Palladium Electrode in Oxygen‐Saturated Aqueous Solutions: Reduction of Oxygen in the Activation‐Controlled Region

Kinetics of electrochemical reduction of oxygen at oxide‐free palladium is studied using steady‐state galvanostatic technique. Measurements are taken in aqueous acid and alkaline solutions over a wide p H range and different oxygen partial pressures. relationships are characterized by two current density (c.d.) regions with distinctly different Tafel slopes. At low c.d.'s, the Tafel slope is close to −60 mV/decade, and, at high c.d.'s, to −120 mV/decade. The reaction order with respect to molecular oxygen is one in both c.d. regions in acid and alkaline solutions. In the high c.d. region, the reaction order with respect to is 1 in acid and 0 in alkaline solutions. In the low c.d. region, however, the reaction order with respect to is in acid and in alkaline solutions. These fractional reaction orders at Pd electrodes, reported here for the first time, are different than those reported in the literature. Possible causes for the difference are discussed. Mechanism of the reaction is suggested.