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  • 1995-1999  (4)
  • 1999  (4)
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  • 1995-1999  (4)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Characterization of polymers in PEFC-electrodes with EDX and XPS (1999)
    Springer
    Fresenius' journal of analytical chemistry 365 (1999), S. 123-132 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In polymer electrolyte fuel cells (PEFC) preferably Nafion® (Du Pont) is used as electrolyte material. The electrodes contain polytetrafluoroethylene (PTFE) as organic binder and the electrolyte Nafion® as additive to enlarge the three phase boundary zone. Since Nafion® is chemically related closely to PTFE, using surface analytical methods the two polymers can only be distinguished by the sulfonic acid groups in Nafion®. XPS measurements give information about the chemical composition of the electrode surface. By electron microscopy and EDX analysis it is possible to image the surface structure and to determine the local elements distribution, but hereby the distinction of the different polymers is a problem. In EDX spectra the sulfur peak induced from the sulfonic acid in the Nafion® is overlayed by a platinum peak from the catalyst component in the electrodes. Consequently, the distribution of the pure Nafion® cannot be determined by EDX. To make Nafion® distinguishable from PTFE and platinum the Nafion® in the electrode has to be marked, e.g. by exchange of the conducting protons in Nafion® by alkali ions like sodium. After having marked Nafion® its spatial distribution in fuel cell electrodes can be determined by EDX mapping of fluorine and sodium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160051457
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    XPS analysis of electrochemically oxidized nickel surfaces (1999)
    Springer
    Fresenius' journal of analytical chemistry 365 (1999), S. 154-157 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nickel, commonly used in electrochemical systems like batteries, fuel cells or as catalyst in alkaline water electrolysis can occur in different oxidation states. With surface analytical methods like X-ray photoelectron spectroscopy (XPS), it is possible to determine the oxidation state of metals. The application of this method requires that the sample is in an ultrahigh vacuum (UHV)-system. Therefore in-situ XPS-measurements of electrochemically oxidized samples are not possible. To avoid transfer through atmosphere one has to mount an electrochemical cell directly into a surface analytical system. By means of such an unit, nickel was polarized in potassium hydroxide solution (KOH) at different potentials. After that the different oxidation states were examined with XPS. The interpretation of these experiments is complicated because water is adsorbed after the electrochemical preparation. This can cause an additional surface layer. Ion-beam etching will not only remove this additional surface layer, it also changes the electrochemically prepared layer beyond. Comparing an electrochemically prepared single crystal with polycrystalline samples shows that the electrochemically prepared oxide layer is more clearly visible on the single crystal than on the polycrystalline material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160051463
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Potassium and oxygen diffusion and segregation in nickel (1999)
    Springer
    Fresenius' journal of analytical chemistry 365 (1999), S. 178-182 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nickel is used as catalyst in alkaline electrochemical systems like batteries, electrolyzers and fuel cells. Adsorption experiments from potassium on a thin NiO(100) epitactic layer on an Ag(100)-single crystal substrate showed that potassium intrudes in that NiO-layer where at a temperature of 350 K a mixed oxide phase was built. At 120 K metallic potassium was adsorbed on the NiO surface. A symmetric K2p-peak showed that potassium is in the oxidized state compared to the asymmetric peak of metallic potassium. No potassium diffused into metallic nickel at a temperature of 450 K. The electrochemically oxidized surface layer consisted of nickel, oxygen and also potassium. After heating and ion-etching no more potassium was detectable by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDX). But it was visible again after oxidizing and heating of the sample to 670 K. Therefore, the potassium must have been in the bulk. It diffused to the surface if there was oxygen at sufficiently high temperatures. Further heating reduces the surface and the potassium also disappeared.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160051468
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    XPS analysis of the degradation of Nafion (1999)
    Springer
    Fresenius' journal of analytical chemistry 365 (1999), S. 106-113 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In polymer membrane fuel cells (PEFC) Nafion® is frequently used as electrolyte membrane. Nafion® is an ion exchange polymer based on a PTFE backbone with added sulfonic acid groups. Before using in PEFC the Nafion® membrane is cleaned by a chemical pretreatment. The influence of this chemical pretreatment of Nafion® membranes was investigated with XPS measurements as well as the influence of electrochemical stressing. The Nafion® membrane will be decomposed during XPS measurements. X-ray exposure as well as ion etching induces a degradation of Nafion®. The change is related to a disintegration of the basis polymer PTFE as well as the sulfonic acid groups containing side chains. The decomposition of the side chains is faster than that of the PTFE backbone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160051454
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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