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 , 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 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 , the iron-sulfur complexes then pass their electrons on to hydrogen ions (H+) in the surrounding , 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 . 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.”

Explore further: Molecular assemblies created to convert water to hydrogen gas

More information: Thomas Nann, Water Splitting by Visible Light: A Nanophotocathode for Hydrogen Production, Angewandte Chemie International Edition, dx.doi.org/10.1002/anie.200906262

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danman5000
not rated yet Feb 09, 2010
So this doesn't actually split water, it just reduces hydrogen ions floating around? So then more acidic solutions should work better, right? I wonder how much acidity these cells would tolerate. Kind of a cool process - it generates gas magically without having to actually break any bonds.
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.
eachus
not rated yet Feb 09, 2010
So this doesn't actually split water, it just reduces hydrogen ions floating around?

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.
vivcollins
not rated yet Feb 09, 2010
Did I miss a step some were? I put in a bucket of water and I get hydrogen yes, but I am still left with the original bucket of water and not the bucket of oxygen I was expecting?
PPihkala
not rated yet Feb 09, 2010
I too have the same question: what happens to the oxygen that is part of water? It must go somewhere if hydrogen is extracted.
StillWind
1 / 5 (1) Feb 09, 2010
Yeah...I think someone missed out on a Chemistry class. You can't produce hydrogen from water without producing oxygen.
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.
Temple
5 / 5 (2) Feb 09, 2010
People did indeed miss some Chemistry. Liquid water is not a bunch of little Mickey Mouse ears of H20 molecules. It's a roiling mass of H and O ions whose concentrations (when pH neutral) is 2:1.

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.
baudrunner
5 / 5 (2) Feb 09, 2010
The process acts under the influence of an electric current, so hydrogen is more probably released. It does so efficiently in a bath of water cooperating with the electron current which attach themselves to the hydrogen ions in the water which do not happen to be already bonded to oxygen atoms, and in the presence of the catalyst. So oxygen is not a by-product which occurs in abundance. Hydrogen permeates everything. It's a wonder we haven't exploited its abundance under this premise before. Trouble is, everybody wants to play with building blocks.
baudrunner
not rated yet Feb 09, 2010
Great minds think alike. Sheesh!
retrosurf
1 / 5 (1) Feb 09, 2010
Since they mention a catalytic reaction, what is
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)?
tkjtkj
not rated yet Feb 10, 2010
" TEMPLE: People did indeed miss some Chemistry. Liquid water is not a bunch of little Mickey Mouse ears of H20 molecules."


OH-

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