Plants are amazing little powerhouses, converting sunlight, water and carbon dioxide into energy. Over the last few years humans have tried to mimic this with artificial leaves, but they're never quite up to scratch. Now, researchers from the University of Illinois at Chicago have designed a new version that could work under real-world conditions, sucking carbon dioxide out of the air and creating oxygen and synthetic fuels.
One of the first artificial leaves came out of Harvard in 2011, using sunlight to split water into harvestable hydrogen and oxygen gas. Other versions since then have used similar technologies to create electricity, liquid fuels, fertilizer, and even drugs. Currently, the most promising artificial leaves do a decent job of absorbing carbon dioxide, but only under lab conditions.
"So far, all designs for artificial leaves that have been tested in the lab use carbon dioxide from pressurized tanks," says Meenesh Singh, corresponding author of the study. "In order to implement successfully in the real world, these devices need to be able to draw carbon dioxide from much more dilute sources, such as air and flue gas, which is the gas given off by coal-burning power plants."
The UIC researchers say their new artificial leaf design is that kind of real-world ready. And it sounds surprisingly simple – it's basically a regular old artificial photosynthesis unit, wrapped in a new transparent capsule. This outer layer is a semi-permeable membrane made of quaternary ammonium resin, and it's filled with water.
The idea is that when the sun hits the device, the water slowly evaporates out through those pores. In its place, carbon dioxide is selectively sucked in from outside. In turn, that gas is converted into carbon monoxide by the artificial photosynthesis unit on the inside. From there, the carbon monoxide can be captured and used for a range of purposes, such as making synthetic fuels. Oxygen is a by-product as well, which can also be collected or just released back into the outside air, like a natural plant would do.
The researchers say their design would be up to 10 times more efficient at this process than a natural leaf. If enough of them are gathered in one place, that could produce a decent amount of fuel and do a good job of purifying the surrounding air.
The team calculated that in one day, 360 of these leaves – each measuring 170 cm long and 20 cm wide (67 x 7.9 in) – could be capable of producing half a ton of carbon monoxide, and pulling 10 percent of the carbon dioxide out of the air for about 100 m (328 ft) around the setup.
"By enveloping traditional artificial leaf technology inside this specialized membrane, the whole unit is able to function outside, like a natural leaf," says Singh. "Our conceptual design uses readily available materials and technology, that when combined can produce an artificial leaf that is ready to be deployed outside the lab where it can play a significant role in reducing greenhouse gases in the atmosphere."
The research was published in the journal ACS Sustainable Chemistry & Engineering.
