Solar-powered fuel cell recycles plastic waste and carbon dioxide

A solar-powered device could help remove carbon dioxide from the air and convert plastic waste into sustainable fuel and useful chemicals, in a double-whammy of recycling.

Previous research on solar fuel cells, a technology that uses sunlight to drive chemical reactions that produce fuels, have used pure CO2. Now, Erwin Reisner at the University of Cambridge and his colleagues have developed a device that utilises CO2 captured from industrial processes or directly from the air, filtering out other gases as needed.

“There has been a tremendous advance in developing carbon capture and sequestration technologies. In parallel, there’s been a lot of development in solar fuels devices,” says Reisner. “This is the first time combining the two.”

The device is split into two compartments. One filters air though an alkaline solution that catches CO2, then converts it into syngas, a fuel that is usually used to make ammonia or methanol. In the other, a solution derived from PET plastic waste gets converted into glycolic acid, a chemical that is commonly used in cosmetics.

Combining these two compartments isn’t just a case of creating a two-in-one gadget because the pair actually work together. For CO2 to transform into syngas, it needs to gain some electrons. Typically, this is done by breaking up water molecules, but that process is energy-intensive, says Reisner. Instead, the two compartments act like a battery, with the CO2 side the cathode and the plastic side the anode, transferring electrons between them.

As a proof-of-concept prototype, the technology still has a long way to go before it can be deployed at a large scale. “One of the things we are trying to improve is the efficiency,” says team member Sayan Kar, also at the University of Cambridge.

In the future, the researchers hope that the technology will help eradicate new fossils fuels from the economy entirely. “The process is completely circular,” says Reisner. “We capture CO2. We make a fuel. You use it. You form the CO2 again.”

Reisner also notes that this demonstrates there is an alternative to just to capturing CO2 and storing it in places like underground reservoirs. “You pump it somewhere, but we don’t know the long-term consequences. Now, we show you can actually make useful products from it.”

“It is a nice chemistry, but it’s difficult to say if it would compete with existing processes,” says Jotheeswari Kothandaraman at Pacific Northwest National Laboratory in Washington state. “Techno-economic and life cycle assessments are needed to know the economic feasibility and carbon footprint of the approach.”