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Issue 33, 2011
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Hydroxideoxidation and peroxide formation at embedded binuclear transition metal sites; TM = Cr, Mn, Fe, Co

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Abstract

Key steps in electro-catalytic water oxidation on binuclear Transition Metal (TM) sites are addressed. These comprise (a) two one-electron oxidation steps of TM–OH moieties to form the corresponding two TM[double bond, length as m-dash]O oxy-groups, and (b) a chemical step whereby the two oxy-species form a TM–O–O–TM peroxy-bridge. A test rig representing a generic low crystal field oxide support is described and employed. The energetics for homo-nuclear Cr(IIIV), Mn(IIIV), Fe(IIIV) and Co(IIIV) sites are compared. The uniqueness of the tyrosine/tyrosyl-radical (TyrOH/TyrO˙) reference potential for driving the oxidation steps is demonstrated. The oxidation of adsorbed TM–OH moieties on binuclear Mn and Co candidates requires an overpotential of approximately 0.5 V relative to the chosen reference potential. Correspondingly, the subsequent O–O bond formation becomes strongly exothermic, of the order of 1 eV. The hydroxide oxidation steps on binuclear CrCr and FeFe systems are, in total, exothermic by 1.21 and 0.61 eV, respectively, relative to the TyrOH/TyrO˙ reference potential. Consequently, the chemical step for transforming the TM[double bond, length as m-dash]O moieties to the peroxo species is found to be endothermic by the order of 0.7 eV. Based on these findings, a catalyst containing one TM from each class is suggested. The validity of this concept is demonstrated for the FeCo binuclear site. The results are discussed in the context of experimental observations, which display a preference for mixed oxide systems.

Graphical abstract: Hydroxide oxidation and peroxide formation at embedded binuclear transition metal sites; TM = Cr, Mn, Fe, Co

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Publication details

The article was received on 23 Feb 2011, accepted on 25 May 2011 and first published on 20 Jul 2011


Article type: Paper
DOI: 10.1039/C1CP20487D
Phys. Chem. Chem. Phys., 2011,13, 15062-15068

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    Hydroxide oxidation and peroxide formation at embedded binuclear transition metal sites; TM = Cr, Mn, Fe, Co

    M. Busch, E. Ahlberg and I. Panas, Phys. Chem. Chem. Phys., 2011, 13, 15062
    DOI: 10.1039/C1CP20487D

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