共查询到20条相似文献,搜索用时 406 毫秒
1.
Björn Wickman Maria Wesselmark Carina Lagergren Göran Lindbergh 《Electrochimica acta》2011,56(25):9496
Thin films of WOx and Pt on WOx were evaporated onto the microporous layer of a gas diffusion layer (GDL) and served as model electrodes in the polymer electrolyte fuel cell (PEFC) as well as in liquid electrolyte measurements. In order to study the effects of introducing WOx in PEFC electrodes, precise amounts of WOx (films ranging from 0 to 40 nm) with or without a top layer of Pt (3 nm) were prepared. The structure of the thin-film model electrodes was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy prior to the electrochemical investigations. The electrodes were analyzed by cyclic voltammetry and the electrocatalytic activity for hydrogen oxidation reaction (HOR) and CO oxidation was examined. The impact of Nafion in the electrode structure was examined by comparing samples with and without Nafion solution sprayed onto the electrode. Fuel cell measurements showed an increased amount of hydrogen tungsten bronzes formed for increasing WOx thicknesses and that Pt affected the intercalation/deintercalation process, but not the total amount of bronzes. The oxidation of pre-adsorbed CO was shifted to lower potentials for WOx containing electrodes, suggesting that Pt-WOx is a more CO-tolerant catalyst than Pt. For the HOR, Pt on thicker films of WOx showed an increased limiting current, most likely originating from the increased electrochemically active surface area due to proton conductivity and hydrogen permeability in the WOx film. From measurements in liquid electrolyte it was seen that the system behaved very differently compared to the fuel cell measurements. This exemplifies the large differences between the liquid electrolyte and fuel cell systems. The thin-film model electrodes are shown to be a very useful tool to study the effects of introducing new materials in the PEFC catalysts. The fact that a variety of different measurements can be performed with the same electrode structure is a particular strength. 相似文献
2.
M.H. Miles E.A. Klaus B.P. Gunn J.R. Locker W.E. Serafin S. Srinivasan 《Electrochimica acta》1978,23(6):521-526
Kinetic parametes were determined for the oxygen evolution reaction on 50–50 atom percent alloys of RuIr, RuPt, and IrPt and compared with results obtained using ruthenium, iridium, platinum, and RuO2/TiO2 electrodes. The potentiostatic studies were made on oxide covered electrodes at 80°C in both 1.0 M H2SO4 and 1.0 M CF3SO3H. Cyclic voltammetric studies showed that while these noble metals and alloys are about equally effective as electrocatalysts for the hydrogen evolution reaction, striking differences in activity are found for the oxygen evolution reaction. The order of electrocatalytic activity towards oxygen evolution in H2SO4 is Ru > RuIr alloy ~ RuO2/TiO2 ~ Ir > IrPt alloy > RuPt alloy > Pt. The type of acid used had very little effect on the kinetic parameters. The lower electrocatalytic activities when platinum is present is probably due to the formation of a platinum oxide film. The dual barrier model is used to interpret the results for the electrodes containing platinum. The best electrocatalysts for oxygen evolution in acid solutions consist of noble metals which form oxide films (RuO2, IrO2) possessing metallic characteristics. 相似文献
3.
High surface area tungsten oxide (WOx) based electrodes containing centers of Pt, Sn or Ru were synthesized. The WOx electrodes were found to display good capacitive behavior and relatively high specific capacitance values of up to 180 F g−1. The oxidation behavior of particularly HCOOH and (COOH)2, using the WOx electrodes containing Pt and Sn centers (Pt/WOx and Sn/WOx, respectively), was studied in detail in aqueous solutions at high potentials, i.e. at which O2 is evolved. Both HCOOH and (COOH)2 appear to be oxidized following 1st order kinetics. The (COOH)2 oxidation reaction is faster than the HCOOH reaction using otherwise the same experimental conditions. The reaction mechanism of both the HCOOH and (COOH)2 oxidation was found to most likely involve the adsorptive interaction of the two organics with the anode surface. The WOx based anodes appear to be promising catalysts for the anodic oxidation of both (COOH)2 and HCOOH. 相似文献
4.
