title: Water-oxidation catalysis by manganese in a geochemical-like cycle.
abstract: Water oxidation in all oxygenic photosynthetic organisms is catalysed by the Mn₄CaO₄ cluster of Photosystem II. This cluster has inspired the development of synthetic manganese catalysts for solar energy production. A photoelectrochemical device, made by impregnating a synthetic tetranuclear-manganese cluster into a Nafion matrix, has been shown to achieve efficient water oxidation catalysis. We report here in situ X-ray absorption spectroscopy and transmission electron microscopy studies that demonstrate that this cluster dissociates into Mn(II) compounds in the Nafion, which are then reoxidized to form dispersed nanoparticles of a disordered Mn(III/IV)-oxide phase. Cycling between the photoreduced product and this mineral-like solid is responsible for the observed photochemical water-oxidation catalysis. The original manganese cluster serves only as a precursor to the catalytically active material. The behaviour of Mn in Nafion therefore parallels its broader biogeochemistry, which is also dominated by cycles of oxidation into solid Mn(III/IV) oxides followed by photoreduction to Mn²⁺.
authors: School of Chemistry and Australian Centre for Electromaterials Science, Monash University, Victoria 3800, Australia. Rosalie.Hocking@monash.edu
authors: Rosalie K
authors: RK
authors: Hocking
authors: Robin
authors: R
authors: Brimblecombe
authors: Lan-Yun
authors: LY
authors: Chang
authors: Archana
authors: A
authors: Singh
authors: Mun Hon
authors: MH
authors: Cheah
authors: Chris
authors: C
authors: Glover
authors: William H
authors: WH
authors: Casey
authors: Leone
authors: L
authors: Spiccia
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