Photocatalytic reduction of water to hydrogen using ruthenium(II) polypyridine photosensitizers and a cobalt dimethylglyoximato water reduction catalyst.

摘要

The photochemical production of dihydrogen from water is a vital route for converting solar energy into chemical energy. This has great importance in the development of technology for renewable energy sources. We will discuss molecular systems by which this conversion from light energy into chemical potential energy in the form of dihydrogen has been accomplished. These systems are comprised of a light absorber, and a water reduction catalyst, and sacrificial electron donor. We have synthesized and characterized spectroscopically, spectrometrically and using DFT computational methods a series of ruthenium(II) polypyridyl compounds which operate as light harvesting compounds. The water reduction catalyst is a cobalt dimethylglyoximato complex which is either pre-synthesized, or generated in situ. Upon photoexcitation, the light absorber transfers an electron to the cobalt based water reduction catalyst during various steps in the catalytic cycle. The mechanism by which the cobalt catalyst operates is studied by DFT methods, and provides insight into the limitations of elucidating the mechanism spectroscopically, as well as to indicate changes to the catalyst system which may allow it to operate more efficiently. We will discuss the system used to measure hydrogen production, as well as some interesting observations made while optimizing conditions, to maximize hydrogen production and increase long-term stability, including questions regarding the structure of the active catalyst.