Making hydrogen gas in water just got a little easier. The discovery may lead to inexpensive, practical means of harvesting sunlight to create clean-burning hydrogen for powering cars or generating electricity.
Scientists would like to mimic plant photosynthesis, which harvests sunlight and splits water molecules to create fuel. It sounds simple, but even in plants the task is a highly orchestrated set of reactions, with multiple players acting in multiple places. So researchers often tackle one half of photosynthesis at a time.
The new study, published online November 8 in Science, focuses on the light-harvesting side of the equation. The researchers, from the University of Rochester in New York, created tiny particles of cadmium and selenium that spit out electrons when hit with light. The team also needed a catalyst to pass those electrons to hydrogen ions, which would combine into the useful gas H2.
Into their pot the researchers put water, the nanoparticles (along with a little chemical cap to make them soluble in water), a nickel catalyst and a few other ingredients. When light hit the nanocrystals the system chugged to life, generating hydrogen gas. And it didn’t stop. Often the light-absorbing part of such a system starts to degrade; when it breaks down, everything grinds to a halt.
“After two weeks it was still going like a champ,” says team member Todd Krauss. “We stopped it when we ran out of patience.”
In proper photosynthesis, the hydrogens that receive the electrons would come from splitting water, creating oxygen. The current setup doesn’t have a way to split water, so it uses another compound, ascorbic acid, to do water’s work.
The new setup overcomes several hurdles that can plague artificial photosynthesis efforts, says Stanford chemist Hemamala Karunadasa. The system is long-lasting and compatible with water, and the chemical players efficiently carry out more than one job.Not only that, the light-harvesting molecules can be tuned to capture energy from many wavelengths of light. “That’s nice, because sunlight has a lot of wavelengths,” she says.
Z. Han et al. Robust photogeneration of H2 in water using semiconductor nanocrystals and a nickel catalyst. Science. doi:10.1126/science.1227775.
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