Nature is amazing. Take the humble leaf—it’s capable of absorbing the sunlight and converting it into the chemical energy that fuels the growth of plants. Photosynthesis is one of the fundamental forces of life, and it’s far superior to our technological efforts to harness sunlight. A photovoltaic solar panel can transform sunlight to electricity, but right now that power is difficult to store without expensive batteries, which limits the potential of solar energy. The sugars produced by photosynthesis, though, can be tapped by a plant for energy whenever it’s needed. A solar cell that could mimic photosynthesis would be a game changer for alternative energy.
As it turns out, we may be getting close. In an article published in the September 29 Science, Massachusetts Institute of Technology (MIT) professor Daniel Nocera and his colleagues announced the development of an effective, relatively inexpensive “artificial leaf”—a solar cell that can turn sunlight directly into chemical fuel. The playing card-sized device is made up of cheap materials—silicon, cobalt and nickel mostly—and when placed in a container of water and exposed to sunlight, it generates bubbles of oxygen and hydrogen. Those gases can be collected and stored—much more easily than the electricity produced by a photovoltaic solar cell—and then used to generate power through a fuel cell.
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As Nocera explained to the Financial Times, his device directly mimics nature:
It’s doing exactly the same thing as a leaf. It’s sunlight in; hydrogen and oxygen out. And you can use the hydrogen and oxygen at some later time.
Nocera has been working on the artificial leaf for some time—he’s called it the “Holy Grail” of renewable electricity. (We put Nocera on our TIME 100 list in 2009 for his work on artificial photosynthesis.) He believes the invention could make solar power affordable and viable for poor, off-the-grid locations—which is one reason why the Indian conglomerate Tata has helped finance his research. That’s why the artificial leaf is so simple—no excess equipment, no expensive materials. Ideally, the cell could produce enough electricity to power a house in a developing country with just sunlight and a gallon of water.
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To keep his cells cheap, however, Nocera needs to sacrifice some efficiency—how much sunlight his cell can convert into energy. The standard commercial solar PV cell has an efficiency rate of about 10%—the artificial leaf right now is closer to 2.5%. That’s still significantly more efficient than the average actual leaf, but of course, human beings need a little more power than trees. The artificial leaf also has to be durable enough to last for thousands and thousands of hours—an older prototype, developed more than a decade ago by John Turner of the U.S. National Renewable Energy Laboratory lasted barely a day. Nocera’s leaf has operated continuously for at least 45 hours, according to earlier presentations, but it will need to do better.
Still, at a moment when most of the attention on renewable energy is being directed towards phony “scandals,” it’s a good to see what a smart and dedicated scientist can do to change the way we power our lives.
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