Acid recovered from spent lead-acid car batteries could be repurposed to enable a new route for recycling difficult plastic waste, according to research published in the journal Joule.
A team at the University of Cambridge has developed a solar-driven process that uses sulphuric acid reclaimed from end-of-life batteries to break down plastics and convert them into hydrogen fuel and valuable chemicals. The work highlights a potential new value stream for battery recyclers, where acid – typically treated as a waste by-product – becomes a feedstock for advanced recycling.
Lead-acid batteries are already one of the most recycled products globally, with the lead routinely recovered and reused. However, the electrolyte – comprising around 20–40% sulphuric acid – has traditionally been neutralised and discarded after recycling.
The Cambridge team’s process instead captures and reuses this acid in what they describe as “solar-powered acid photoreforming”. In the first stage, the recovered acid is used to depolymerise plastics, breaking long polymer chains into smaller molecules such as ethylene glycol. These intermediates are then converted into hydrogen gas and acetic acid using a sunlight-driven photocatalyst.
Professor Erwin Reisner, who led the study, said the work overturns assumptions about using strong acids in photocatalytic systems: “We used to think acid was completely off limits… but our catalyst developed didn’t – and suddenly a whole new world of reactions opened up.”
The researchers engineered a catalyst capable of operating in highly corrosive conditions, overcoming a longstanding barrier to combining acid hydrolysis with solar reforming. Laboratory testing showed the reactor could operate for more than 260 hours without performance loss, while delivering high hydrogen yields and strong selectivity towards acetic acid.
A route to recycling mixed and hard-to-recycle plastics
Importantly, the process can handle mixed and hard-to-recycle plastics – including nylon textiles and polyurethane foams – broadening the scope beyond conventional mechanical recycling streams.
For the lead-acid battery recycling sector, the findings point to a shift in how electrolyte waste is viewed. Rather than a hazardous stream requiring neutralisation, spent acid could become a reusable reagent in adjacent recycling processes. Lead author Kay Kwarteng described the acid as “an untapped resource”, adding that reusing it avoids the environmental cost of neutralisation while enabling the production of clean hydrogen.
The study also suggests potential economic benefits. By integrating recycled acid into the process, the researchers indicate that hydrogen production costs could be reduced compared with other photoreforming approaches, while simultaneously creating value from two waste streams.
While still at laboratory scale, the team is exploring routes to commercialisation. Key challenges include designing reactors capable of handling corrosive conditions in continuous industrial operation and integrating the process with existing waste management infrastructure.
The researchers stress that the technology is not intended to replace established recycling methods, but to complement them – particularly for contaminated or composite plastics that currently lack viable end-of-life solutions.
If scaled successfully, the approach could strengthen links between battery recycling and broader circular economy initiatives, demonstrating how waste streams from mature industries such as lead-acid batteries can support emerging advanced recycling technologies.
Photo: an AI-generated illustration of battery acid dissolving polyurethane foam