The extent of irreversible deactivation of Pt towards hydrogen oxidation reaction (HOR) due to sulfur adsorption and subsequent electrochemical oxidation is quantified in a functional polymer electrolyte membrane (PEM) fuel cell. At 70 °C, sequential hydrogen sulfide (H2S) exposure and electrochemical oxidation experiments indicate that as much as 6% of total Pt sites are deactivated per monolayer sulfur adsorption at open-circuit potential of a PEM fuel cell followed by its removal. The extent of such deactivation is much higher when the electrode is exposed to H2S while the fuel cell is operating at a finite load, and is dependent on the local overpotential as well as the duration of exposure. Regardless of this deactivation, the H2/O2 polarization curves obtained on post-recovery electrodes do not show performance losses suggesting that such performance curves alone cannot be used to assess the extent of recovery due to sulfur poisoning. A concise mechanism for the adsorption and electro-oxidation of H2S on Pt anode is presented. H2S dissociatively adsorbs onto Pt as two different sulfur species and at intermediate oxidation potentials, undergoes electro-oxidation to sulfur and then to sulfur dioxide. This mechanism is validated by charge balances between hydrogen desorption and sulfur electro-oxidation on Pt. The ignition potential for sulfur oxidation decreases with increase in temperature, which coupled with faster electro-oxidation kinetics result in the easier removal of adsorbed sulfur at higher temperatures. Furthermore, the adsorption potential is found to influence sulfur coverage of an electrode exposed to H2S. As an implication, the local potential of a PEM fuel cell anode exposed to H2S contaminated fuel should be kept below the equilibrium potential for sulfur oxidation to prevent irreversible loss of Pt sites. 相似文献
5.
High surface area carbon-supported platinum-based catalysts, Pt/C, PtWO
x
/C, PtRu/C and PtRuWO
x
/C, were prepared via a chemical reduction route using single metal precursor salts. The catalyst particles were found to
be in the nanoscale range, and the addition of Ru clearly decreased the particle size. The Ru was found to be partially incorporated
into the face centered cubic lattice of Pt and to form a single Ru catalyst component. X-ray diffraction and X-ray photon
spectroscopy did not provide evidence for electronic interactions between WO
x
and Pt as well as WO
x
and Ru. However, the addition of tungsten to the PtRuWO
x
/C catalyst resulted in a high degree of catalyst particle agglomeration. Both Ru containing catalysts showed significantly
higher activities for the CH3OH oxidation reaction in terms of Pt + Ru mass as well as electroactive Pt + Ru surface area than the Pt/C and PtWO
x
/C catalysts. The addition of tungsten appeared to mainly result in some ‘physical’ modification of the catalytically active
Pt and Ru surface components such as differences in electroactive surface area rather than promotion of the CH3OH oxidation reaction via a true catalytic mechanism. 相似文献
6.
Tungsten oxide (WO3) nanocrystals with the diameter <5 nm supported on porous carbonized resin (denoted as C‐WO3) are synthesized. The WO3 precursors are dispersed at ion level through ion exchange route, then reduced to WO3 nanocrystals. Pt nanoparticles are loaded on the porous C‐WO3 matrix (denoted as Pt/C‐WO3) and used as electrocatalyst in fuel cell for alcohol oxidation, in which WO3 is found efficient promotion effect on Pt electrocatalyst in the electrochemical activity and stability. Thereinto, Pt/C‐WO3 gives 1.63 times higher current densities than the commercial Pt/C (TKK) for methanol oxidation at the same Pt loadings. Moreover, Pt/C‐WO3 electrocatalyst shows excellent properties in mass transfer than Pt/C (TKK). The present method can be readily scaled up for the production of other nanomaterials as well as WO3. 相似文献
7.
