An MIT team has managed what amounts to artificial photosynthesis, using a modified virus and sunlight to split water into hydrogen and oxygen atoms.
The hydrogen can then be stored and used to generate electricity using a fuel cell, or to make liquid fuels for cars and trucks.
It's the first time sunlight has been used to power such a reaction directly.
The team engineered a bacterial virus called M13 so that it would attract and bind with molecules of a catalyst - the team used iridium oxide - and a biological pigment, zinc porphyrins. The viruses became wire-like devices that could very efficiently split the oxygen from water molecules.
To prevent the virus-wires from clumping together and losing their effectiveness, the researchers encapsulated them in a microgel matrix, so they maintained their uniform arrangement and kept their stability and efficiency.
While hydrogen's the useful stuff, it's the splitting of oxygen from water that's most difficult, so this is where the team focused its efforts.
Other researchers have tried to use the photosynthetic parts of plants directly for harnessing sunlight, but these materials can have structural stability issues.
In the team's system, the viruses simply act as a kind of scaffolding, causing the pigments and catalysts to line up with the right kind of spacing to trigger the water-splitting reaction.
The role of the pigments is "to act as an antenna to capture the light," explains Angela Belcher, the Germeshausen Professor of Materials Science and Engineering and Biological Engineering, "and then transfer the energy down the length of the virus, like a wire. The virus is a very efficient harvester of light, with these porphyrins attached."
Currently, the hydrogen atoms from the water get split into their component protons and electrons; a second part of the system, now being developed, would combine these back into hydrogen atoms and molecules. The team is also working to find a less-expensive material for the catalyst.
Thomas Mallouk, the DuPont Professor of Materials Chemistry and Physics at Pennsylvania State University, who wasn't involved in the research, says, "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."
To be cost-competitive with other approaches to solar power, he says, the system would need to be at least ten times more efficient than natural photosynthesis, be repeatable 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."
The research is described in Nature Nanotechnology.