The FeIV-O• oxyl unit as a key intermediate in water oxidation on the FeIII-hydroxide: DFT predictions

Aleksandr A. Shubin, Viktor Yu Kovalskii, Sergey Ph Ruzankin, Igor L. Zilberberg, Valentin N. Parmon, Felix N. Tomilin, Pavel V. Avramov

Research output: Contribution to journalArticlepeer-review

Abstract

The O-O coupling process in water oxidation on the gamma FeOOH hydroxide catalyst is simulated by means of density functional theory using model iron cubane cluster Fe4O4(OH)4. A key reactive intermediate is proposed to be the HO-FeIV-O• oxyl unit with terminal oxo radical. The “initial” vertex FeIII(OH) moiety forms this intermediate at the calculated overpotential of 0.93 V by adding one water molecule and withdrawing two proton–electron pairs. The O-O coupling goes via water nucleophilic attack on the oxyl oxygen to form the O-O bond with a remarkably low barrier of 11 kcal/mol. This process is far more effective than alternative scenario based on direct interaction of two ferryl FeIV-O sites (with estimated barrier of 36 kcal/mol) and is comparable with the coupling between terminal oxo center and three-coordinated lattice oxo center (12 kcal/mol barrier). The process of hydroxylation of terminal oxygen inhibits the O-O coupling. Nevertheless, being more effective for ferryl oxygen, the hydroxylation in fact enhances selectivity of the O-O coupling initiated by the oxyl oxygen.

Original languageEnglish
Article numbere26610
JournalInternational Journal of Quantum Chemistry
Volume121
Issue number10
DOIs
Publication statusPublished - 15 May 2021

Keywords

  • negative spin density
  • oxyl oxygen
  • the FeOOH hydroxide
  • the O-O coupling
  • water oxidation

OECD FOS+WOS

  • 1.04.EI CHEMISTRY, PHYSICAL
  • 1.01.PO MATHEMATICS, INTERDISCIPLINARY APPLICATIONS
  • 1.03.UH PHYSICS, ATOMIC, MOLECULAR & CHEMICAL
  • 1.03.UK PHYSICS, CONDENSED MATTER

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