delay times and laminar flame speed data in the literature, discrepancies still exist for some aspects of the 100 atm low-temperature oxidation data. In addition, it was found that the pressure-dependent HO2 chemistry shifts to lower temperature as the pressure increases such that the NTC effect at fuel-lean conditions is suppressed. Therefore, as shown in the experiments, the NTC phenomenon was only observed at the fuel-rich condition where fuel radicals are abundant and the HO2 chemistry at high pressure is weakened by the lack of oxygen resulting in comparatively little HO2 formation. 相似文献
13.
Composites of Al(H2PO4)3 and H3PO4 were synthesised by soft chemical methods with different Al/P ratios. The Al(H2PO4)3 obtained was found to have a hexagonal symmetry with parameter a = 13.687(3)Å, c = 9.1328(1)Å. The conductivity of this material was measured by a.c. impedance spectroscopy between 100 °C and 200 °C in different atmospheres. The conductivity of pure Al(H2PO4)3 in air is in the order of 10? 6–10? 7 S/cm between 100 and 200 °C. For samples containing small excess of H3PO4, much higher conductivity was observed. The impedance responses of the composites were found to be similar with AlH2P3O10·nH2O under different relative humidity. The conductivity of Al(H2PO4)3–H3PO4 composite with Al/P = 1/3.5 reached 6.6 mS/cm at 200 °C in wet 5% H2. The extra acid is found to play a key role in enhancing the conductivity of Al(H2PO4)3–H3PO4 composite at the surface region of the Al(H2PO4)3 in a core shell type behaviour. 0.7% excess of H3PO4 can increase the conductivity by three orders of magnitude. These composites might be alternative electrolytes for intermediate temperature fuel cells and other electrochemical devices. Conductivity (9.5 mS/cm) changed little, when the sample was held at 175 °C for over 100 h as the conductivity stabilised. 相似文献
14.
Huijun Guo Wenting Sun Francis M. Haas Tanvir Farouk Frederick L. Dryer Yiguang Ju 《Proceedings of the Combustion Institute》2013,34(1):573-581
H2O2 is one of the most important species in dimethyl ether (DME) oxidation, acting not only as a marker for low temperature kinetic activity but also responsible for the “hot ignition” transition. This study reports, for the first time, direct measurements of H2O2 and CH3OCHO, among other intermediate species concentrations in helium-diluted DME oxidation in an atmospheric pressure flow reactor from 490 to 750 K, using molecular beam electron-ionization mass spectrometry (MBMS). H2O2 measurements were directly calibrated, while a number of other species were quantified by both MBMS and micro gas chromatography to achieve cross-validation of the measurements. Experimental results were compared to two different DME kinetic models with an updated rate coefficient for the H + DME reaction, under both zero-dimensional and two-dimensional physical model assumptions. The results confirm that low and intermediate temperature DME oxidation produces significant amounts of H2O2. Peroxide, as well as O2, DME, CO, and CH3OCHO profiles are reasonably well predicted, though profile predictions for H2/CO2 and CH2O are poor above and below ~625 K, respectively. The effect of the collisional efficiencies for the H + O2 + M = HO2 + M reaction on DME oxidation was investigated by replacing 20% He with 20% CO2. Observed changes in measured H2O2 concentrations agree well with model predictions. The new experimental characterizations of important intermediate species including H2O2, CH2O and CH3OCHO, and a path flux analysis of the oxidation pathways of DME support that kinetic parameters for decomposition reactions of HOCH2OCO and HCOOH directly to CO2 may be responsible for model under-prediction of CO2. The H abstraction reactions for DME and/or CH2O and the unimolecular decomposition of HOCH2O merit further scrutiny towards improving the prediction of H2 formation. 相似文献
15.
The thermoluminescence (TL) properties of dode-calcium hepta-aluminate (Ca12Al14O33) enabled by 12CaO-7Al2O3 doped with rare earth and transitions metals ions have been studied and their suitability for radiation dosimetry applications is discussed. It was observed that this calcium aluminate phase doped with Tm-Cu at concentration of 0.1 mol% is a good candidate for dosimetric applications since it presents well-defined single peak observed at 240 °C and 320 °C and a linear response to gamma radiation dose from 5 × 10−3 Gy up to 100 Gy. 相似文献
16.