CO tolerance of H2-air single cell with phosphoric acid doped polybenzidazole (PA-PBI) membrane was studied in the temperature range 140-180 °C using either dry or humidified fuel. Fuel composition was varied from neat hydrogen to 67% (vol.) H2-33% CO mixtures. It was found that poisoning by CO of Pt/C and Pt-Ru/C hydrogen oxidation catalysts is mitigated by fuel humidification. Electrochemical hydrogen oxidation at Pt/C and Pt-Ru/C catalysts in the presence of up to 50% CO in dry or humidified H2-CO mixtures was studied in a cell driven mode at 180 °C. High CO tolerance of Pt/C and Pt-Ru/C catalysts in FC with PA-PBI membrane at 180 °C can be ascribed to combined action of two factors—reduced energy of CO adsorption at high temperature and removal of adsorbed CO from the catalyst surface by oxidation. Rate of electrochemical CO oxidation at Pt/C and Pt-Ru/C catalysts was measured in a cell driven mode in the temperature range 120-180 °C. Electrochemical CO oxidation might proceed via one of the reaction paths—direct electrochemical CO oxidation and water-gas shift reaction at the catalyst surface followed by electrochemical hydrogen oxidation stage. Steady state CO oxidation at Pt-Ru/C catalyst was demonstrated using CO-air single cell with Pt-Ru/C anode. At 180 °C maximum CO-air single cell power density was 17 mW cm−2 at cell voltage U = 0.18 V. 相似文献
8.
《Applied catalysis》1988,36(1):61-69
PtSn/Al2O3 catalysts, prepared by different deposition techniques and submitted to successive oxidation—reduction cycles at 500°C, were characterized by TPR and test reactions (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), and compared with fresh samples. Interpretation of the results is based on the fact that in catalysts obtained by both coimpregnation and successive impregnation, a higher quantity of PtSn alloys was produced as a consequence of the oxidation—reduction cycles. In catalysts prepared by impregnating the support with the [PtCl2(SnCl3)2]2− complex, the cycles produced changes in the metallic phase probably due to either a surface enrichment of tin in alloy particles or a modification of the alloy phase composition. 相似文献
9.
Binary and ternary anode catalyst formulations including the elements W, Sn and Mo for PEMFCs operated on methanol or reformate gas 总被引:1,自引:0,他引:1
In an exploratory approach to find improved electrocatalyst formulations binary and ternary carbon supported catalysts with the elements Pt and Ru, W, Mo or Sn, respectively, amending the choice of Pt and Pt/Ru catalysts by addition of non-Pt metal cocatalysts were manufactured by impregnation and a colloid method and tested towards their activity for anodic oxidation of H2 containing 150 ppm CO and of methanol. Membrane-electrode-assemblies with noble metal loadings of 0.4 mg cm−2 were manufactured and tested in fuel cell operation at 75°C with H2 fuel contaminated by CO and at 95°C for operation on methanol. Cocatalytic activities were found for the elements W and Mo for oxidation of H2/CO and methanol while in the case of Sn a cocatalytic activity was only found for H2/CO-oxidation. Both for oxidation of methanol and H2/CO the system Pt/Ru/W was superior to the other systems tested. The colloid method was found to be highly suitable for synthesizing polymetallic PEM catalysts. 相似文献
10.
《Fuel Processing Technology》2001,69(1):59-71
The effect of metal promoters on the activity and selectivity of tungstated zirconia (8 wt.% W) for n-hexadecane isomerization in a trickle bed continuous reactor is studied by using different metals (Pt, Ni, and Pd) and, in one case, by varying metal loading. Platinum is found to be the best promoter. The effect of hydrogen reduction is investigated using platinum-promoted tungstated zirconia catalysts (Pt/WO3/ZrO2, 0.5 wt.% Pt and 6.5 wt.% W). Pretreatment at temperatures between 300 and 400°C for 3 h in hydrogen is found to be slightly beneficial for achieving high yields of isohexadecane. A platinum promoted sulfated zirconia (Pt/SO4/ZrO2) is compared with a Pt/WO3/ZrO2 catalyst for the hydroisomerization of n-hexadecane in the same reactor at the same n-hexadecane conversion. The former is a good cracking catalyst and the latter is suitable for use as a hydroisomerization catalyst. In a 27-ml microautoclave reactor, studies of the hydroisomerization and hydrocracking of two Fischer–Tropsch (F–T) wax samples are carried out. Severe cracking can be effectively suppressed using a Pt/WO3/ZrO2 catalyst so as to obtain branched isomers in the diesel fuel or lube-base oil range. 相似文献
11.
