When visitors come to Pamela Silver’s Harvard lab, they always ask to see the “bionic leaf.”
“And they’re going to be disappointed,” the biochemist said, laughing heartily. The experiment that has kept Silver and her colleagues occupied for the better part of the past year is little more than a humble jar. Several inches of cloudy, bacteria-filled liquid sits at the bottom, and a tangle of wires protrudes from all sides.
“It really looks nothing like a leaf,” Silver said. It’s even better.
On Thursday, Silver and her colleagues report in the journal Science that they’ve combined solar panels, genetically modified bacteria and a synthetic catalyst to create a system that does exactly what a leaf does – turn sunshine into fuel – but much more efficiently.
“Photosynthesis really is unbelievable,” said Silver’s colleague Daniel Nocera, a fellow Harvard professor and a co-author of the report. “It’s just water, air and sunlight, and plants can make biomass from that. And we can, too.”
If it’s been a while since your high school biology class, here’s a photosynthesis refresher: Plants take in water and carbon dioxide. Using sunlight as their energy source, they split those molecules into their component parts and reshape them as water, oxygen and, most important, complex sugar. Almost all the energy used on Earth traces back to those vital sugar molecules.
For years now, scientists have been working with a bacterium, Ralstonia eutropha, that can perform the tail end of this process – turning assorted carbon, oxygen and hydrogen atoms into energy. But providing Ralstonia with the ingredients it needs for this process has proved complicated. Too often, the catalysts used to launch the reaction that splits water and carbon dioxide molecules would also produce toxic byproducts – killing the bacteria before they could do their jobs.
So Nocera, who specializes in renewable energy, started to develop a new one. The catalyst he ended up with, made of cobalt and phosphorus, jump-starts the water-splitting reaction without poisoning the rest of the system.
The end product is about 10 times better at turning sunlight into biomass than even the fastest-growing plants, Nocera says. The system can also produce a host of useful compounds: biofuels such as isobutanol, for example, or the molecule PHB, which can be used to make biodegradable plastic. Once it’s scaled out of the lab – and ditches the dinky jar apparatus – the system could conceivably produce renewable energy for all manner of uses.
Inspired by a clause in last year’s Paris climate agreement that called for more research on alternative energy to take place in developing countries, Nocera is planning to share his research with colleagues in India.
“It’s like a giving pledge,” he said, referring to the agreements some of the world’s richest people sign committing to donate a certain portion of their wealth. “I don’t have billions of dollars, but I can give my discoveries … to Indian scientists and engineers and they can scale it themselves,” putting the technology to use in the countries that need it most.
Will it work? Nocera has roped his economist colleagues at Harvard and the University of Chicago into the initiative. But he’s still not certain.
“This is also an experiment,” he said.