Growth and Properties of Oxide Films on Platinum

Abstract

Electrocatalysts supporting the oxygen electrode reaction are commonly covered with thin oxide films that may have a profound influence over the kinetics of the reaction. Little is currently known about the role of oxide films on electrocatalysts, particularly with regard to the role of the defect structure. In this work, the physical and defect structures of the oxide film that forms on platinum in 0.5M normalH2SO4 under steady-state conditions have been investigated using electrochemical impedance spectroscopy (EIS) and ARXPS (angle-resolved X-ray photoelectron spectroscopy). Mott-Schottky analysis shows that the film is n-type, indicating that the defects in the film are either platinum interstitials or oxygen vacancies, or both. ARXPS analysis shows that, for potentials between 1.0 and 1.3normalVSHE , a single-layer film develops, with the principal oxidation state for Pt (in the film) being +2 . However, a bi-layer structure was observed for films formed at potentials greater than 1.3normalVSHE and ARXPS analysis shows that these bilayer films comprise an inner layer containing Pt(II) and an outer layer containing Pt(IV) . Optimization of the point defect model on the EIS data yields values for various kinetic parameters that are then used to predict the steady-state thickness and current. Good agreement with experiment is obtained.

Niobium addition enhancing the corrosion resistance of nanocrystalline Ti5Si3 coating in H2SO4 solution

“…MottSchottky analysis based on impedance measurements is a powerful in situ technique for assessing the electronic properties of the passive film. It has been used successfully in the past for the characterization of passive films formed on different passive materials [37,40,64]. According to semiconductor physical theory, the Mott-Schottky relationship expressing the potential dependence of the space charge capacitance C sc of a semiconductor film under depletion condition is described by Eq.…”

Atomistic Mechanism of Pt Extraction at Oxidized Surfaces: Insights from DFT

“…In addition, based on the in-situ electrochemical scanning tunneling microscopy (STM) observation, Wakisaka et al [23] have found that the irreversible morphological changes at Pt(111) occur predominantly during the reduction phase of oxide. The underlying process is sensitive to the formation of the socalled as α-oxide phase [24] that forms as a surface layer upon ramping up the potential to values above ∼1.1 V RHE [11].…”

Effect of Oxygen Evolution on Platinum Dissolution in Acidic Solution

“…9,11) Saturation may be attributed to the growth of the Pt oxide as the potential increases. 16,17) Above 1.55 V, the I C increased with E W to 1.75 V, after which it decreased. Thus, the initiation of the OER triggered the dissolution of Pt 4+ .…”

“…(4)), the interfacial place exchange of the adsorbed oxygen atoms with the top layer of the Pt atoms, and the formation of PtO 2 (eq. (5)), 13,16,17) as represented by the I W in the inset of Fig. 6(a).…”