ScienceDaily (Apr. 8, 2009) — The design of efficient systems for splitting water into hydrogen and oxygen, driven by sunlight is among the most important challenges facing science today, underpinning the long term potential of hydrogen as a clean, sustainable fuel. But man-made systems that exist today are very inefficient and often require additional use of sacrificial chemical agents. In this context, it is important to establish new mechanisms by which water splitting can take place
The new approach that the Weizmann team has recently devised is divided into a sequence of reactions, which leads to the liberation of hydrogen and oxygen in consecutive thermal- and light-driven steps, mediated by a unique ingredient – a special metal complex that Milstein’s team designed in previous studies. Moreover, the one that they designed – a metal complex of the element ruthenium – is a ‘smart’ complex in which the metal center and the organic part attached to it cooperate in the cleavage of the water molecule.
The team found that upon mixing this complex with water the bonds between the hydrogen and oxygen atoms break, with one hydrogen atom ending up binding to its organic part, while the remaining hydrogen and oxygen atoms (OH group) bind to its metal center.
This modified version of the complex provides the basis for the next stage of the process: the ‘heat stage.’ When the water solution is heated to 100 degrees C, hydrogen gas is released from the complex – a potential source of clean fuel – and another OH group is added to the metal center.
‘But the most interesting part is the third ‘light stage,’’ says Milstein. ‘When we exposed this third complex to light at room temperature, not only was oxygen gas produced, but the metal complex also reverted back to its original state, which could be recycled for use in further reactions.’
more:
http://www.sciencedaily.com/releases/2009/04/090406102555.htm
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