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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 64 (1992), S. 1871-1878 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A focused Cs+ beam was used to obtain secondary ion mass spectra and images from samples of stearic acid on gold before and after ablation by a beam of masive cluster ions. Ablation appears to have two effects on secondary ion emission. First, the number and intensity of peaks reflecting contamination are substantially reduced. Secondly, the absolute intensity of secondary ion current characteristic of the analyte increases. These features simplify mass spectra and improve contrast in the images obtained.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Over the last few years a number of fuel-cell power systems of various types and power outputs have been built by Shell Research Ltd. The first of these was a relatively primitive hydrazine-air system built in 1962. The paper will trace the development of these power systems from 1962 to the present day. Emphasis will be placed mainly on the engineering design and development that have been needed to take advantage of the improved catalysts and electrodes. Thus, the methods devised to give adequate fluid flows will be outlined, the simplification of components will be considered and the design of ancillaries will be discussed. Present-day fuel batteries have power densities of up to 130–150 W/kg (60–70 W/lb) and, even with commerically available auxiliaries, complete power systems having power/weight ratios of about 52 W/kg (24 W/lb) can be built. These figures are compared with the power densities of conventional electric generators, and future possibilities are discussed.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Pt/Sn electrodeposited catalysts have been prepared, characterized and tested for the electro-oxidation of methanol. Catalyst activities were measured in 3 M H2SO4 electrolyte between ambient temperature and 95°C. Enhancement in specific activity by a factor of about 50 was found over electrodeposited platinum black. This behaviour is in contrast to that of alloys of platinum and tin which were found to have very low activities compared with platinum catalysts and to be readily corroded in H2SO4 electrolyte. ESCA (electron spectroscopy for chemical analysis) studies and Mössbauer spectroscopy showed the majority of the tin in the deposit to be present in an oxidized form. A small amount (∼17%) was present as a dilute alloy of tin in platinum. Surface area measurements and X-ray powder diffraction indicated that the increase in activity over platinum black was not attributable to smaller platinum particle size. It seems that the combination of platinum and tin results in a decrease in the poisoning effect by strongly adsorbed organic residues. Whether this arises from the operation of a cyclic Sn(II)/Sn(IV) redox system or from modification of the platinum surface remains unresolved.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Trifluoromethanesulphonic acid monohydrate CF3SO3H.H2O and its aqueous solutions have been evaluated as an electrolyte for methanol electro-oxidation. The performances of conventional noble metal catalysts in the pure monohydrate are very poor compared with those in 3 M sulphuric acid. This is contrary to previously published literature data, and possible reasons for the discrepancy are given. In aqueous solutions of CF3SO3H at concentrations between 10 and 50%wt. considerably improved performance is obtained and at 60° C the activities of the catalysts are in most cases slightly higher than in 3 M H2SO4. In addition the poisoning effect of acid radicals is considerably less in CF3SO3H than in H2SO4 solutions. Above 60° C, however, the aqueous CF3SO3 anion decomposes to produce sulphur, which poisons the noble metal catalysts. Carbon-13 NMR studies of the CF3SO3H/H2O/CH3OH system were carried out at 20 and 37° C. From the results it was concluded that no significant ester formation occurred between CH3OH and CF3SO3H.H2O at these temperatures. Earlier published data on1H NMR studies of these solutions had indicated that 100% of the methanol was involved in ester formation with the acid. A critical analysis of this1H NMR work is given. Cyclic voltammetric characterization of catalysts in 10 and 25%wt. aqueous CF3SO3H solutions gave similar results to those in 3 M H2SO4; however, at concentrations of 50% wt. the acid decomposed at 0.0 V to produce a sulphur species that poisoned the catalyst. The conclusion of the work was that while aqueous CF3SO3H solutions produced promising catalyst performance up to 60° C the slight improvement in performance over 3 M H2SO4 would not offset the greater expense of the CF3SO3H. In addition, it was suspected that the long-term stability of the aqueous solutions even at 60° C might be poor.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The electrocatalytic aspects of direct oxidation of methanol in acid electrolyte in relation to fuel cell applications is briefly reviewed. The reaction requires noble metal catalysts (in particular platinum) in large quantities (several mg cm−2 of electrode area) to produce steady state current densities of commercial interest. Initial activities are about 104 times greater than steady state values, thus the problem in methanol electro-oxidation is to stabilize the initial activity. The approaches generally taken are to develop methods of dispersing platinum more effectively, e.g. by depositing the metal on a conducting support, or to modify the properties of platinum by alloying it with a second component. The latter approach can have the effect of simply isolating platinum atoms from each other, thus limiting the size of the platinum clusters, or of electronically modifying the properties of platinum by virtue of the ligand effect of the second component in the alloy. We have developed platinum and platinum-ruthenium catalysts supported on specially treated carbon-fibre paper which have substantially higher steady state activities than conventional catalysts. The method of preparation involves an ion-exchange procedure whereby noble metal cations become chemically bound to acidic surface oxide groups on the pre-oxidized carbon-paper surface. This produces platinum with increased surface area and high specific activity. It is proposed that the highly active form of platinum is involved in an interaction with the carbon support leading to improved performance. This modified form of platinum has been shown by cyclic voltammetry to have different characteristics of hydrogen adsorption/desorption and platinum oxide reduction from those of unsupported and conventionally supported platinum.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The influence of silicate and phosphate anions on the performance of Pt/Sn electrodeposited catalysts for the electro-oxidation of methanol has been studied. Both anions were found to have serious poisoning effects on the catalyst, whereas platinum catalysts were unaffected. The poisoning mechanism in both cases was thought to be initiated by the formation of either stannosilicates or stannophosphates species followed by the build-up of polymeric silicate or phosphate that ultimately blocks the active sites. The origin of the poisoning mechanism in both cases was found to be chemical rather than electrochemical. In the case of silicate, the poisoning species could be removed and the catalytic activity restored by chemical treatment with sulphuric acid.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Phosphoric acid and sulphuric acid have been compared as potential electrolytes for methanol-air fuel cells. The performances of typical electro-oxidation catalysts were measured in both electrolytes over a range of concentrations. With all catalysts the activity falls with increasing acid concentration. While this is to some extent due to the decrease in water activity at higher concentrations it seems that with both acids there is significant poisoning of the catalyst. The results can be explained for both electrolytes by assuming that adsorption of undissociated acid poisons the catalyst surfaces and that the reaction rate on the poisoned surfaces is proportional to the water activity.
    Type of Medium: Electronic Resource
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