The reduction of gaseous oxygen on carbon supported platinum electrodes has been studied at 150 degrees C with polarization and potential decay measurements. The electrolyte was either 100 weight percent phosphoric acid or that acid with a fluorinated additive, potassium perfluorohexanesulfonate (C6F13SO3K). The pseudo-Tafel curves of the overpotential vs. log (ii(L)/(i(L) - i)) show a two-slope behavior, probably due to different adsorption mechanisms. The potential relaxations as functions of log (t + tau) and log (-d eta/dt) have been plotted. The variations of these slopes and the dependence of the double-layer capacitance on the overpotential depended on the electrode manufacture and the kind of electrolyte (whether containing the fluorinated additive or not).
Journal of the Electrochemical Society, 1995, Vol 142, Issue 10, p. 3250-3256