Redox Behavior of Pt/Co3O4(111) Model Electrocatalyst Studied by X-ray Photoelectron Spectroscopy Coupled with an Electrochemical Cell
Abstract
Achieving high stability of supported noble metal nanoparticles with respect to sintering is one of the major challenges in electrocatalysis. In this study, we explored the role of metal-support interaction in stabilizing the morphology of a well-defined model electrode consisting of Pt nanoparticles supported on well-ordered Co3O4(111) films on Ir(100).
We employed X-ray photoelectron spectroscopy coupled with an electrochemical cell to analyze changes in the oxidation states of both the supported Pt nanoparticles and Co3O4(111) support as a function of electrode potential. We found that immersion into the aqueous electrolyte at pH 10 (phosphate buffer) has no effect on the integrity and chemical composition of the Co3O4(111) film in a potential window between 0.5 and 1.4 V-RHE.
At lower potentials, reduction of the Co3O4(111) to Co(OH)(2) and metallic Co is accompanied by rapid dissolution of the film. In the presence of supported Pt particles, metal-support interaction gives rise to the formation of partially oxidized Pt delta+ species at the metal/oxide interface.
Under electrochemical conditions, these species are readily oxidized yielding platinum oxide at the Pt/Co3O4(111) interface at potentials as low as 0.5 V-RHE. The appearance of interfacial platinum oxide is accompanied by the formation of surface and bulk platinum oxides at potentials above 1.0 and 1.1 V-RHE, respectively.
While the formation and decomposition of surface and bulk platinum oxides depend on the electrode potential, the interface platinum oxide is stable between 0.5 and 1.4 V-RHE. We propose that the high stability of supported Pt nanoparticles with respect to sintering is associated with the presence of platinum interface oxide stabilized by the metal-support interaction.