Upendra A. Joshi James R. Darwent Humphrey H. P. Yiu Matthew J. Rosseinsky 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2011,86(8):1018-1023
BACKGROUND: This research investigated the effect of platinum (Pt) on the reactivity of tungsten oxide (WO3) for the visible light photocatalytic oxidation of dyes. RESULTS: Nanocrystalline tungsten oxide (WO3) photocatalysts were synthesised by a sol‐gel process and employed for the photocatalytic degradation of Methyl Orange under visible light. For comparison commercial bulk WO3 materials were also studied for the same reaction. These materials were fully characterised using X‐ray diffraction (XRD), UV‐visible diffuse reflection spectroscopy and transmission electron microscopy (TEM). The photocatalytic oxidation of iso‐propanol was used as a model reaction to follow the concomitant reduction of molecular oxygen. No reactions occured in the absence of platinum, which is an essential co‐catalyst for the multi‐electron reduction of oxygen. The platinised WO3 catalysts were stable for multiple oxidation–reduction cycles. The results from the catalytic activity measurements showed that platinised nanocrystalline WO3 is a superior oxidation photocatalyst when compared with bulk WO3. Methyl Orange was completely decolourised in 4 h. CONCLUSIONS: The enhanced performance of nanocrystalline Pt‐WO3 is attributed to improved charge separation in the nanosized photocatalyst. Platinum is an essential co‐catalyst to reduce oxygen. This photocatalyst could be applied to the treatment of organic pollutants in wastewater, with the advantage of using visible light compared with the widely studied TiO2, which requires UV light. Copyright © 2011 Society of Chemical Industry 相似文献
12.
《Fuel Processing Technology》1996,47(2):153-176
The reactions of 2,2′-dinaphthyl ether and diphenyl ether were studied at 375–425°C using 6.9 MPa (cold) hydrogen or nitrogen, 9,10-dihydrophenanthrene (DHP) and decalin as solvents, and a molybdenum sulfide catalyst. We chose to examine these compounds as models for the cleavage of diaryl ether bridges during coal liquefaction. The molybdenum sulfide was added to the reaction as MoS3, which should transform to the active MoS2 catalyst. Cleavage of the CarO in 2,2′-dinaphthyl ether, at reaction temperatures of 375 and 400°C, proceeded in the sequence H2 < DHPN2 < DHPH2 < DHPMoS3N2 < DHPMoS3H2 < MoS3H2 < Dec.MoS3H2. At 425°C, the MoS3H2 and Dec.MoS3H2 systems exchange places in this order. Diphenyl ether is less reactive than dinaphthyl ether toward hydrogenolysis reactions under these conditions. The conversion rate of diphenyl ether increases in the order H2 < DHPH2 < DHPMoS3N2 < DHPMoS3H2 < Dec.MoS3H2 < MoS3H2. Although the rates of conversion of the two ethers are different, the relative effects of using a reactive gaseous atmosphere, donor solvent, catalyst - or some combination of these factors - are the same for both compounds. In liquefaction experiments, hydrogen donor solvent or hydrogen shuttling solvent seems necessary to reduce retrogressive reactions. However, a solvent interacting strongly with catalyst and scavenging hydrogen atoms can reduce the activity of catalysts in hydrocracking reactions. 相似文献
13.
