Electrochemical oxidation of highly oriented pyrolytic graphite during potential cycling in sulfuric acid solution
Oxidation of highly oriented pyrolytic graphite (HOPG) under potential cycling conditions is investigated to understand the stability of graphite used in polymer electrolyte fuel cells (PEFCs) under their dynamic operation conditions. Electrochemical methods, AFM and XPS are applied to examine the surface oxidation of HOPG. The current peaks corresponding to quinone-hydroquinone redox reaction begin to appear on cyclic voltammograms after potential cycling between 0.6 V and 0.8 V vs. SHE (standard hydrogen electrode), indicating that the surface of HOPG is partially oxidized to form surface functional groups containing oxygen, whereas HOPG is relatively stable during potential cycling between 0.4 V and 0.6 V. An increase in potential range to 0.8-1.0 V extends the oxidation and forms pits on the surface of HOPG that is caused by the loss of surface carbon through the oxidation to gaseous products. The high rate of potential cycling accelerates the surface oxidation of HOPG.