X-ray absorption spectroscopy was used to identify specific types of nitrogen and sulfur-based carbon functionality present in the carbon black supports of fuel cell anodes and cathodes. The effects of these functional groups on the electrocatalytic performance of small platinum particles, dispersed on the carbon, during methanol oxidation and oxygen reduction were assessed. Electrodes functionalized with nitrogen had enhanced catalytic activities toward oxygen reduction and methanol oxidation relative to untreated electrodes. Although electrodes with sulfur functionality had higher oxygen reduction activities than untreated carbons, the activity of these electrodes toward methanol oxidation was found to be lower than electrodes manufactured from untreated carbon. It was found that carbon supports functionalized with both nitrogen and sulfur initiated the formation of Pt particles smaller in size than those observed on untreated carbon supports.