Carbon spheres for energy applications: Raman and X-ray photoemission spectroscopy studies

The effect of nitrogen functionalization on the atomic structure of carbon spheres (CSs) with diameters similar to 55-900 nm, made via direct pyrolysis process, has been studied. The CSs and NCSs were made in a tubular quartz reactor placed either in a vertical furnace or in a horizontal furnace. The chemical bonding in the CSs and NCSs was investigated by means of X-ray photoelectron (XPS) and Raman spectroscopies. XPS studies revealed a decrease in the sp(3) bonded carbon sites and an associated increase in the N-sp(2)C bonding sites after nitrogenation. These results were further confirmed by Raman spectroscopy that showed that the I-D/I-G ratio increased after N addition to the spheres, indicating a rise in either the number or size of the sp(2) clusters. In addition, scanning electron microscopy showed that the spheres, which are >90 at% carbon, consist of concentric graphitic shells. The possible use of CSs in magnetic data storage devices, oxygen reduction reactions, electric double layer capacitors and dye-sensitized solar cells to generate clean and sustainable energy technologies is described. Copyright (c) 2013 John Wiley & Sons, Ltd.