Hydrogen is considered to be an environmentally-friendly source of energy, because the only "waste product" from using it is water. However, for hydrogen to be truly non-polluting, it must be produced from renewable sources.
David Milstein (Weizmann Institute of Science, Israel) and coworkers have tackled this challenge. They have developed a process whereby water is split into hydrogen and water, using light and mild heat.
Hydrogen and oxygen generation.
The scientists' process is based on a catalyst molecule with a ruthenium metal center. Heating the catalyst in boiling water for three days generated hydrogen gas, H2, in 37% yield.
Subsequent illumination of the reacted catalyst with a 300 watt UV light for two days, under flowing argon gas, produced oxygen gas, O2, in 23% yield. Additionally, the catalyst was completely regenerated.
The scientists propose that hydrogen peroxide is initally produced under UV illumination, which is then catalytically converted into oxygen and water, without splitting the oxygen-oxygen bond. This is superficially reminiscent of the enzyme catalase, which performs a similar reaction millions of times per second.
Implications.
These scientists have developed a method to catalytically generate hydrogen gas and oxygen gas from water, using mild heat, UV light, and a catalyst molecule. The only "waste product" is water, and the catalyst is completely regenerated.
This means that hydrogen gas can now be efficiently produced from renewable sources. Remaining challenges include safely storing hydrogen, and efficiently utilizing energy obtained from it.
for more information:
Kohl, S. W.; Weiner, L.; Schwartsburd, L.; Konstantinovski, L.;
Shimon, L. J. W.; Ben-David, Y.; Iron, M. A.; Milstein, D.
Consecutive thermal H2 and light-induced O2
evolution from water promoted by a metal complex.
Science 2009, 324, 74-77.