The current study is concerned with the preparation and characterization of tantalum oxide-loaded Pt (TaOx/Pt) electrodes for hydrogen spillover application. XPS, SEM, EDX and XRD techniques are used to characterize the TaOx/Pt surfaces. TaOx/Pt electrodes were prepared by galvanostatic electrodeposition of Ta on Pt from LiF-NaF (60:40 mol%) molten salts containing K2TaF7 (20 wt%) at 800 °C and then by annealing in air at various temperatures (200, 400 and 600 °C). The thus-fabricated TaOx/Pt electrodes were compared with the non-annealed Ta/Pt and the unmodified Pt electrodes for the hydrogen adsorption/desorption (Hads/Hdes) reaction. The oxidation of Ta to the stoichiometric oxide (Ta2O5) increases with increasing the annealing temperature as revealed from XPS and X-ray diffraction (XRD) measurements. The higher the annealing temperature the larger is the enhancement in the Hads/Hdes reaction at TaOx/Pt electrode. The extraordinary increase in the hydrogen adsorption/desorption at the electrode annealed at 600 °C is explained on the basis of a hydrogen spillover-reverse spillover mechanism. The hydrogen adsorption at the TaOx/Pt electrode is a diffusion-controlled process. 相似文献
14.
《Applied catalysis》1981,1(1-2):31-48
When Al2O3-, SiO2-, or TiO2-supported Pt catalysts were reduced above 400°C, there was a sharp decrease in their hydrogenolysis activity for n-pentane at 400°C. The chemisorption of H2 on the catalyst at 20°C also decreased as if a part of the surface Pt atoms was no longer accessible to chemisorption. A few air-H2 cycles at 20°C restored part of the hydrogenolysis activity and H2 chemisorption capacity lost on reduction of the catalyst at higher temperatures. An air oxidation at 500°C followed by reduction at 400°C fully restored the original properties of the catalyst. The uptake of hydrogen by oxidized catalysts above 400°C was more than would correspond to the topmost layer of the Pt surface only. In the case of Pt-TiO2, a reduction of the carrier was shown to occur at about 500°C by means of temperature-programmed desorption and reduction studies. The attenuation of the catalytic properties of the three types of catalysts studied seems to be caused mainly by a stronger chemisorption of H2 on Pt since such effects are observed on Pt-b1ack also. Self-inhibition by strongly chemisorbed H2 seems to be a widespread phenomenon in catalysis. 相似文献
15.
Georgeta Postole Simona Bennici Aline Auroux 《Applied catalysis. B, Environmental》2009,92(3-4):307-317
A major obstacle to the broader use of fuel cells is the poisoning of supported Pt catalysts by the CO present in virtually all feeds. In this paper, the microcalorimetry technique was employed to study and compare the CO adsorption properties of different commercial carbon-supported platinum catalysts with high Pt loading, aimed to be used in proton exchange membrane fuel cells (PEMFCs) applications. Combined with other techniques of characterization, such as BET, XRD, TPD-MS and TPR, adsorption microcalorimetry has permitted a better understanding of the studied systems. The pore architecture of Pt/C catalysts was found to influence the kinetics of heat release during CO adsorption. The accessibility of CO molecules to the adsorption sites increased with the mesoporosity of the catalyst. The degree of catalyst poisoning by CO upon successive air/H2/CO cycles varied between 2 and 30% for the different studied samples. These results confirm that the surface chemistry of the catalyst, and in particular the Pt deposition method, affects the surface site energy distribution and consequently the adsorptive properties towards H2 and CO. It was found that both H2 and CO are chemisorbed on the investigated samples. Pt/C powders exhibit higher differential heats of carbon monoxide adsorption in comparison with hydrogen adsorption. A reaction between pre-adsorbed H2 and CO from the gas phase takes place on Pt/C catalysts as a result of competitive adsorption. 相似文献
16.
