Potential Energy Surface Profile of the Oxygen Reduction Reaction on a Pt Cluster: Adsorption and Decomposition of OOH and H2O2.

Because of their essential roles on determining pathways of the oxygen reduction reaction (ORR), the adsorption behavior and decomposition of the radical OOH and hydrogen peroxide on Pt clusters (Ptn, n = 3, 6, and 10) are extensively investigated using density functional theory. Two types of adsorption of the radical OOH on Pt clusters are found. One-end adsorbed hydrogen peroxide H2O2, arising from reduction of adsorbed OOH, is also located on Pt3, with an adsorption energy of -0.63 eV, suggesting that the ORR may proceed via a series pathway generating H2O2 as an intermediate. However, since OOH readily decomposes on Pt3 into atop adsorbed atomic oxygen and hydroxyl with an activation energy of only ∼0.25 eV, the OOR may take place preferentially via a direct pathway without H2O2 produced. A potential energy surface profile for the ORR is proposed, and the adsorption properties of other involved oxide species are characterized.