The electrochemistry of graphite and modified graphite surfaces: the reduction of O2

Oxygen reduction to superoxide was examined in acetonitrile on the basal planes of ordinary and highly oriented pyrolytic graphite (OPG, HOPG). The reaction has a lower apparent cathodic transfer coefficient on HOPG than OPG, probably due to part of the potential drop across the electrode—electrolyte interface occurring in a space charge region in the HOPG. Oxygen reduction to peroxide was examined in aqueous alkaline solution on HOPG with adsorbed 9,10-phenanthrenequinone and on OPG with chemically attached 2-aminoanthraquinone. On the adsorbed quinone surface, the kinetics of the initial electron transfer (to the quinone) are fast while the reaction of reduced quinone with solution-phase O2 is the rate determining step. On the chemically attached quinone surface, the initial electron transfer is the rds because the quinone is further from the surface and in an unfavourable configuration for electron tunneling.