title: Electrosynthesis of Biomimetic Manganese-Calcium Oxides for Water Oxidation Catalysis--Atomic Structure and Functionality.
abstract: Water-oxidizing calcium-manganese oxides, which mimic the inorganic core of the biological catalyst, were synthesized and structurally characterized by X-ray absorption spectroscopy at the manganese and calcium K edges. The amorphous, birnesite-type oxides are obtained through a simple protocol that involves electrodeposition followed by active-site creation through annealing at moderate temperatures. Calcium ions are inessential, but tune the electrocatalytic properties. For increasing calcium/manganese molar ratios, both Tafel slopes and exchange current densities decrease gradually, resulting in optimal catalytic performance at calcium/manganese molar ratios of close to 10 %. Tracking UV/Vis absorption changes during electrochemical operation suggests that inactive oxides reach their highest, all-Mn(IV) oxidation state at comparably low electrode potentials. The ability to undergo redox transitions and the presence of a minor fraction of Mn(III) ions at catalytic potentials is identified as a prerequisite for catalytic activity.
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
authors.forename: Diego
authors.initials: D
authors.lastname: González-Flores
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
authors.forename: Ivelina
authors.initials: I
authors.lastname: Zaharieva
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Heidkamp
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 Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
authors.forename: Elías
authors.initials: E
authors.lastname: Martínez-Moreno
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
authors.forename: Chiara
authors.initials: C
authors.lastname: Pasquini
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Mohammadi
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Klingan
authors.affiliation: Technical University Berlin, Department of Chemistry, Straße des 17. Juni 135, 10623, Berlin, Germany.|Institute of Inorganic and Analytical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse 21, 76104, Freiburg, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Gernet
authors.affiliation: Technical University Berlin, Department of Chemistry, Straße des 17. Juni 135, 10623, Berlin, Germany.|Institute of Inorganic and Analytical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse 21, 76104, Freiburg, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Fischer
authors.affiliation: Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany. holger.dau@fu-berlin.de.
authors.forename: Holger
authors.initials: H
authors.lastname: Dau
mesh_terms: D032701:Biomimetics; D002118:Calcium / Q000737:chemistry*; D002384:Catalysis; D004563:Electrochemistry; D008345:Manganese / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D014867:Water; D008345:Manganese; D002118:Calcium
keywords: calcium; electrochemistry; manganese; oxidation; water chemistry