SEMINAR: School of Chemistry and Biochemistry Seminar
|School of Chemistry and Biochemistry Seminar : Water Oxidation Catalysts Inspired by Photosynthesis
Our group is interested in developing highly active water oxidation catalysts for incorporation into (photo)-electrochemical water splitting devices. Inspired by the only water oxidation catalyst known to be active in vivo, the Mn4Ca1O5 cluster found in Photosystem II (PSII), we initially imbedded tetranuclear Mn complexes into Nafion films and demonstrated sustained water oxidation catalysis in vitro on illumination with visible light and application of a bias.1 By combining these photoanodes with a ruthenium(II) sensitiser into a photo-electrochemical cell water oxidation was achieved using visible light as the only energy source, as occurs in PSII.2
Examination of the fate of the Mn cluster during catalysis using X-ray Absorption Spectroscopy (XAS) and Transmission Electron Microscopy (TEM) revealed that it dissociates in Nafion forming MnII species which, on application of a bias, are oxidized to MnOx nanoparticles (detected by TEM). These are reduced on illumination and O2 is concurrently released.3 Recent EPR studies support the catalytic cycle proposed from the XAS studies. Thus, water oxidation catalysis does not involve the original cluster. The observed cycling between photo-reduced MnII species and the Mn-oxide parallels the well-known biogeochemistry of Mn where MnIII/IV oxides, formed by oxidative processes, are photoreduced to Mn2+ in sunlight.
Given that catalysis did not involve the original Mn4O4 cluster, catalytic activity was expected to be independent of the Mn precursor. To our surprise, however, an examination of a series of Mn complexes found that the size, crystallinity and catalytic activity of the MnOx nanoparticles varied with precursor used to generate them. The presentation will also cover our recent research exploring various approaches for the deposition of catalytically active metal oxide films, including the application of ionic liquids.
Professor Leone Spiccia
Bayliss Building Lecture Theatre G33
Wed, 10 Oct 2012 12:00
Wed, 10 Oct 2012 13:00
Wed, 03 Oct 2012 15:33
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