Solar-powered reactor uses CO2 to make sustainable fuel

Researchers at the University of Cambridge have developed a reactor that pulls carbon dioxide directly from the air and converts it into sustainable fuel, using sunlight as the power source.

The researchers say their solar-powered reactor, which they describe in the journal Nature Energy, could be used to make fuel to power cars and planes, or the many chemical and pharmaceutical products we rely on. It could also be used to generate fuel in remote or off-grid locations.

Carbon capture and storage (CCS) has been touted as a possible solution to the climate crisis, and has recently received £22 billion in funding from the UK Government. However, CCS is energy-intensive and there are concerns about the long-term safety of storing pressurised CO₂ deep underground, although safety studies are currently being carried out.

“Aside from the expense and the energy intensity, CCS provides an excuse to carry on burning fossil fuels, which is what caused the climate crisis in the first place,” said Professor Erwin Reisner, who led the new research. “CCS is also a non-circular process, since the pressurised CO₂ is, at best, stored underground indefinitely, where it’s of no use to anyone.”

“What if instead of pumping the carbon dioxide underground, we made something useful from it?” added first author Dr Sayan Kar, from Cambridge’s Yusuf Hamied Department of Chemistry. “CO₂ is a harmful greenhouse gas, but it can also be turned into useful chemicals without contributing to global warming.”

The focus of Reisner’s research group is the development of devices that convert waste, water and air into practical fuels and chemicals. These devices take their inspiration from photosynthesis: the process by which plants convert sunlight into food. The devices don’t use any outside power — all they need is the sun.

The team’s newest system takes CO₂ directly from the air and converts it into syngas: a key intermediate in the production of many chemicals and pharmaceuticals. This approach is much easier to scale up than earlier solar-powered devices, the researchers claim, as it does not require any transportation or storage.

The solar-powered flow reactor uses specialised filters to grab CO₂ from the air at night, like how a sponge soaks up water. When the sun comes out, the sunlight heats up the captured CO₂, absorbing infrared radiation, and a semiconductor powder absorbs the ultraviolet radiation to start a chemical reaction that converts the captured CO₂ into solar syngas. A mirror on the reactor concentrates the sunlight, making the process more efficient.

The researchers are currently working on converting the solar syngas into liquid fuels, which could be used to power cars, planes and more — without adding more CO₂ to the atmosphere.

“If we made these devices at scale, they could solve two problems at once: removing CO₂ from the atmosphere and creating a clean alternative to fossil fuels,” Kar said. “CO₂ is seen as a harmful waste product, but it is also an opportunity.”

The researchers say that a particularly promising opportunity is in the chemical and pharmaceutical sector, where syngas can be converted into many of the products we rely on every day, without contributing to climate change. They are building a larger scale version of the reactor and hope to begin tests soon.

If scaled up, the researchers say their reactor could be used in a decentralised way, so that individuals could theoretically generate their own fuel, which would be useful in remote or off-grid locations.

“Instead of continuing to dig up and burn fossil fuels to produce the products we have come to rely on, we can get all the CO₂ we need directly from the air and reuse it,” Reisner said. “We can build a circular, sustainable economy — if we have the political will to do it.”

This is a modified version of a news item published by the University of Cambridge under CC BY-NC-SA 4.0.

Image caption: The solar-powered flow reactor. Image credit: Sayan Kar.