《Solid State Ionics》2006,177(13-14):1211-1217
La1−xSrxCr1−xMxO3−δ (M = Cr, Fe, V) system has been studied as anode materials for solid oxide fuel cells (SOFCs). The perovskite La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCM) is stable in both H2 and CH4 atmospheres at temperatures up to 1000°C. However, in the reducing atmospheres of H2 and CH4, its electronic conductivity is greatly reduced from its value in air. We have characterized LSCM as the anode of a SOFC having 250 μm-thick La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM) as the electrolyte and SrCo0.8Fe0.2O3−δ (SCF) as the cathode. We report a comparison of the overpotentials at the following anodes: (1) La0.4Ce0.6O1.8 (LDC) + NiO composite in H2, (2) porous LSCM in H2 and CH4, (3) porous LSCM impregnated with CuO in H2 and CH4 and (4) porous LSCM impregnated with CuO and sputtered with Pt in H2 and CH4. An LSCM + CuO + Pt anode gave a maximum power output at 850 °C of 850 mW/cm2 and 520 mW/cm2, respectively, with H2 and CH4 as fuel whereas anode (1) gave 1.4 W/cm2 at 800 °C in H2. There was no noticeable coke formation in CH4 with anodes (2), (3) and (4), which demonstrates that the perovskite oxide is a plausible option for the anode of a SOFC operating with hydrocarbon fuels. We also report the moisture effect in the H2 and CH4 fuel-oxidation process. 相似文献
17.
In pH 1.99 sodium acetate-HCl buffer solutions at 60 °C, Rhodamine B exhibited a strong fluorescence peak at 584 nm using
an excitation wavelength of 548 nm. The fluorescence quenching occurred when Fe3O4 nanoparticles catalyzed H2O2 oxidation of Rhodamine B. Under the chosen conditions, the fluorescence intensity at 584 nm decreased when the concentration
of H2O2 increased. The fluorescence quenching intensity is linear with the concentration of H2O2 in the range of 10–200 nmol/L. Thus, a new and simple and sensitive nanocatalytic fluorescence method was proposed for the
determination of H2O2 in synthetic sample, with satisfactory results. 相似文献
18.
The mobile Na+-ions (42/90 of the total) in Na5GdSi4O12 have been replaced by K+ ions in K-NaCl melts at 800°C. KxNa3?xGdSi3O9 (Na3GdSi3O9-type structure) was formed on the surface during immersion, and its quantity was found to be dependent on the (K+)/(Na+) ratio in the melt. Hydronium rare earth silicate was subsequently obtained by means of field-assisted ion exchange in acid. Dc resistivities for the hydronium rare earth silicates ((H3ONa)5GdSi4O12 and (H3ONa)5YSi4O12) were estimated as 1.8×107 and , respectively, at room temperature with activation energies of 0.49 eV and 0.77 eV between room temperature to 90°C. 相似文献
19.
Pigment-grade anatase TiO2 particles (160 nm) were passivated using ultra-thin insulating films deposited by molecular layer deposition (MLD). Trimethylaluminum
(TMA) and ethylene glycol (E.G) were used as aluminum alkoxide (alucone) precursors in the temperature range of 100–160 °C.
The growth rate varied from 0.5 nm/cycle at 100 °C to 0.35 nm/cycle at 160 °C. Methylene blue oxidation tests indicated that
the photoactivity of pigment-grade TiO2 particles was quenched after 20 cycles of alucone MLD film, which was comparable to 70 cycles of Al2O3 film deposited by atomic layer deposition (ALD). Alucone films would decompose in the presence of water at room temperature
and would form a more stable composite containing aluminum, which decreased the passivation effect on the photoactivity of
TiO2 particles. 相似文献
20.
Only a small amount (≤3.5 mol%) of Ge can be doped in Ga2O3, Ga1.4In0.6O3 and In2O3 by means of solid state reactions at 1400 °C. All these samples are optically transparent in the visible range, but Ge-doped Ga2O3 and Ga1.4In0.6O3 are insulating. Only Ge-doped In2O3 exhibits a significant decrease in resistivity, the resistivity decreasing further on thermal quenching and H2 reduction. The resistivity of 2.7% Ge-doped In2O3 after H2 reduction shows a metallic behavior, and a resistivity of ~1 mΩ cm at room temperature, comparable to that of Sn-doped In2O3. 相似文献