ChemInform Abstract: Cobalt(III) Complexes Containing Incomplete Co3O4 or Complete Co4O4 Cubane Core

Ama, Tomoharu; Rashid, Md. M.; Yonemura, Toshiaki; Kawaguchi, Hiroshi; Yasui, Takaji

doi:10.1002/chin.200027251

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“…It was proposed in previous studies of amorphous CoCat catalyst films 30 that the OER active sites are di-µ-oxo-bridged (µ2-O) ion clusters, in which Co atoms are in a nearoctahedral coordination by 6 oxygen ligands with a Co-Co distance is 2.81 Å and oxygen atoms bound to two Co atoms only, a configuration which is similar to that in Co-oxo cubanes. 54 On the (001) plane of CoOOH, only µ3-O/OH sites exist, where the oxygen is threefold coordinated to Co 3+ , and µ2-O configurations only exist at steps of CoOOH(100) surface or near Co 3+ surface vacancies (Figure 6). According to our structural data, the coverage of µ2-O/OH sites on our CoOOH is only a few percent.…”

Section: Catalytic Properties and Structure Of Active Sitesmentioning

confidence: 99%

Operando Surface X-ray Diffraction Studies of Structurally Defined Co₃O₄ and CoOOH Thin Films during Oxygen Evolution

et al. 2019

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In the search for precious-metal free electrode materials for electrochemical water splitting, transition metal oxides have been receiving much recent interest as active and stable electrocatalysts for the anodic oxygen evolution reaction (OER). We present operando surface X-ray diffraction studies of two structurally well-defined epitaxial cobalt oxide thin films -Co3O4(111) and CoOOH(001) electrodeposited on Au(111). The potential-dependent structural changes during cyclic voltammograms were monitored with high time resolution up to OER current densities as high as 150 mA cm -2 . The CoOOH(001) film is found to be smooth and perfectly stable over a wide potential range. In the case of Co3O4(111), fast and fully reversible structural changes are observed. Specifically, the surface region of Co3O4( 111) starts restructuring at potentials 300 mV negative of the onset of the OER, indicating that the process is related to the thermodynamically predicted Co3O4 / CoOOH(001) transition rather than to the catalytic reaction. The formed skin layer is of defined thickness, which changes linearly with applied potential, and is the OER active phase. Surprisingly, the catalytic activity of the skin layer covered Co3O4 film and that of the smooth CoOOH(001) are almost identical, if the true microscopic surface area is taken into account.This indicates that the number of OER active sites on the two oxides is similar, despite the very different defect density, and is at variance with previous suggestions that di-µ-oxo bridged Co cations are exclusively responsible for the OER activity of Co oxides. For the smooth CoOOH(001) a turnover frequency of 4.2 s -1 per surface atom is determined at an overpotential of 400 mV. Furthermore, our studies demonstrate that the pseudo-capacitive charging current in the pre-OER potential range must be assigned to a bulk process that is accompanied by potential-dependent changes of the unit cell volume in the Co3O4 bulk.

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Section: Catalytic Properties and Structure Of Active Sitesmentioning

confidence: 99%

Operando Surface X-ray Diffraction Studies of Structurally Defined Co₃O₄ and CoOOH Thin Films during Oxygen Evolution

et al. 2019

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ChemInform Abstract: Cobalt(III) Complexes Containing Incomplete Co₃O₄ or Complete Co₄O₄ Cubane Core

Cited by 1 publication

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Operando Surface X-ray Diffraction Studies of Structurally Defined Co₃O₄ and CoOOH Thin Films during Oxygen Evolution

Operando Surface X-ray Diffraction Studies of Structurally Defined Co₃O₄ and CoOOH Thin Films during Oxygen Evolution

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ChemInform Abstract: Cobalt(III) Complexes Containing Incomplete Co3O4 or Complete Co4O4 Cubane Core

Cited by 1 publication

References 1 publication

Operando Surface X-ray Diffraction Studies of Structurally Defined Co3O4 and CoOOH Thin Films during Oxygen Evolution

Operando Surface X-ray Diffraction Studies of Structurally Defined Co3O4 and CoOOH Thin Films during Oxygen Evolution

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ChemInform Abstract: Cobalt(III) Complexes Containing Incomplete Co₃O₄ or Complete Co₄O₄ Cubane Core

Operando Surface X-ray Diffraction Studies of Structurally Defined Co₃O₄ and CoOOH Thin Films during Oxygen Evolution

Operando Surface X-ray Diffraction Studies of Structurally Defined Co₃O₄ and CoOOH Thin Films during Oxygen Evolution