title: Reactive oxygen species in iridium-based OER catalysts.
abstract: Tremendous effort has been devoted towards elucidating the fundamental reasons for the higher activity of hydrated amorphous IrIII/IVoxyhydroxides (IrOx) in the oxygen evolution reaction (OER) in comparison with their crystalline counterpart, rutile-type IrO2, by focusing on the metal oxidation state. Here we demonstrate that, through an analogy to photosystem II, the nature of this reactive species is not solely a property of the metal but is intimately tied to the electronic structure of oxygen. We use a combination of synchrotron-based X-ray photoemission and absorption spectroscopies,ab initiocalculations, and microcalorimetry to show that holes in the O 2p states in amorphous IrOxgive rise to a weakly bound oxygen that is extremely susceptible to nucleophilic attack, reacting stoichiometrically with CO already at room temperature. As such, we expect this species to play the critical role of the electrophilic oxygen involved in O-O bond formation in the electrocatalytic OER on IrOx. We propose that the dynamic nature of the Ir framework in amorphous IrOximparts the flexibility in Ir oxidation state required for the formation of this active electrophilic oxygen.
authors.affiliation: Department of Inorganic Chemistry , Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , Berlin , 14195 , Germany . Email: trjones@fhi-berlin.mpg.de; Catalysis for Energy , Group EM-GKAT , Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Elektronenspeicherring BESSY II , Albert-Einstein-Str. 15 , Berlin , 12489 , Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Pfeifer
authors.affiliation: Department of Inorganic Chemistry , Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , Berlin , 14195 , Germany . Email: trjones@fhi-berlin.mpg.de.
authors.forename: Travis E
authors.initials: TE
authors.lastname: Jones
authors.affiliation: Department of Inorganic Chemistry , Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , Berlin , 14195 , Germany . Email: trjones@fhi-berlin.mpg.de.
authors.forename: Sabine
authors.initials: S
authors.lastname: Wrabetz
authors.affiliation: Department of Inorganic Chemistry , Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , Berlin , 14195 , Germany . Email: trjones@fhi-berlin.mpg.de; Department of Heterogeneous Reactions , Max-Planck-Institut für Chemische Energiekonversion , Stiftstr. 34-36 , Mülheim a. d. Ruhr , 45470 , Germany.
authors.forename: Cyriac
authors.initials: C
authors.lastname: Massué
authors.affiliation: Department of Inorganic Chemistry , Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , Berlin , 14195 , Germany . Email: trjones@fhi-berlin.mpg.de; Department of Heterogeneous Reactions , Max-Planck-Institut für Chemische Energiekonversion , Stiftstr. 34-36 , Mülheim a. d. Ruhr , 45470 , Germany.
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Velasco Vélez
authors.affiliation: Diamond Light Source Ltd. , Harwell Science & Innovation Campus , Didcot , Oxfordshire OX 11 0DE , UK.
authors.forename: Rosa
authors.initials: R
authors.lastname: Arrigo
authors.affiliation: Department of Inorganic Chemistry , Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , Berlin , 14195 , Germany . Email: trjones@fhi-berlin.mpg.de; Department of Heterogeneous Reactions , Max-Planck-Institut für Chemische Energiekonversion , Stiftstr. 34-36 , Mülheim a. d. Ruhr , 45470 , Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Scherzer
authors.affiliation: Consiglio Nazionale delle Ricerche - Istituto Officina dei Materiali , c/o SISSA, Via Bonomea 265 , Trieste , 34136 , Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Piccinin
authors.affiliation: Department of Inorganic Chemistry , Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , Berlin , 14195 , Germany . Email: trjones@fhi-berlin.mpg.de; Department of Heterogeneous Reactions , Max-Planck-Institut für Chemische Energiekonversion , Stiftstr. 34-36 , Mülheim a. d. Ruhr , 45470 , Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Hävecker
authors.affiliation: Department of Inorganic Chemistry , Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , Berlin , 14195 , Germany . Email: trjones@fhi-berlin.mpg.de.
authors.forename: Axel
authors.initials: A
authors.lastname: Knop-Gericke
authors.affiliation: Department of Inorganic Chemistry , Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , Berlin , 14195 , Germany . Email: trjones@fhi-berlin.mpg.de; Department of Heterogeneous Reactions , Max-Planck-Institut für Chemische Energiekonversion , Stiftstr. 34-36 , Mülheim a. d. Ruhr , 45470 , Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Schlögl