Although they know it’s going to be a long ride until some successful commercial release, scientists tinker with artificial photosynthesis, speculate new ideas and come up with newer experiments, meant to eliminate the middlemen-processes in the direct solar hydrogen production.
This time a team of researchers from the MIT, led by Professor Angela Belcher, used a modified virus as a biological scaffold for assembling the nanoscale components needed to split water into hydrogen and oxygen. The bacterial virus is called “M13”, and it’s said to be harmless.
They used the M13 to attract and bind the molecules of a catalyst (iridium oxide) and a biological pigment (zinc porphyrins), making the viruses become wire-like structures that could split water very efficiently and get the oxygen out.
Eventually, because the virus-wires clumped together and lost their effectiveness, the researchers encapsulated them in a microgel matrix, maintaining their uniform arrangement, stability and efficiency.
Besides getting the oxygen out of the water, there is the problem of hydrogen, which is in fact the main issue. Plants and cyanobacteria have highly organized photosynthetic systems for the efficient splitting of water, so Belcher’s team tried to mimic their working behavior, rather than directly importing matter from live bacteria, for prolonging the system’s life.
Acting like some kind of a scaffolding, the lined-up viruses caused the pigments and catalysts also to line up, with the right kind of spacing between them to allow sunlight start the water splitting reaction.
The role of the pigments is “to act as an antenna to capture the light,” Belcher explains, “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.
“We use components people have used before,” she adds, “but we use biology to organize them for us, so you get better efficiency.”
Using the virus to make the system assemble itself improves the efficiency of the oxygen production fourfold, Nam says. The researchers hope to find a similar biologically based system to perform the other half of the process, the production of hydrogen. 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 more commonplace, less-expensive material for the catalyst, to replace the relatively rare and costly iridium used in this proof-of-concept study. To be cost-competitive with other solar solutions, the system devised by them has to be at least 10 times more efficient than natural photosynthesis, to be able to run for years, and use cheaper materials.
Although we shouldn’t expect this artificial photosynthetic system to go commercial anytime soon, prof. Belcher is optimistic and says in two years time they’ll have a fully working prototype that should be able to satisfy all the market requirements stated above.