The Dissociation and Reduction of Molecular Oxygen on Platinum, Palladium, Iridium, Rhodium, and Gold

A method for electrochemically investigating the oxygen dissociation on various metals is presented, enabling the determination of the acidic oxygen reduction reaction path. The analysis reveals that molecular oxygen rapidly dissociates chemically into oxygen species on platinum, palladium, iridium, and rhodium surfaces. This is evidenced by the formation of electrochemically active surface oxygen species without charge transfer through. These species are subsequently electrochemically reduced to water. By analyzing the combined surface charge of these species across different metals, a step-by-step microkinetic model of the ORR is developed alongside the introduction of an alternative to the Langmuir-, Frumkin-, and Temkin model for the coverage of surface oxygen to rationalize the open circuit potential. This framework accurately reproduce experimental ORR activities and characteristics, explains deviations of the expected reversible oxygen potential, predicts the Volcano relationship across different metals, and distinguishes a reversible and quasi-reversible region of the oxygen reduction reaction.