Mechanism Of Oxygen Formation Research Articles

Degradation of iridium oxides via oxygen evolution from the lattice: correlating atomic scale structure with reaction mechanisms

Combination of atom probe tomography, isotope-labelling and online electrochemical mass spectrometry provides direct correlation of atomic scale structure of Ir oxide catalysts with the mechanism of oxygen formation from the lattice atoms.

Oxygen evolving reactions catalysed by manganese–oxo-complexes adsorbed on clays

A series of dinuclear manganese-oxo-complexes was prepared and adsorbed on kaolinite and montmorillonite clays. As indicated by UV-Vis spectroscopy, immobilization of the manganese compounds greatly altered the electronic properties due to strong interactions with the clay surfaces. When studied for their ability to catalyze oxygen formation upon reactions with the strong oxygen-transferring oxidants H(2)O(2) and oxone, it was found that surface adsorption yielded catalysts of improved performance for oxygen formation in aqueous media. Both the rates of oxygen evolution and catalyst stabilities were significantly increased for the clay hybrids of most complexes in comparison to homogeneous solutions of the compounds. Additionally, four heterogeneous systems were also found to catalyze the evolution of O(2) in reactions with the non-oxygen transferring, single- electron oxidation agent Ce(IV)--a reaction not observed for any dinuclear manganese complex in homogeneous reaction. Implications of these observations concerning the mechanism of oxygen formation and the development of manganese-based water oxidation catalysts are discussed.

Photooxidation of water by manganese(II) sulfate

The photoreduction of Mn(IV) sulfate in 6–10 M H2SO4 has been studied. The kinetics of the photoreaction are similar to that of the thermal oxidation of water by Mn(IV) sulfate. A strong dependence of the quantum yield on the energy of the absorbed quantum has been found. The mechanism of oxygen formation including decomposition of the “hot” dinuclear Mn complex is discussed.

ESR EVIDENCE FOR CHLOROPHYLL‐PHOTOSENSITIZED ONE‐ELECTRON OXIDATION OF WATER BY BENZOQUINONE*

Abstract—Illumination with red light of degassed solutions of chlorophyll and benzoquinone in dry acetone does not result in quinone radical formation, even though the presence of quinone greatly enhances the photoproduction of chlorophyll cation radical at low temperatures. However, when small amounts of water (or alcohols) are added to this system, large benzoquinone anion radical electron spin resonance (ESR) signals are generated. The effects on the low‐temperature ESR signals of microwave power saturation, replacement of chlorophyll and quinone by their deuterated analogs, and replacement of H2O by D2O, lead to the suggestion that a one‐electron oxidation of water is occurring. Pheophytin and bacteriochlorophyll are shown to sensitize a similar photoreaction. These results could lead to new insights into the mechanism of oxygen formation in photosynthesis.