Researchers have combined the photosynthetic power of spinach with silicon to produce an electrical current that could one day be harnessed to produce fuel, charge a battery or run a solar array on a small electrical device. Call it Popeye Power.
The combination of a protein called Photosystem 1 (PS1) and the silicon produces current levels almost 1,000 times higher than putting the protein on various kinds of metals, according to David Cliffel, associate professor of chemistry at Vanderbilt University who published the paper this week in the journal Advanced Materials. Kane Jennings, professor of chemical and biomolecular engineering at Vanderbilt and a collaborator on the project, said he hopes to produce a working prototype within three years.
PS1 is the protein that converts sunlight into electrical energy in plants. Cliffel said he chose the spinach leaf because the stems are big and easy to remove, making it a perfect lab model.
"It's dark green so you’re guaranteed of getting a fair bit of protein,” Cliffel said. “We were using the farmers’ market stuff, but then just waited until delivery day at Kroger’s.”
Scientists are hoping to use similar “bio-hybrid” cells to generate energy because of their great efficiencies and because they are cheaper than using exotic metals like titanium or iridium, for example.
“One of the benefits of this is that you could build a photocell that stands up to charging up your batteries, or generates a fuel,” Clifell said. He imagines that such a cell would be able to power small devices in remote areas far from the electrical grid.
While the spinach-silicon device would probably work to store solar energy, it would have a hard time outperforming existing photovoltaic cells, according to Jon Golbeck, professor of biochemistry at Penn State University.
“All these hybrid technologies will have to compete with solar cells, which work for 20 years but are still expensive,” Golbeck said. “But creating fuel is the gold at the end of the rainbow. He has much better chance of succeeding there.”
Golbeck said the state of the art in creating biohybrid cells is still relatively new and that federal funding has only come in recent years. “Nobody knows where the breakthroughs are going to be,” he said. “There has to be hundreds of failures to get one to work.”
Cliffel said he’s been working on an experiment to produce photosynthetic hydrogen through the same process, hydrogen that could be used as a fuel.
In the current paper, the Vanderbilt researchers report that their PS1/silicon combination produces nearly a milliamp (850 microamps) of current per square centimeter at 0.3 volts. That is nearly two and a half times more current than the best level reported previously from a biohybrid cell.
Clifell and his colleagues extracted PS1 from spinach into an aqueous solution and poured the mixture on the surface of a silicon wafer. Then they evaporated the water in a vacuum chamber leaving a film of protein.
Clifell says he’s working with other leafy green plants as well, including the infamous invasive southern vine, kudzu.
Photo credit: Vanderbilt University