Sunday, September 5, 2010

How to replicate photosynthesis in the lab?

Though we like to say for ourselves that we are technologically and scientifically very advanced there are still some "simple" processes that scientists cannot successfully copy in their laboratories, and one of these processes is photosynthesis, as scientists are still not able to copy plants in their process of converting sunlight into stored energy, and doing this process reliably day after day, year after year. If scientists would be able to copy this process this would turn solar energy into one of the most efficient energy sources in the world, making it competitive to fossil fuels, and this would in the end resulted in less harmful CO2 emissions responsible for climate change.

However, the road from "if" to "yes" is very long, and scientists, despite their constant research still struggle to be as effective as plants are. One of the main stumbling blocks on the road is the fact that the sun's rays can be highly destructive to many materials, which can lead to the degradation of harvesting systems, which can significantly decrease efficiency of the process on the long run. Plants are able to bypass this issue by constantly breaking down their light-capturing molecules and then reassembling them from scratch, so the basic structures that capture the sun's energy are always brand new.

Can science also bypass this issue? If the latest reports are correct, then yes it can, though still not as effective as plants can. In fact some MIT scientists have recently created a novel set of self-assembling molecules that can turn sunlight into electricity. These molecules can be repeatedly broken down and then reassembled quickly, just by adding or removing an additional solution.

Specifically for this process scientists produced synthetic molecules called "phospholipids" that form discs, and these discs provide structural support for other molecules that actually respond to light, in structures called reaction centers, which release electrons when struck by particles of light. The discs, carrying the reaction centers, are in a solution where they attach themselves spontaneously to carbon nanotubes. The nanotubes hold the phospholipid discs in a uniform alignment so that the reaction centers can all be exposed to sunlight at once, and they also act as wires to collect and channel the flow of electrons knocked loose by the reactive molecules.

The final results showed efficiency of these new molecular structures in converting sunlight at about 40 percent, which is double the efficiency of today's best commercial solar cells. Theoretically, the efficiency of the structures could be close to 100 percent. The efficiency would be far better if it wasn't for the fact that the concentration of the structures in the solution was low, so the overall efficiency of the device, and thus the amount of electricity produced for a given surface area was fairly low. But scientists are already working on ways to significantly increase the concentration, and thus improve the efficiency of the process.