title: Direct observation of the dealloying process of a platinum-yttrium nanoparticle fuel cell cathode and its oxygenated species during the oxygen reduction reaction.
abstract: Size-selected 9 nm PtxY nanoparticles have recently shown an outstanding catalytic activity for the oxygen reduction reaction, representing a promising cathode catalyst for proton exchange membrane fuel cells (PEMFCs). Studying their electrochemical dealloying is a fundamental step towards the understanding of both their activity and stability. Herein, size-selected 9 nm PtxY nanoparticles have been deposited on the cathode side of a PEMFC specifically designed for in situ ambient pressure X-ray photoelectron spectroscopy (APXPS). The dealloying mechanism was followed in situ for the first time. It proceeds through the progressive oxidation of alloyed Y atoms, soon leading to the accumulation of Y(3+) cations at the cathode. Acid leaching with sulfuric acid is capable of accelerating the dealloying process and removing these Y(3+) cations which might cause long term degradation of the membrane. The use of APXPS under near operating conditions allowed observing the population of oxygenated surface species as a function of the electrochemical potential. Similar to the case of pure Pt nanoparticles, non-hydrated hydroxide plays a key role in the ORR catalytic process.
authors.affiliation: Center for Individual Nanoparticle Functionality (CINF), Department of Physics, Technical University of Denmark (DTU), DK-2800 Lyngby, Denmark. ibchork@fysik.dtu.dk.
authors.forename: Paolo
authors.initials: P
authors.lastname: Malacrida
authors.forename: Hernan G Sanchez
authors.initials: HG
authors.lastname: Casalongue
authors.forename: Federico
authors.initials: F
authors.lastname: Masini
authors.forename: Sarp
authors.initials: S
authors.lastname: Kaya
authors.forename: Patricia
authors.initials: P
authors.lastname: Hernández-Fernández
authors.forename: Davide
authors.initials: D
authors.lastname: Deiana
authors.forename: Hirohito
authors.initials: H
authors.lastname: Ogasawara
authors.forename: Ifan E L
authors.initials: IE
authors.lastname: Stephens
authors.forename: Anders
authors.initials: A
authors.lastname: Nilsson
authors.forename: Ib
authors.initials: I
authors.lastname: Chorkendorff