Palladium Electrode in Oxygen‐Saturated Aqueous Solutions: Potential Dependent Adsorption of Oxygen Containing Species and Their Effect on Oxygen Reduction

Adsorption of oxygen species at palladium electrodes at various potentials, , was determined by a programmed potentiodynamic method in solutions of different p H. In all solutions examined, a linear relationship between and coverage,θ, with oxygen species was established in the range . An equation is obtained relating θ to and p H. This linear relationship extends from about vs. RHE to about 0.95V vs. RHE. This is the same potentials region in which the Tafel slope of −60 mV/dec has been reported for oxygen reduction at Pd electrodes. In view of the intermediated coverages, it is suggested that the first charge transfer under Temkin adsorption condition is the rate determining step for oxygen reduction. Fractional reaction orders with respect to H + , previously reported for the reduction in the Tafel region of −60 mV/dec, are now accounted for by the adsorption of oxygen species under Temkin conditions.