Quantum efficiency is not the same as energy efficiency. Quantum efficiency refers to the fraction of photons that lead to the desired reaction, rather than the fraction of the photons' energy that is used rather than dissipated as heat.

I'm a little confused about the term "photooxidation". Normally, taking oxygen out of a compound is considered a chemical reduction. How is splitting H20 to yield H2 and O2 an oxidation process?

I'm a little confused about the term "photooxidation".

Oxidation in general means 'removing electrons from'. Here, the photogenerated holes remove electrons from water. I guess the reaction is something like:

H2O --> 1/2 O2 + 2 H* + 2e-

or

2 OH- --> 1/2 O2 + H2O + 2e-

i can't help but agree that the given spec does appear to mean 27 W/m^2.

of course, that is from an early experimental setup so may not represent the technologies real efficiency.

most importantly, though, is the expected system cost, which could be significantly lower than Si-based tech, since the most expensive material listed is iron.

Energy geek observations:

"Deposition of silicon-doped nanocrystalline hematite films by APCVD produces Fe2O3 photoanodes that oxidize water under visible light with unprecedented efficiency. The dendritic nanostructure minimizes the distance photogenerated holes have to diffuse to the Fe2O3/electrolyte interface in a film that is thick enough for strong light absorption."

Most interesting is the process' dendritic nanostructure mimicking more commonly recognized neurological biology. And the layered process allowing wide spectrum absorption.

Assuming the cost of sunlight at near zero - a hematite semiconductor producing H2 @ +20% efficiency might be a business - if scaled manufacture costs are reasonable and H2 capture and storage have no significant problems.

To clarify the "oxidation" discussion, Paul Dietz is correct that the use of the term is in reference to the loss of electrons by the oxygen atoms, and everyone is correct to point out that it's not the most accurate description.
In terms of formal oxidation states, the oxygen in water is at oxidation state -2, while the hydrogen atoms are at +1. After the reaction, which is balanced as:

2 H2O --> 2 H2 + 1 O2

the hydrogen atoms in H2 and the oxygen atoms in O2 are all at oxidation state 0, so the oxygen atoms have been oxidized (from -2 to 0), and the hydrogen atoms have been reduced (from +1 to 0).

This reaction is more accurately called a disproportionation since the electron donor and acceptor are within the same molecule, but "oxidation of water" seems to have caught on as a general term for this reaction.

In response to Baldwin, who called this project daft - I must disagree.

For one, the research into this sort of cell has much scientific overlap with the design of solar -> electron conversion cells -- as it does electron -> light (LED) circuits. Gratzel is known for the Gratzel cell - a solar -> electron device. Photon -> hydrogen are his new hobby.

Secondly... hydrogen might very well come in handy to power long distance big rig trucks, long distance cargo ships, and possibly jets. Basically, anything that would be impractical to power via batteries. It may not be hydrogen that powers these -- it may be methanol. You can make methanol by reacting with ambient CO2 (read about the methanol economy)

Lastly.. This man is a genius -- I think we can trust he'll choose what is best to work on.

Take care --
Matt

John,

Roger made a good suggestion in another post re: H2 fired power plants, derived from on site bioreactor farms. Such a scheme would surely require buffering if not outright storage of H2 prior to combustion. Granted it's not an immediate broad-based energy solution for transportation - but there will be vertical applications for H2 in the energy future.

www.greencarcongress.com/2006/12/arizona_public_.html

Now how about working on the plutonium to store it?
Then there is the problem that you can't park it anywhere just like Natural Gas cars are prohibited.
Would you want to keep a hydrogen bomb in your air-tight garage? Only 1/10th of the energy required for gas to explode will ignite hydrogen. No more cellphones in cars - too dangerous. Static from rubbing your hands on your car seat when there is a microscopic leak in the hydrogen tank - explosion. Focus on non-flammable batteries like Saphion or nanosafe. Or improve biodiesel , svo , wvo engines. Moms want safety not just innovation.

Garden variety means convert it to something normal people understand, like Dollars, or production.

Does this finding revolutionize the production of Hydrogen or just get closer to being marginally sub-standard to gasoline.

Will the people that sell Hydrogn switch from conversion of natural gas as feed stock to water because of this?

"We" aren't wasting our time. At the very worst, Gratzel and his associates are wasting their time; which is entirely their right. (Although I doubt that this example is a waste of time, this is useful basic science.)

The more important thing is that Gratzel et al. created a production process for making materials that can be used for other photoelectrochemical processes. This will turn out to be a very useful engineered material.

Also, H2 is needed in a lot of chemical processes where this technology can be fully controlled. I can think of two derivative uses for the technology in the making of methane with CO2 (instead of using natural gas or petroleum oils) which can then be used for monomers and plastic production; and in the use of H2 in fuel cells for residences (again, instead of natural gas).

Both examples of industry and residences are huge producers of GHGs. I think it is silly to require broad-spectrum GHG reductions across the board right out of the gate. Maybe a first good step is offsetting GHG production in chemical production and home use while engineers work on the personal vehicle sources of GHGs.

True, H2 use in vehicles is a tricky engineering problem (as compared to a basic research problem), but I have faith that smart, well-motivated people will prevail over the minor engineering issues that remain to make the technology economic in a "user with an 80 IQ" world.

Now how about working on the plutonium to store it?
Then there is the problem that you can't park it anywhere just like Natural Gas cars are prohibited.
Would you want to keep a hydrogen bomb in your air-tight garage? Only 1/10th of the energy required for gas to explode will ignite hydrogen. No more cellphones in cars - too dangerous. Static from rubbing your hands on your car seat when there is a microscopic leak in the hydrogen tank - explosion. Focus on non-flammable batteries like Saphion or nanosafe. Or improve biodiesel , svo , wvo engines. Moms want safety not just innovation.

Sigh. The error density of this post is really impressive. Hydrogen's lower explosive limit is 4.0%. Gasoline is 1.2%. Hydrogen is light, so it disperses upward in air. Hydrocarbons creep along the ground untile they find an ignition source. Plutonium to store it? Huh? Hydrogen is stupid, but it isn't particularly dangerous. On the other hand, maybe we could exploit fear and ignorance to get the public to put a stop to the hydrogen nonsense. Sort of like the Bush administration, only for good instead of evil.