Y. Hayakawa A. Kawashima H. Habazaki K. Asami K. Hashimoto 《Journal of Applied Electrochemistry》1992,22(11):1017-1024
Powder catalysts were prepared by immersion of amorphous Ni-40Zr and Ni-40Ti alloys containing a few at % of platinum group elements in HF solution. This treatment led to preferential dissolution of the valve metal and nickel with a consequent formation of microcrystalline alloy powders consisting of concentrated platinum group elements and some nickel and valve metal. Porous gas-diffusion electrodes prepared by using these alloy catalyst powders were employed for electrochemical reduction of oxygen and oxidation of hydrogen in 1 M H2SO4 at 25°C. The activity of the electrodes prepared from the amorphous alloys containing Pt–Ru, Pt–Rh, Pt and Pd for oxygen reduction was considerably higher than that of the platinum black electrode. Oxidation of hydrogen occurred readily close to the equilibrium potential. Amorphous alloy electrodes containing Pt–Ru, Pt–Rh and Pt were more active than the platinum black electrode for the hydrogen oxidation. 相似文献
17.
Xiaoxia Li Xinping Qiu Long Zhao Liquan Chen Wentao Zhu 《Journal of Applied Electrochemistry》2009,39(10):1779-1787
Different effects of support hydrophilicity and metal-oxide on the performance of Pt-based catalysts were investigated with
the aim of improving the mass activities toward methanol electrooxidation. Both potentiodynamic and potentiostatic measurements
revealed that improved surface hydrophilicity of multi-wall carbon nanotubes (MWCNTs) could promote the dispersion of Pt nanoparticles
and, consequently, promote the Pt utilization and reduce the polarization in methanol electrooxidation. In addition, WO3 was shown to play a supportive role in enhancing catalytic activity. The interaction between Pt and WO3 was examined by CO-stripping and CO oxidation transient experiments. The results suggested that the activity and the kinetics
of monolayer COads electrooxidation of Pt nanoparticles are enhanced by the adjacent WO3 via a bifunctional mechanism, which accounts for improved activity in methanol electrooxidation. 相似文献
18.
Masahiro Kitazawa Atsuko Y. Nosaka Yoshio Nosaka 《Journal of Applied Electrochemistry》2008,38(4):491-496
To clarify the deterioration mechanism for polymer electrolyte fuel cells, OH radical formation at the catalyst electrodes
was investigated by ESR (electron spin resonance) spectroscopy using a flow cell with the catalyst electrodes. OH radicals
produced from H2O2 were detected by a DMPO (5,5-dimethyl-1-pyrroline N-oxide) spin-trapping method for a Nafion-coated Pt/Carbon catalyst electrode
under a high potential (0.85 V versus RHE) on supplying H2 and under low potentials (lower than 0.40 V). When Pt–Ru catalysts were employed instead of Pt catalysts, the formation of
OH radicals was barely detected. The results suggest the possibility of the formation of OH radicals by the oxidation of H2O2 at the oxidized Pt surface under a positive potential as well as the reduction of H2O2 at the clean Pt surface under a low potential. 相似文献
19.
Effect of preparation conditions on the structure and catalytic activity of carbon-supported platinum for the electrooxidation of methanol 总被引:4,自引:0,他引:4
A. Stoyanova V. Naidenov K. Petrov I. Nikolov T. Vitanov E. Budevski 《Journal of Applied Electrochemistry》1999,29(10):1197-1203
Carbon-supported platinum catalysts (Pt/C) were prepared by treatment of PtO2/C under different conditions: (a) heating at 380°C in air, argon and hydrogen; (b) electrochemical reduction in H2SO4; and (c) reduction with NaBH4. The effect of the preparation conditions on the structure and the catalytic activity of the catalysts for the electrooxidation of CH3OH in acid media was studied. The highest activity was achieved for the catalyst treated in air. The activity is determined by the crystal faces exposed at the particle surface as well as particle size and the partial oxidation of the carbon support. 相似文献
20.
CO impedes the low temperature (<170 °C) oxidation of C3H6 on supported Pt. Supported Au catalysts are very effective in the removal of CO by oxidation, although it has little propene oxidation activity under these conditions. Addition of Au/TiO2 to Pt/Al2O3 either as a physical mixture or as a pre-catalyst removes the CO and lowers the light-off temperature (T
50) for C3H6 oxidation compared with Pt catalyst alone by ~54 °C in a feed of 1% CO, 400 ppm C3H6, 14% O2, 2% H2O. 相似文献