title: Surface oxide growth on platinum electrode in aqueous trifluoromethanesulfonic acid.
abstract: Platinum in the form of nanoparticles is the key and most expensive component of polymer electrolyte membrane fuel cells, while trifluoromethanesulfonic acid (CF3SO3H) is the smallest fluorinated sulfonic acid. Nafion, which acts as both electrolyte and separator in fuel cells, contains -CF2SO3H groups. Consequently, research on the electrochemical behaviour of Pt in aqueous CF3SO3H solutions creates important background knowledge that can benefit fuel cell development. In this contribution, Pt electro-oxidation is studied in 0.1 M aqueous CF3SO3H as a function of the polarization potential (E(p), 1.10 ≤ E(p) ≤ 1.50 V), polarization time (t(p), 10(0) ≤ t(p) ≤ 10(4) s), and temperature (T, 278 ≤ T ≤ 333 K). The critical thicknesses (X1), which determines the applicability of oxide growth theories, is determined and related to the oxide thickness (d(ox)). Because X1 > d(ox) for the entire range of E(p), t(p), and T values, the formation of Pt surface oxide follows the interfacial place-exchange or the metal cation escape mechanism. The mechanism of Pt electro-oxidation is revised and expanded by taking into account possible interactions of cations, anions, and water molecules with Pt. A modified kinetic equation for the interfacial place exchange is proposed. The application of the interfacial place-exchange and metal cation escape mechanisms leads to an estimation of the Pt(δ+)-O(δ-) surface dipole (μ(PtO)), and the potential drop (V(ox)) and electric field (E(ox)) within the oxide. The Pt-anion interactions affect the oxidation kinetics by indirectly influencing the electric field within the double layer and the surface oxide.
authors.affiliation: Nissan Research Center, Nissan Motor Co. Ltd., 1-Natsushima Cho, Yokosuka, Kanagawa 237-8523, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Furuya
authors.affiliation: Nissan Research Center, Nissan Motor Co. Ltd., 1-Natsushima Cho, Yokosuka, Kanagawa 237-8523, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Mashio
authors.affiliation: Nissan Research Center, Nissan Motor Co. Ltd., 1-Natsushima Cho, Yokosuka, Kanagawa 237-8523, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ohma
authors.affiliation: Nissan Technical Center North America, 39001 Sunrise Drive, Farmington Hills, Michigan 48331, USA.
authors.forename: Nilesh
authors.initials: N
authors.lastname: Dale
authors.affiliation: Nissan Technical Center North America, 39001 Sunrise Drive, Farmington Hills, Michigan 48331, USA.
authors.forename: Kenzo
authors.initials: K
authors.lastname: Oshihara
authors.affiliation: Department of Chemistry, Queen's University, 90 Bader Lane, Kingston, Ontario K7L 3N6, Canada.
authors.forename: Gregory
authors.initials: G
authors.lastname: Jerkiewicz