Dioxygen recent evolution 332

Very recently a new kind of electrocatalyst has been propounded using the dinuclear quinone-containing complex of ruthenium (25).492,493 Controlled-potential electrolysis of the complex at 1.70 V vs. Ag AgCl in H20 + CF3CH2OH evolves dioxygen with a current efficiency of 91% (21 turnovers). The turnover number of 02 evolution increases up to 33,500 when the electrolysis is carried out in water (pH 4.0) with an indium-tin oxide(ITO) electrode to which the complex is bound. It has been suggested that the four-electron oxidation of water is achieved by redox reactions of not only the two Run/Ruin couples, but also the two semiquinone/quinone couples of the molecule. 

Clearly, the S0 state must have one Mn(II), one Mn(III) and two Mn(IV) while the S4 must have three Mn(IV) and one Mn(V)—but where they are located in the tetra-Mn centre and how their four-electron reduction is coupled with water splitting and dioxygen evolution remains to be established. (For recent reviews see Goussias et al., 2002 Ferreira et al., 2004 Rutherford and Boussac, 2004 Iverson, 2006.)... 

Thus, most of the recent experimental data have been rationalized in terms of an active site that contains binuclear- or tetranuclear-manganese clusters with coordinated hydroxide ligands. The majority of the mechanisms for dioxygen evolution that are based on such models involve (1) sequential... 

Studies involving calcium and chloride have shown these ions to be critical to the proper functioning of the OEC (35, 146, 188), although their exact roles have yet to be elucidated. Without either of these, dioxygen evolution is halted and the OEC cannot complete one full cycle. It has recently been reported, for example, that the OEC can reach S2 without chloride, but cannot be further oxidized to S3 or pro-... 

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