The Role of Nanostructure in the Electrochemical Oxidation of Model-Carbon Materials in Acidic Environments

Carbon is ubiquitous in electrochemical energy devices and may exist in varied forms ranging from crystalline or amorphous to novel nanostructures based on a few sheets of graphene. The electrochemical oxidation of carbon results in the performance degradation of the electrochemical device. A study on the structure–reactivity relationship of the electrochemical oxidation of graphene-based carbon materials (carbon black, carbon onions, multiwalled nanotubes, and exfoliated graphite platelets) is presented. High resolution transmission electron microscopy, X-ray diffraction, elemental analysis, and adsorption were used to characterize the materials tested. Both liquid half-cell tests and proton exchange membrane fuel cell tests with inline carbon dioxide analysis were used to study the electrochemical behavior. The electrochemical oxidation of 10 seemingly disparate carbon materials was separated into two distinct mechanisms. Both mechanisms approach an 80% current efficiency for carbon dioxide formation. Iron and sulfur impurities are insignificant controlling factors. The difference between the two mechanisms is tentatively attributed to the degree of interlayer interaction between graphene sheets.