Using artificial photosynthesis (in a virus) to split water

In general, SciTechStory doesn’t start tracking a technology that’s (a) incomplete in implementation and (b) many years from application (if ever). Maybe this one is an exception: Using a virus to support artificial photosynthesis that splits water into oxygen and hydrogen. It sounds pretty strange (not that this is a qualification for coverage herein), but it’s also indicative of the kind of creative research that’s occurring around artificial photosynthesis. (The discovery of Nature using quantum effects for photosynthesis is another such interesting track.)

The development of a ‘natural’ (biological) and efficient way to split water is potentially very important. Of course, there are many uses for deriving hydrogen from water – fuel cells, hydrogen cars, for example. This particular approach, developed by a team led by Angela Belcher (Massachusetts Institute of Technology, USA), professor of materials science, uses a common bacterial virus (a virus that infects only bacteria) as the structure (or scaffolding) to hold the photosynthetic components. The virus was genetically engineered to bind to the two components: zinc porfyrins, a kind of organic pigment (like the red in red blood cells), which was used as the photoreceptor; and iridium oxide, which was the catalyst for the conversion.

The treated viruses became, in effect, wires. They became wires that absorb photons from light for energy and hold the catalyst for the chemical reaction with water. Most other approaches to photosynthesis have tried to use the organic (plant) material, usually resulting in dead plant material. Dr. Belcher reasoned that it might work better to use the organic matter as a scaffold to hold the artificial components in place. Better still, the virus proves to be an active organizer of the photosynthetic process, making it more efficient.

There is a problem though, right now the photosynthetic process produces oxygen and also splits the hydrogen into its fundamental protons and electrons. Now the researchers have to come up with a way to put the protons and electrons back together as hydrogen. This is what I meant by a technology not fully implemented. They’re also trying to find a catalyst that is less expensive than iridium oxide. The prognosis might be even gloomier. Take the words of Thomas Mallouk, the DuPont Professor of Materials Chemistry and Physics at Pennsylvania State University, who was not involved in this work…

“This is an extremely clever piece of work that addresses one of the most difficult problems in artificial photosynthesis, namely, the nanoscale organization of the components in order to control electron transfer rates.”

He adds: “There is a daunting combination of problems to be solved before this or any other artificial photosynthetic system could actually be useful for energy conversion.” To be cost-competitive with other approaches to solar power, he says, the system would need to be at least 10 times more efficient than natural photosynthesis, be able to repeat the reaction a billion times, and use less expensive materials. “This is unlikely to happen in the near future,” he says. “Nevertheless, the design idea illustrated in this paper could ultimately help with an important piece of the puzzle.”

[Source: EurekAlert]

I was particularly struck by the phrase “…need to be at least 10 times more efficient than natural photosynthesis…,” which will be difficult because photosynthesis is about 3-6% efficient. Hitting 60% efficiency will be…difficult; 30% perhaps not so much. In any case, the researchers are aware that this is just the beginning of the road to artificial photosynthesis and/or conversion of water to oxygen and hydrogen by natural means. Whatever the ultimate practical value, the point is still made: This kind of work opens eyes, provides new methods, and perhaps will provide insights that are useful for other, better, approaches.

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  1. Posted March 8, 2013 at 1:24 am | Permalink

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