Catalysis

Activation by oxidation and ligand exchange in a molecular manganese vanadium oxide water oxidation catalyst

Authors

Abstract

Despite their technological importance, reaction mechanisms of most water oxidation catalysts (WOCs) are poorly understood. We combine theoretical and experimental methods to reveal mechanistic insights into the reactivity of the highly active molecular WOC [Mn4V4O17(OAc)3]3-. Using density functional theory, electrochemistry and IR-spectroscopy, we propose a three-step activation mechanism: one-electron oxidation [Mn3+2Mn4+2]→[Mn3+Mn4+3], acetate-to-water ligand exchange, and another one-electron oxidation [Mn3+Mn4+3]→[Mn4+4]. Analysis of ligand exchange pathways shows that nucleophilic attack of water molecules along the Jahn-Teller axis of Mn3+ centers leads to lower activation barriers than attack at Mn4+ centers. Deprotonation of one water ligand by the leaving acetate group leads to formation of the activated species [Mn4V4O17(OAc)2(H2O)(OH)]1-. Computed Redox potentials are in excellent agreement with electrochemical measurements. This interplay between redox chemistry and ligand exchange controls the formation of the catalytically active species. These results provide key reactivity information essential to further study bio-inspired molecular WOCs and solid-state manganese oxide catalysts.

Content

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Supplementary material

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Supporting Information - Activation by oxidation and ligand exchange in a molecular manganese vanadium oxide water oxidation catalyst
Supporting Information for "Activation by oxidation and ligand exchange in a molecular manganese vanadium oxide water oxidation catalyst", including further information on Electrochemistry, Calculation of Ligand Exchange Pathways, and Calculation of Redox Potentials.
Thumbnail image of Mn4V4_Activation_Preprint_coord1.pdf
Coordinates - Activation by oxidation and ligand exchange in a molecular manganese vanadium oxide water oxidation catalyst
Coordinates for "Activation by oxidation and ligand exchange in a molecular manganese vanadium oxide water oxidation catalyst", including .xyz format coordinates of all optimized intermediates and transition states discussed in the manuscript and SI.