On a sunny day on the campus of the University of California, Berkeley, the peaceful rustling of eucalyptus trees belies the furious chemical activity happening inside every single leaf. Through photosynthesis, leaves use the energy in sunlight to turn water and carbon dioxide into substances that plants need, emitting only oxygen in the process. In a nearby lab, chemist Peidong Yang is building an artificial system that does the same, using arrays of nanowires coupled with engineered bacteria. If something like this is ever scaled up, it would churn out a better version of the fuels we use today—one that does not add to the total amount of carbon dioxide in the air.

Photosynthesis has been very difficult to imitate in the lab. In the 1970s, researchers at the University of Tokyo showed for the first time that a solar-powered device could do what plants do in the first step of photosynthesis: split water into hydrogen and oxygen. After an initial burst of activity, the field stalled. But it has been reborn in several labs thanks to a renewed focus on the energy problem and climate change—and because of the emergence of new technologies.

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