Recycling of materials has been going on for, well since ever, but more recent concerns have focussed on industrial scale recycling of metals, plastics and other items. However, there are the unloved things that are harder, and more expensive to recycle.

Take, for example, car battery acid.

Now researchers have developed a solar-powered reactor that uses acid recovered from old car batteries to break down hard-to-recycle forms of plastic waste such as drinks bottles, nylon textiles and polyurethane foams and convert them into hydrogen fuel and industrial chemicals.

The reactor, developed by the University of Cambridge, employs a photocatalyst that is robust enough to withstand the highly corrosive effects of acid, while making productive use of the acid inside spent car batteries, which is normally neutralised 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.”

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 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.

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