Structure of nitrogen-doped carbon spheres for energy applications

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  • Published: Apr 15, 2014
  • Author: Steve Down
  • Channels: X-ray Spectrometry / Raman
thumbnail image: Structure of nitrogen-doped carbon spheres for energy applications

The effects of nitrogen doping on the structures of carbon spheres prepared by the direct pyrolysis of methyl cyanide have been investigated by spectroscopic techniques.

Carbon spheres, as opposed to other elemental forms like tubes, fibres and horns, have been known for many years and have a wide variety of applications such as tyres, printer inks, batteries and memory devices. Now interest is growing in a modified form prepared by doping them with nitrogen because they have different properties and are being investigated in energy-related applications like fuel cells.

Despite this, there is much to be learnt about how nitrogen doping affects the structures of the spheres, so scientists from South Africa and the UK have taken a closer look, as they described in International Journal of Energy Research. Virgin carbon spheres and nitrogen-doped spheres were synthesised by the direct pyrolysis of acetylene in argon gas, or acetonitrile in argon/acetylene to produce spheres comprising concentric graphitic shells. The reactions were conducted in the absence of catalysts.

The introduction of nitrogen to the carbon spheres results in the formation of sp2 and sp3 carbon-nitrogen bonds as well as N-O/N2 bonds, confirmed by X-ray photoelectron spectroscopy. Raman spectroscopy revealed that the nitrogen atoms increased the number and/or size of the sp2 clusters. The amount of nitrogen that was incorporated depended on whether the pyrolysis was carried out in a vertical or horizontal reactor, which influenced the residence time. This will ultimately affect the properties of the nitrogen-doped spheres.

Both types of spheres also contained oxygen originating from their reaction with air after sphere formation. This can be removed if required by heating in argon but the presence of oxygen atoms helps with nitrogen functionalisation.

The nitrogen-doped carbon spheres could find application in devices such as magnetic data storage devices, oxidation-reduction catalysts, electric double layer capacitors and dye-sensitized solar cells.

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