New Insights into the Oxygen Reduction Reaction Mechanism on Pt (111): A Detailed Electrochemical Study

Abstract

The oxygen reduction reaction (ORR) is undoubtedly the most important fuel-cell cathodic reaction. In this work, a detailed electrochemical analysis of the ORR on Pt(111) in nonadsorbing electrolytes was performed, which included the high-potential region Eup =1.15 V while ensuring the electrode surface structure stability. Our results suggest that the reduction of a soluble intermediate species formed during the ORR is the rate-determining step in the whole reaction mechanism. This species does not undergo any other electrochemical reaction at E>0.9 V and may accumulate close to the electrode surface. Together with dissolved O₂, this intermediate may modify the oxide-growth dynamics on Pt(111). Hence, both species interact with the electrode surface through complex catalytic networks. Under certain experimental conditions, oxygenated species from the oxidation of Pt(111) may enhance the overall ORR current. These results propose an alternative to explain the current state of the art for this fundamental process.

Transient study of the oxygen reduction reaction on reduced Pt and Pt alloys microelectrodes: evidence for the reduction of pre-adsorbed oxygen species linked to dissolved oxygen

“…3 Figure 4c shows that dissolved oxygen in fact interacts with the Pt surface down to 0.85 V vs. RHE. Further comparison is however difficult since our study was conducted with polycrystalline Pt.…”

Oxygen reduction on nanostructured platinum surfaces in acidic media: Promoting effect of surface steps and ideal response of Pt(1 1 1)

“…Nevertheless, other works have suggested different reasons behind the lack of ORR reduction current for E > 1.0 V [19,36]. For example, it has been claimed that the reduction of an aqueous intermediate species is the RDS for the reaction [19]. Also, it has been proposed an effective 15 reversible potential for the oxygen four-electron reduction on Pt(111) of ~0.9 V, based on the exergonic O-O bond scission of the adsorbed hydroperoxyl radical OOH ads , being at least 0.9 eV exergonic [36].…”

“…10 In consequence, results from this work, do not support the idea about the O ads , or OH ads , removal as the rate determining step for the ORR. Nevertheless, other works have suggested different reasons behind the lack of ORR reduction current for E > 1.0 V [19,36]. For example, it has been claimed that the reduction of an aqueous intermediate species is the RDS for the reaction [19].…”

Oxygen reduction on a Pt(111) catalyst in HT-PEM fuel cells by density functional theory

“…Pt(111) surface is the most active compared to other surface. 34,35 Then, the Pt(111) surface was cut from the optimized Pt primitive cell. 41 To develop a super cell as a geometric model system, four layers of Pt atoms were placed in this system; the lowest two layers were restrained on the bottom of this system, and a vacuum thickness of 2.0 nm was set up above the Pt atoms (Fig.…”

“…31 Because the catalytic activity of the Pt(111) surface is higher than that of other Pt surfaces, 32,33 the Pt(111) surface is considered to be the one that most readily adsorbs the oxygen molecule. 34,35 First-principle mechanism and its density functional theory are often used in the electrochemical modeling of the oxygen reduction reaction on Pt(111). [36][37][38] In a previous study that used the density functional theory method, the electric field and solvent were considered as factors that influence the oxygen reduction reaction on Pt(111).…”