Professor Reisner and Mr. Kwarteng, who led the research © University of Cambridge, licensed according to CC 4.0. BY-SA
Researchers have developed a solar-powered reactor to break down hard-to-recycle forms of plastic waste – such as drinks bottles, nylon textiles and polyurethane foams – using acid recovered from old car batteries.
The process then converts the waste into clean hydrogen fuel and valuable industrial chemicals.
The reactor was developed by researchers from the University of Cambridge and powered powered by the energy from the Sun, making it a potentially cheaper, more sustainable alternative to current chemical-based recycling methods.
The team say their method could create a circular system where one waste stream solves another. Their results are reported in the journal Joule.
Global plastic production exceeds 400 million tonnes per year, yet only 18% is recycled, Cambridge state in a press release on the discovery. The rest is burned, landfilled, or escapes into ecosystems. The researchers say that their method, known as acid photoreforming, could help address the global mountain of plastic waste.
In an “almost accidental” discovery, the photocatalyst they invented turned out to be robust enough to withstand the highly corrosive effects of acid, opening a world of possibilities in the process including the chance to make productive use of the acid inside 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.”
“Acids have long been used to break plastics apart, but we never had a cheap and scalable photocatalyst that could withstand them,” said lead author Kay Kwarteng, a PhD candidate in Reisner’s research group, who developed the photocatalyst. “Once we solved that problem, the advantages of this type of system became obvious.”
The method developed by Kwarteng, Reisner and their colleagues, first treats waste plastics with the car battery waste acid, breaking the long polymer chains into chemical building blocks such as ethylene glycol, which the photocatalyst then converts into hydrogen and acetic acid (the main ingredient in vinegar) when exposed to sunlight.
In laboratory tests, the reactor generated high hydrogen yields and produced acetic acid with high selectivity. It also ran for more than 260 hours without any loss in performance.
The approach works for multiple types of plastic waste, even those that are currently tough to recycle, such as nylon and polyurethane. This offers a real advancement to current upcycling technologies that do not cover plastics beyond PET.
The approach works not just with new, laboratory-grade acid, but with the acid recovered from car batteries. These batteries contain between 20-40% acid by volume, and are replaced worldwide in huge numbers every year. The lead in these batteries is typically extracted for resale, but the acid creates extra waste once it is safely neutralized.
“It’s an untapped resource,” said Kwarteng. “If we can collect the acid before it’s neutralized, we can use it again and again to break down plastics: it’s a real win-win, avoiding the environmental cost of neutralizing the acid, while putting it to work generating clean hydrogen.”
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The researchers say their method offers a potential order‑of‑magnitude cost reduction compared with other photoreforming approaches, largely because the acid enables increased hydrogen production rates and can be reused rather than consumed or wasted.
Kwarteng says that although challenges remain—such as ensuring reactors can withstand corrosive conditions—the fundamental chemistry is sound.
“These acids are already handled safely in industry,” he said. “The question now is engineering: how do we build reactors that can run continuously and handle real‑world waste?”
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“We’re not promising to fix the global plastics problem,” said Reisner. “But this shows how waste can become a resource. The fact we can create value from plastic waste using sunlight and discarded battery acid makes this a really promising process.”
The team plans to commercialize this process with the support of Cambridge Enterprise, the University’s innovation arm, while the research itself was supported by a broad collective of trusts, institutes, and other funding sources which can be found in the press release.
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