Aug
19
On the Path To Renewable Hydrogen
August 19, 2009 | 8 Comments
Hydrogen is the key to cheap and abundant fuels. Carbon, plentiful and available in a wide array of forms is hardly in any short supply, but hydrogen seems to end up bound back with oxygen forming water. Breaking hydrogen back out, cheaply, is a goal of major importance.
A researcher team at the Dalian Institute of Chemical Physics at the Chinese Academy of Sciences has developed a new three-component photocatalyst that produces hydrogen with a quantum efficiency of up to 93% in the presence of sacrificial reagents powered by visible light irradiation, Its also very stable under the photocatalytic reaction conditions. This could be a major improvement that could be applied to fuel production.
Other synthetic light driven photocatalysts have achieved up to about 65% quantum efficiency. Natural photosynthetic systems can get to quantum efficiency of about 95%. These current efficiencies show the quantitative importance of the Chinese work.
Dalian Institute's Donge Wang sets up to measure light-stimulated catalytic hydrogen production from water.
The catalyst is cadmium sulfide doped with palladium sulfide and platinum (Pt–PdS/Cd) and achieves its extremely high quantum efficiency with loadings as low as 0.30 wt% of Pt and 0.13 wt% of PdS as co-catalysts on the CdS. More interesting is the catalyst does not split water into hydrogen and oxygen. Rather, it evolves hydrogen alone and does so only from aqueous solutions containing sulfur-based sacrificial reagents that consume oxygen. That’s serendipitous, as sulfur is in very abundant supply. What expenses come in from deoxidizing the sulfur isn’t yet being considered.
The story goes that while searching for the composition that yields the most active photocatalyst, authors Li, Hongjian Yan, Jinhui Yang, and coworkers (Journal of Catalysts, doi:10.1016/j.jcat.2009.06.024) observed that pure CdS evolves hydrogen from water very slowly. The team found that doping CdS with platinum or palladium greatly increases the hydrogen yield. However they found doping CdS with both metals offers little additional benefit. So the team took another approach: They doped CdS with PdS, which boosted CdS’s activity by more than a factor of 260. Then they co-doped CdS with PdS and platinum and found the three-component material to be 380 times more active than pure CdS. There seems to be no inherent limit to the creatively available in catalysts.
Sunlight Hydrogen Catalyst. Click image for more info.
The explanation proposed is that PdS serves as an oxidation cocatalyst (co-dopant), and platinum’s role is to facilitate reduction. Li notes that further work is already under way to firmly establish the roles of each of the components.
First on the observer quotes is Kazunari Domen a photocatalysis expert at the University of Tokyo. He says, “The reported quantum efficiency of hydrogen evolution is remarkably high.” In a report at Chemical & Engineering News Domen adds that the requirement for sacrificial sulfur compounds might be exploited, for example, to produce hydrogen from sulfur-laden petroleum products. Considering the hills being built of sulfur at the Canadian Syncrude facility the idea seems practical. But in Domen’s view, the most significant aspect of the work is the novel combination of cocatalysts, which will likely motivate other researchers to explore that strategy in the search for better performing catalysts.
Chemical & Engineering news has a page about the research with two videos showing activity driven by powered visible light and in full sunlight. It seems that the catalyst works across a large share of the visible spectrum. Development might be to completely cover the available spectrum to find a cost basis for commercialization.
Keep in mind; this isn’t a “breaking the bond” process, its very intuitive chemistry yielding the desired result. That suggests achieving a full 100% quantum efficiency might be possible and may not be an upper limit. The waste would be a sulfur oxide, which may be a product with usefulness in commercial volumes.
The research greatly advances the decades-old search for an inexpensive way to produce hydrogen using water as the resource. The prospects for more and cheaper hydrogen can be a little mind boggling when the opportunities are considered making the Chinese research much more important than news editors might think. There might be some thought given to what form of sunlight processing is most profitable in a range now from thermal solar, photovoltaic and likely soon – hydrogen production.
Solar energy is getting much more interesting. The new catalyst is amazing in efficiency, but how productive is it?
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http://www.newscientist.com/article/dn17632-how-to-turn-seawater-into-jet-fuel.html
Here is a link about a US Navy attempt to extract CO2 from sea water where it is 140 times more concetrated than in the atmosphere. Combine it with hydrogen in the Fisher-Tropsch process and viola – Jet Fuel.
About f**king time. the seven sisters have been
screwing us more than long enough. I’d really
like to put all the big shots under chemical
interrogation.
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