We investigated the electrochemical oxidation of highly oriented pyrolytic graphite (HOPG) in sulphuric acid solution under applying alternative potential pulses to elucidate the oxidation mechanism of carbon support of Pt/C catalyst under dynamic operation of polymer electrolyte fuel cells (PEFCs). After the potential pulse test between 0.6 and 1.0 V for 15 h, the capacitance of HOPG was increased and pits were found on the oxidised surface. With increase in the lower potential limit to 0.8 V, the increasing rate of capacitance was almost equal to that after holding at 1.0 V for 15 h, which suggests that carbon oxidation reaction could be accelerated in PEFCs by continual variation of the cell voltage. After the potential pulse test between 0.2 and 1.0 V, it was clarified that alcohol and carbonyl groups were accumulated on the surface of HOPG. The oxidation mechanism of HOPG under potential pulse condition was described.

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