OXYGEN REDUCTION ON GAS-DIFFUSION ELECTRODES FOR PHOSPHORIC-ACID FUEL-CELLS BY A POTENTIAL DECAY METHOD

The reduction of gaseous oxygen on carbon supported platinum electrode s has been studied at 150 degrees C with polarization and potential de cay measurements. The electrolyte was either 100 weight percent phosph oric acid or that acid with a fluorinated additive, potassium perfluor ohexanesulfonate (C6F13SO3K). The pseudo-Tafel curves of the overpoten tial vs. log (ii(L)/(i(L) - i)) show a two-slope behavior, probably du e to different adsorption mechanisms. The potential relaxations as fun ctions of log (t + tau) and log (-d eta/dt) have been plotted. The var iations of these slopes and the dependence of the double-layer capacit ance on the overpotential depended on the electrode manufacture and th e kind of electrolyte (whether containing the fluorinated additive or not).