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Surface-oxide growth at platinum electrodes in aqueous H2SO4*1Reexamination of its mechanism through combined cyclic-voltammetry, electrochemical quartz-crystal nanobalance, and Auger electron spectroscopy measurements

2004; Elsevier BV; Volume: 49; Issue: 9-10 Linguagem: Inglês

10.1016/s0013-4686(03)00927-7

1873-3859

Gregory Jerkiewicz, Gholamreza Vatankhah, J. LESSARD, Manuel P. Soriaga, Yong Bae Park,

Gas Sensing Nanomaterials and Sensors

The mechanism of platinum surface electro-oxidation is examined by combined cyclic-voltammetry (CV), in situ electrochemical quartz-crystal nanobalance (EQCN) and ex situ Auger electron spectroscopy (AES) measurements. The CV, EQCN and AES data show that the charge density, interfacial mass variation and intensity of the O-to-Pt AES signal ratio increase in a continuous, almost linear manner as the potential is raised from 0.85 to 1.40 V. In addition, the charge density, mass variation and O-to-Pt signal ratio profiles follow each other, thus indicating that the surface oxidation proceeds by a progressive coordination of O-containing species to the Pt substrate. The coupled CV and EQCN measurements lead to in situ determination of the molecular weight of the interfacial species; these were identified as chemisorbed O (Ochem) at 0.85≤E≤1.10 V and as O2− in the form of a surface PtO at 1.20≤E≤1.40 V. The AES results reveal that the first half-monolayer of Ochem is formed through discharge of H2O molecules and such formed Ochem resides on the Pt surface. Subsequent discharge of H2O molecules leads to formation of the second half-monolayer of Ochem that is accompanied by the interfacial place exchange of Ochem and surface Pt atoms; this process results in the development of a quasi-3D surface PtO lattice comprising Pt2+ and O2−. AES data demonstrate that the place-exchange process occurs in the 1.10–1.20 V potential range. The experimentally determined molecular weight of the species added to the surface is 15.8 g mol−1, which points to O and to anhydrous PtO as the surface oxide formed.