Energy from light and water: New photocatalytic method for the clean production of hydrogen from water
February 9, 2010(PhysOrg.com) -- Hydrogen-powered fuel cells and solar energy are the best hope for a more environmentally friendly and resource-sparing energy supply in the future. A combination of the two is considered to be particularly “clean”: the production of hydrogen by splitting water with sunlight. Previous approaches to this have suffered from high costs and the limited lifetime of their catalytic systems.
In the journal Angewandte Chemie, a team led by Thomas Nann and Christopher J. Pickett at the University of East Anglia (Norwich, UK) has now introduced an efficient, robust photoelectrode made of common, inexpensive materials.
The new system consists of a gold electrode that is covered with layers of indium phosphide (InP) nanoparticles. The researchers then introduce an iron-sulfur complex, [Fe2S2(CO)6], into the layered arrangement. When submerged in water and irradiated with light under a relatively small electric current, this photoelectrocatalytic system produces hydrogen with an efficiency of 60%. “This relatively high efficiency is a breakthrough,” says Nann.
The researchers have proposed the following mechanism for the reaction: The incoming light particles are absorbed by the InP nanocrystals and excite electrons within the InP. In this excited state, the electrons can be transferred to the iron-sulfur complexes. In a catalytic reaction, the iron-sulfur complexes then pass their electrons on to hydrogen ions (H+) in the surrounding water, which are then released in the form of hydrogen (H2). The gold electrode supplies the necessary electrons to replenish the InP nanocrystals.
In contrast to current processes, the new system works without organic molecules. These must be converted into an excited state to react, which causes them to degrade over time. This problem limits the lifetime of systems with organic components. The new system is purely inorganic and lasts correspondingly longer. “Our newly developed photocatalytic electrode system is robust, efficient, inexpensive, and free of toxic heavy metals,” according to Nann. “It may be a highly promising alternative for industrial hydrogen production.”
More information: Thomas Nann, Water Splitting by Visible Light: A Nanophotocathode for Hydrogen Production, Angewandte Chemie International Edition, http://dx.doi.org/ … ie.200906262
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Feb 09, 2010
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Also, solar cells are extremely inefficient, I think around 20%. If theirs is up to 60%, could we apply this to normal solar tehnology somehow? IMO efficienty is the major thing holding solar power back from being a major contributor.
Feb 09, 2010
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No, it actually produces hydrogen. A point that is sort of glossed over is that it does not produce oxygen. You need an electric current to balance this lack.
Of course, someone could come up with a better oxygen producer which completes the set. Then you can have hydrogen production here, and oxygen production over there, allowing the gasses to be collected separately. Or you could produce chlorine from salt water, or whatever you want on the other end.
Feb 09, 2010
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Feb 09, 2010
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Feb 09, 2010
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If this system really is 80% efficient, then the real news is that they have a super-efficient solar collection system.
However, I'm willing to bet that this is just more smoke and mirrors.
Feb 09, 2010
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You can change that ratio and remove just Hydrogen if you add electricity (and use appropriate catalysts). You're left with liquid water with a less than 2:1 ratio of H to O. Rather than the O ions joining to make gaseous O2, they stay in solution.
Feb 09, 2010
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Feb 09, 2010
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Feb 09, 2010
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probably happening is that the iron/sulfur complexes are cracking H2O to H+ and OH-. That is what the solar energy is doing.
The supplied current neutralizes that H+ ion before it recombines with the OH-, allowing the hydrogen to depart the area as a gas.
60 percent is fantastically efficient, for converting solar energy to fuel. The use of indium is a problem, however. At our current rate of use, and assuming 50% efficiency in recycling, we have about 10 years of indium left (minerals.usgs.gov/minerals/pubs/commodity/indium/indiumyb04.pdf).
At what rate and solar energy be captured, with 2500 metric tons of indium (the estimated world reserves)?
Feb 10, 2010
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