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New Photoelectrocatalytic Method for the Solar Production of Hydrogen from Water

A team led by Thomas Nann and Christopher J. Pickett at the University of East Anglia (Norwich, UK) has introduced an efficient, robust photoelectrode made of common, inexpensive materials for the production of hydrogen by splitting water with sunlight. A paper on their work was published online 5 February in the journal Angewandte Chemie.

Nann
UEA researchers developed a novel nanophotocathode for hydrogen production that is based on a multilayer array of InP quantum dots activated with a synthetic diiron catalyst, which is related to the subsite of FeFe hydrogenase. Credit: Wiley-VCH. Click to enlarge.

The new system consists of a gold electrode that is covered with layers of indium phosphide (InP) nanoparticles. The researchers then introduced 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%.

The UEA 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.

“This relatively high efficiency is a breakthrough.”
—Thomas Nann

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. It may be a highly promising alternative for industrial hydrogen production.

—Thomas Nann

Resources

  • Thomas Nann et al. (2010) Water Splitting by Visible Light: A Nanophotocathode for Hydrogen Production. Angewandte Chemie International Edition doi: 10.1002/anie.200906262

Comments

kelly

“This relatively high efficiency is a breakthrough.”
—Thomas Nann

sulleny

Technology transfer bailout for corruption riddled UEA.

Eletruk

So is the 60% efficiency based on the electricity used? Or is it based on the total energy input (including solar)?
And what happens to the Oxygen from the reaction? Is this in reality the "degradation" of the organic components. So now we also need to take into account the energy used to created the components, because that energy is actually part of the whole equation.
So overall efficiency may not really be that great.

Tim Duncan

Eletruk,
Do you mean they should consider the energy to build the catalyst as part of the basic efficiency? I doubt this makes sense if their cat durability claim is true.
I would like to know more about their equation to come to the 60% though? Is that considering just the energy of the hydrogen or counting the oxygen also? If later, how does one count the lower heating value of oxygen? Does anyone have any insights on this calculation?

jfinlayson

Says "inexpensive material", but gold and platinum (not mentioned here, but in the New Scientist article describing the same work) are hardly inexpensive.

jfinlayson

And indium, while less expensive than gold and platinum, might have difficulty scaling. World reserves stand at 6,000 tons (a mere 13 year supply at this rate). It's been an issue hanging over the head of the CIGS development community. Not an issue while it's still in the lab, but if we're serious about making PV a big part of our future energy supply, there won't be enough indium.

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