title: Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution.
abstract: Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co(3+/4+) ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions.
authors.affiliation: Department of Chemistry, Chemical and Materials Engineering Division, Electrochemical Energy, Catalysis and Materials Science Laboratory, Technische Universität Berlin, Straße des 17. Juni 124, 10623 Berlin, Germany.
authors.forename: Arno
authors.initials: A
authors.lastname: Bergmann
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Elias
authors.initials: E
authors.lastname: Martinez-Moreno
authors.affiliation: Department of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, 14195 Berlin, Germany.
authors.forename: Detre
authors.initials: D
authors.lastname: Teschner
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Petko
authors.initials: P
authors.lastname: Chernev
authors.affiliation: Department of Chemistry, Chemical and Materials Engineering Division, Electrochemical Energy, Catalysis and Materials Science Laboratory, Technische Universität Berlin, Straße des 17. Juni 124, 10623 Berlin, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Gliech
authors.affiliation: Department of Chemistry, Chemical and Materials Engineering Division, Electrochemical Energy, Catalysis and Materials Science Laboratory, Technische Universität Berlin, Straße des 17. Juni 124, 10623 Berlin, Germany.
authors.forename: Jorge Ferreira
authors.initials: JF
authors.lastname: de Araújo
authors.affiliation: Department of Chemistry, Chemical and Materials Engineering Division, Electrochemical Energy, Catalysis and Materials Science Laboratory, Technische Universität Berlin, Straße des 17. Juni 124, 10623 Berlin, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Reier
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Dau
authors.affiliation: Department of Chemistry, Chemical and Materials Engineering Division, Electrochemical Energy, Catalysis and Materials Science Laboratory, Technische Universität Berlin, Straße des 17. Juni 124, 10623 Berlin, Germany.|Ertl Center for Electrochemistry and Catalysis, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
authors.forename: Peter
authors.initials: P
authors.lastname: Strasser