Supplying the World's Energy Needs with Light and Water

A leading chemist says that a better understanding of photosynthesis could lead to cheap ways to store solar energy as chemical fuel.
While researchers and technologists around the world scramble to find cleaner sources of energy, some chemists are turning to nature's own elegant solution: photosynthesis. In photosynthesis, green plants use the energy in sunlight to break down water and carbon dioxide. By manipulating electrons and hydrogen, oxygen, and carbon atoms in a series of complex chemical reactions, the process ultimately produces the cellulose and lignin that form the structure of the plant, as well as stored energy in the form of sugar. Understanding how this process works, thinks Daniel Nocera, professor of chemistry at MIT, could lead to ways to produce and store solar energy in forms that are practical for powering cars and providing electricity even when the sun isn't shining.

What's needed are breakthroughs in our understanding of the fundamental chemical processes that make photosynthesis possible, according to Nocera, a recognized photosynthesis expert. He is studying the principles behind photosynthesis and applying what he learns to making catalysts that use solar energy to create hydrogen gas for fuel cells. Nocera's goal: a world powered by light and water.

Technology Review: What's the biggest challenge related to energy right now?

Daniel Nocera: The real challenge with energy is the scaling problem. We're going to have this huge energy need, and when you start looking at all the numbers, there's only one supply that has scale, and it's the sun. But it's still a research problem. Technologies all follow lines; then there's a discovery and a new line that's better. We're on a very predictable line now in solar. Most things you hear about are incremental advances.

TR: You're studying photosynthesis to get ideas for how to convert sunlight into a chemical fuel--hydrogen--for use when the sun isn't shining or in powering fuel-cell vehicles.

DN: You can use the electricity directly when the sun is out, in places that have sun. [But] you need storage. There's absolutely no way around it. I am distilling the essence of photosynthesis down to be able to use it.

TR: Why is photosynthesis attractive in finding a source of clean energy?

DN: [Photosynthesis] does three things. It captures sunlight, and [second,] it converts it into a wireless current--leaves are buzzing with electricity. And third, it does storage. It stores the converted light energy in chemical energy. And it uses that chemical energy for its life process, and then it stores a little.

It turns out [that] photosynthesis is one of the most efficient machines in the world for energy conversion. But it's not great for storing energy because that's not what [a plant] was built to do. It was built to live and grow and reproduce.

And so that's the approach we take. Can we now do what the leaf is doing artificially, which is the capture, conversion, and storage in chemical bonds? But my device doesn't have to live: it can take a lot more of that energy and put it into chemical bonds.