Carbon corrosion scanning

Conductive polymers, such as polyacetylene, polythiophene, polypyrrole, polyisothianaphthene, polyethylene dioxythiophene, polyaniUne, and so on, have interesting properties that make them suitable for use in PEMFCs (Heeger, 2001 Shirakawa, 2001). Their electroconductivity and noncarbon functionalities allow some of them to perform effectively as alternative carbon catalysts or with carbon supports to enhance their catalytic effects. Huang et al. utilized polypyrrole as a conductive polymer support for a platinum catalyst active for the ORR (Huang et al., 2009). Their results show significant resistance to carbon corrosion and improved conductivity over traditional Pt/C catalysts. They report that the platinum on polypyrrole catalyst (Pt/Ppy) has well-dispersed platinum particles of about 3.6 nm in diameter. CV scans up to 1.8 V revealed that there was httle carbon support corrosion on the Pt/Ppy and a twofold increase in activity than Pt black at 0.9 V. 

One should keep in mind that carbon corrosion, especially in a later stage of the tests performed here, also may change the porous structure of the cathode catalyst layer concomitant with a void volume loss (Patterson and Darling 2006 Yu et al. 2006) and also with complete deterioration of the catalyst layer, which was confirmed by scanning electron microscopy postmortem analysis of the start-stop-cycled MEA. 

In an ideal cyclic voltammetric (CV) set-up, one would choose the appropriate scan rate and a potential window for scanning. In an aqueous electrolyte, one can scan the 1.5 V potential window to get mechanistic information, but in a real fuel cell, potentials above 0.75 V (vs. SHE) is not advised if the electro-active Pt is supported on carbon. At these elevated potentials, the carbon corrosion current density increases significantly and such a useful technique could impact the cell performance post diagnostics. Scan rates are typically... 

Scanning electron microscopic examinations of zinc samples exposed 1, 12, and 36 months showed extensive reorganization of the corrosion film through repeated cycles of dissolution and precipitation not unlike that which occurs on carbon steel and Cor-Ten A. 

Potentiodynamic polarization curves at two scan rates for carbon steel in boiling 4 N NaN03. Form of corrosion in different... 

B. Lin, R. Hu, C. Ye, Y. Li, C. Lin, A study on the initiation of pitting corrosion in carbon steel in chloride-containing media using scanning electrochemical probes, Electrochim. Acta 55 (2010)... 

M.J. Franklin, D.C. White, H.S. Isaacs, A study of carbon steel corrosion inhibition by phosphate ions and by an organic bnffer using a scanning vibrating electrode, Corros. Sci. 33 (1992) 251—260. 

M.J. Frankhn, D.C. White, H. Isaacs. Pitting corrosion by bacteria on carbon steel, determined by the scanning vibrating electrode technique. Corrosion Science, Vol. 32, No. 9, pp. 945-952, 1991. 

As is visible in Figure 4.14, a usage of 20 h is enough to produce an evident porosity of the dense layer also, an effect of superficial corrosion, due to the filamentous carbon, can be seen from the scanning electron microscopy (SEM) analysis (Galuszka et al., 1998). All the experimental evidence showed that these kinds of membranes are useful for the separation of methane and carbon monoxide-free streams, because while the swelling, due to hydrogen, can be controlled in a certain way, the same cannot be said for filamentous carbon formation. 

Franklin, M. J., Isaacs, H. S., and White, D. C., Pitting Corrosion by Bacteria on Carbon Steel Determined by the Scanning Vibrating Electrode Technique, Corrosion Science, Vol. 9, pp. 945-952. 

Uusitalo [150] analyzed iron sulfides via X-ray analysis to determine their influence on corrosion behavior. Tromans [151] conducted anodic polarization tests and used electron microscopy and including electron diffraction to reveal that sulfide incorporated into the Fe304 film impaired passivation. Honda et al. [152] performed extensive analysis of surface corrosion films in simulated liquor. Clarke and Singbeil [753] completed potentiodynamic polarization scans in white liquor, green liquor, and weak wash liquor at 90°C to investigate the effect of polysulfides on corrosion of carbon and stainless steels. 

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