Carbon materials NEXAFS

For the electrocatalytic application of carbon materials, apart from their crys-talhnity and porosity, their surface chemistry is also of importance. XPS and NEXAFS are both capable of determining the surface functional groups on the carbon surface. In XPS, the sample is irradiated with X-rays ejecting photoelectrons into... 

Figure 7.6 C K-edge NEXAFS spectra of different carbon materials (J. Melke, unpublished results).

Depending on the final application of carbon materials, very different properties and structures on different length scales need to be analyzed in detail using the aforementioned methods and, most favorably, a combination of them. A systematic Raman, TEM, SEM, NEXAFS, and EPR study of various carbon materials for impregnation into carbon felts used as positive electrode in all-vanadium redox flow batteries is given by Melke et al. [14]. 

Braun, A., Mun, B. S., Huggins, F. E., and Huffman, G. P. (2007). Carbon speciation of diesel exhaust and urban particulate matter NIST standard reference materials with C(ls) NEXAFS spectroscopy. Environ. Sci. Technol. 41,173-178. 

In this example, a pentacene film was thermally evaporated to 50 nm thick on the native oxide of a room temperature silicon wafer. NEXAFS spectroscopy was performed on this film at the NIST/Dow soft x-ray materials characterization facility at the national synchrotron light source (NSLS) of Brookhaven National Laboratory. The carbon K-edge was collected at several incident angles, shown in Figure 4.2.5. 

The NEXAFS spectra of carbon-based materials are dominated by tt and a resonances [37]. The measurements are made in two modes (1) total electron yield... 

NEXAFS spectroscopy and microscopy provide a new approach to study carbon-based materials. During the last couple of years, nexafs microscopy has been successfully applied to materials characterization in a variety of fields ranging from polymer science andbiology to meteoritics (1,83,99). Here, the discussion is focused... 

Figure 10 Comparison of carbon K-edge near-edge spectra of carbonaceous materials synthesized using pillared clays as templates. The NEXAFS spectra were obtained by measuring the intensity of electron-yield with a bias of —100 eV to the entrance of the channeltron multiplier. Reproduced from [33] by permission from Elsevier.

In Chapter 7, the Raman and near-edge X-ray absorption fine structure (NEXAFS) techniques have been used by Sandi to investigate the electronic and structural properties of carbonaceous materials and those of electrodes made from the synthesized carbons. The electrochemical performance of the carbon anodes is compared and related to the electronic and structural features of the SEI layer. 

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