Cambridge team builds solar reactor that turns plastic waste into hydrogen using car battery acid

Cambridge: Researchers at the University of Cambridge have developed a solar-powered reactor that breaks down hard-to-recycle plastics and converts them into clean hydrogen fuel and industrial chemicals, using acid recovered from old car batteries.

The reactor runs on sunlight and offers a potentially cheaper, more sustainable alternative to current chemical recycling methods. The team says the process could create a circular system where one waste stream helps solve another. Results were published in the journal Joule.

Global plastic production exceeds 400 million tonnes per year, yet only 18% is recycled. The rest is burned, landfilled, or escapes into ecosystems. The new method, known as acid photoreforming, targets tough waste streams like drinks bottles, nylon textiles, and polyurethane foams.

The breakthrough came when researchers found their photocatalyst could withstand highly corrosive acid. That opened the door to reusing acid from spent car batteries, which is normally neutralized and discarded.

“The discovery was almost accidental,” said Professor Erwin Reisner from Cambridge’s Yusuf Hamied Department of Chemistry, who led the research. “We used to think acid was completely off limits in these solar-powered systems, because it would simply dissolve everything. But our catalyst developed didn’t, and suddenly a whole new world of reactions opened up.”

Lead author Kay Kwarteng, a PhD candidate in Reisner’s group, developed the photocatalyst. “Acids have long been used to break plastics apart, but we never had a cheap and scalable photocatalyst that could withstand them,” Kwarteng said. “Once we solved that problem, the advantages of this type of system became obvious.”

The method first treats waste plastics with car battery waste acid, breaking long polymer chains into chemical building blocks such as ethylene glycol. The photocatalyst then converts those compounds into hydrogen and acetic acid, the main ingredient in vinegar, when exposed to sunlight.

Researchers say acid photoreforming could help address the global mountain of plastic waste while producing useful fuel and chemicals powered by the Sun.