Topography, structure, and formation kinetic mechanism of carbon deposited onto nickel in the temperature range from 400 to 850°C
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The carbon deposition behavior on nickel particles was observed within the temperature range from 400 to 800°C in a pure methane atmosphere. The topography, properties, and molecular structure of the deposited carbon were investigated using field-emission scanning electron microscopy (FESEM), temperature-programmed oxidation (TPO) technology, X-ray diffraction (XRD), and Raman spectroscopy. The deposited carbon is present in the form of a film at 400–450°C, as fibers at 500–600°C, and as particles at 650–800°C. In addition, the structure of the deposited carbon becomes more ordered at higher temperatures because both the TPO peak temperature of deposited carbon and the Raman shift of the G band increase with the increase in experimental temperature, whereas the intensity ratio between the D bands and the G band decreases. An interesting observation is that the carbon deposition rate is suppressed in the medium-temperature range (M-T range) and the corresponding kinetic mechanism changes. Correspondingly, the FWHM of the G and D1 bands in the Raman spectrum reaches a maximum and the intensities of the D2, D3, and D4 bands decrease to low limits in the M-T range. These results indicate that carbon structure parameters exhibit two different tendencies with respect to varying temperature. Both of the two group parameters change dramatically as a peak function with increasing reaction temperature within the M-T range.
Keywordsnickel carbon deposition kinetic mechanisms solid oxide fuel cells
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This work was financially supported by the National Program on Key Basic Research Project of China (No. 2012CB215405), the China Postdoctoral Science Foundation (No. 2015M570036), and the National Natural Science Foundation of China (No. 51174022). The authors are immensely grateful to the kind help of Prof. Sridhar Seetharaman with the English writing.
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