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FOR years, polystyrene foam has been keeping our coffee hot and our beer
cold. Now chemists have taught single molecules of this plastic a more
impressive trick—how to snatch and store energy from light in the way that
plants do.

The researchers, based as the Los Alamos National Laboratory in New Mexico,
are aiming to build a new breed of cheap polystyrene-based batteries. They say
the batteries could be used to provide power for anything from cars to
cellphones.

The project is part of continuing efforts by Tom Meyer and his colleagues at
Los Alamos to find simple materials that can mimic the complex chemistry of
photosynthesis, which allows plants to store energy from sunlight in chemical
bonds.

The first step in photosynthesis is the absorption of a photon—a
particle of light—by an “antenna” composed of the green pigment
chlorophyll. This energy is then used to propel electrons around the chemical
bonds of the molecules involved in the reaction, ultimately stripping electrons
from water to make oxygen, and adding them to carbon dioxide to create
energy-rich sugars.

Meyer’s team had already managed to recreate each of these steps separately,
using different synthetic molecules that work in conjunction with an atom of the
metal ruthenium. In his latest experiments, he decided to link these molecules
on a polymer backbone. “Because polystyrene polymers are so widely used, their
chemistry is very well understood,” he says. “So it was an obvious choice for
the backbone.”

To test out the new molecule, the researchers zapped a solution of it with a
laser. As they had hoped, some side chains containing the ruthenium antennas
were able to absorb the light energy and pass it along the polymer chain. When
the energy reached another type of ruthenium complex, it was able to do some
chemical work, pushing an electron to a different part of the complex.
Mobilising electrons in this way is what batteries do—supplying electrons
from an anode that can be drawn around a circuit and back towards its
cathode.

Michael Wasielewski, a photosynthetic chemist at Northwestern University in
Chicago, thinks Meyer’s choice of polymer was the key. “All the right properties
are there,” he says. “And we already have robust [manufacturing] technology to
work with polystyrene. It’s a nice piece of work.”

Because polystyrene derivatives are inexpensive to create, Meyer thinks his
polymer holds great promise for a wide array of devices—such as
solar-powered fuel cells that pull electrons from water to create hydrogen fuel
or to generate an electric current.

For now, his team’s main aim is to increase the efficiency with which the
molecules convert energy, which is now hovering around 15 per cent. “There’s a
lot of hard work ahead, but you have to expect that,” he says. “After all, it
took natural photosynthesis more than a billion years to evolve.”