Nanoscale Control of Energy Flow

A few billion years ago, cyanobacteria, sporting the first chlorophyll molecules, performed an amazing feat; they captured the energy in sunlight and stored it in the chemical bonds of newly forged molecules.

Nature’s had a long time to refine and customize this energy-conversion act, and we humans marvel at its efficiency. If we could use the sun’s rays as effectively, we could address many of the world’s energy concerns. But right now, even our most impressive commercial solar panels capture less than 25% of sunlight’s energy.

Nature has given us these systems for free. We just need to figure out how to best use them.
UCB chemistry professor Birgitta Whaley

Researchers at ENSI are working to emulate nature’s photosynthetic adeptness. Some are inventing new nanostructures to aid in the process. Others, such as Profs. Birgitta Whaley and Graham Fleming, aim to better understand and make use of—and expand on—the light-capturing process itself.

In low light, plants are able to use about 90% of the photons they absorb to initiate photosynthesis. They sacrifice some of this efficiency, though, when the light is stronger, because all those photons keep the chlorophyll busy. The plant ends up dumping valuable light energy as heat.

This process works fine for serving the needs of a plant, Whaley points out, but not of a human society. So, while chlorophyll and photosynthesis can be quite efficient, the system as a whole can be improved upon.

Whaley’s long-term vision involves leveraging the variety of ways in which different organisms photosynthesize. For example, some bacteria survive by tapping into heat—infrared radiation—from deep sea vents. Whaley points out that joining the plant and the bacterial systems would expand the energy-gathering range beyond visible light. “If we’re designing artificial systems,” she says, “there’s no reason why we shouldn’t increase the bandwidth.

There’s also no reason not to combine the exquisite front end of photosynthesis with a back end tailored to a specific energy need. “We don’t want to mess with the part that absorbs light,” Whaley says. “We want to take that and use it to make a hybrid device.” She imagines taking nature’s light-gathering machinery and embedding it in a membrane that includes nanoscale structures designed to produce only a specific, desired energy-rich substance.

UC Berkeley chemistry professor and MacArthur fellow Peidong Yang is leveraging nature in a different way. He’s created a structure that can capture the energy in light and then transfers that energy to bacteria, which forge the bonds of energy rich-molecules. But rather than the glucose that plants and bacteria produce, Yang’s system makes hydrocarbons such as acetate or methane, the primary component of natural gas. And just like natural photosynthesis, Yang’s system uses carbon dioxide to obtain the carbon and oxygen atoms that become incorporated in more complex organic molecules.

Chemistry professor Birgitta Whaley

Chemistry professor Peidong Yang