On the Effect of Electron Relay Redox Potential on Electron Transfer Reactions in a Water Photoreduction Model System

Israel Journal of Chemistry - Tập 22 Số 2 - Trang 117-124 - 1982
Edmond Amouyal1, Bertrand Zidler1
1Processus Photophysiques et Photochimiques, Bât. 350, Université Paris-Sud, 91405 Orsay, France

Tóm tắt

AbstractThe influence of electron relay redox potential (E1/2) on the electron‐transfer reactions occurring in the photo‐induced hydrogen generation from water has been investigated using the Ru(bipy)2+3/MV2+/EDTA/colloidal Pt model system. Quenching rate constants kq for electron transfer quenching of Ru(bipy)2+*3 by a series of 2,2′‐ and 4,4′‐bipyridinium ions and by a series of phenanthroline ions having different redox potential E1/2 have been determined by laser flash spectroscopy in deaerated aqueous solutions at pH 5. The rate constants kb of the back electron transfer following the quenching reaction have been obtained for five bipyridinium ions under the same experimental conditions. Our results show that: (1) for the same E1/2, the quencher molecular structure of the two homogeneous series does not affect kq significantly; (2) for the two series, kq increases with increasing E1/2 up to a value which is close to the diffusion‐controlled limit. The same correlation between kq and E1/2 is obtained for the two series. Such a correlation is satisfactorily interpreted in the frame of existing theories describing electron‐transfer reactions, particularly with the Rehm‐Weller treatment, provided that an intrinsic barrier ΔG*(0) = 5.2 kcal. M−1 is used; (3) kb is close to the diffusion‐controlled limit for E1/2 comprised between ‐ 0.33 and ‐ 0.65 V (vs NHE); (4) a correlation between H2 production rates and E1/2 is suggested, and a maximum H2 production is observed for E1/2 ≃ −0.45 V (vs. NHE) corresponding to compounds 1 and 14.

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Israel Journal of Chemistry

Tập 22 Số 2

117-124

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