Mechanism for Electrochemical Oxidation of Highly Oriented Pyrolytic Graphite during Potential Cycling in Sulfuric Acid Solution

摘要

We investigated the electrochemical oxidation of highly oriented pyrolytic graphite (HOPG) during potential cycling in sulfuric acid solution to clarify the oxidation mechanism of carbon materials under dynamic operation conditions in polymer electrolyte fuel cells (PEFCs). The redox current peaks corresponding to hydroquinone-quinone reaction appeared on CVs following cycling between 0.6 and 0.8 V vs. NHE, suggesting that HOPG was partially oxidized to form surface functional groups, while it was hardly oxidized below 0.6 V. Ex-situ SEM observations show that the surface of HOPG became roughened with cycling between 0.6 and 0.8 V with formation an oxidized layer, whereas this oxidized layer became less stable in the course of gasification reaction involving CO{sub}2 and/or CO evolution in the potential ranges above 0.8 V. We discuss oxidation mechanism for HOPG corresponding to various potential ranges.