Koordinationsverbindungen als potentielle Photokatalysatoren

SummaryWe describe a photochemical system for the generation of hydrogen by water reduction under visible light or sunlight irradiation of aqueous solutions containing the following components: a photosensitizer, the Ru (bipy):+ complex, for visible light absorption; a relay species, the Rh (bipy):+ complex, which mediates water reduction by intermediate storage of electrons via a reduced state; an electron donor, triethanolamine (TEOA) which provides the electrons for the reduction process and a redox catalyst, colloidal platinum, which facilitates hydrogen formation. The conditions for efficient hydrogen production and the influence of the concentration of the components have been investigated; the metal complexes act as catalysts with high turnover numbers; excess bipyridine facilitates the reaction. The process contains two catalytic cycles: a ruthenium cycle and a rhodium cycle. The Ru cycle involves oxidative quenching of the "Ru (bipy)pexcited state by Rh (bipy):+ forming Ru (bipy):+ which is converted back to Ru (bipy):+ by oxidation of the electron donor TEOA, which is thus consumed. The Rh cycle comprises a complicated set of transformations of the initial Rh (bipy):+ complex. The reduced rhodium complex formed in the quenching process undergoes a series of transformations involving the Rh (bipy); complex and hydridorhodiumbipyridine species, from which hydrogen is generated by reaction with the protons of water. In view of the storage of two electrons in the reduced rhodium species, the process is formally a dielectronic water reduction. The properties and eventual participation of [Rh (111) (bi~y)~LL']"+ (L, L'= H20, OH-) species are investigated. It is concluded that at neutral pH in presence of excess bipyridine, the cycle involving regeneration of the Rh (bipy):+ complex is predominant. A number of experiments have been performed with modified systems. Hydrogen evolution is observed with other photosensitizers (like proflavin), other relay species (like Rh (dimethylbipy):+ or Co (11)-bipyridine complexes), other donor species, or 4 (1979) -Nr. 142 in absence of the platinum catalyst. It also occurs in absence (of photosensitizer by sunlight or UV. irradiation of Rh(bipy):+ or by visible light irradiation of iridium (111)-bipyridine complexes. These systems deserve further investigations. The present photochemical hydrogen generating system represents the reductive component of a complete water splitting process. Its role in solar energy conversion and in photochemical fuel production is discussed.

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Koordinationsverbindungen als potentielle Photokatalysatoren

Cited by 23 publications

References 121 publications

Transition Metals in Photocatalysis

Transition Metals in Photocatalysis

Transition Metals in Photocatalysis

Hydrogen Generation by Visible Light Irradiation of Aqueous Solutions of Metal Complexes. An approach to the photochemical conversion and storage of solar energy

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