Clean hydrogen created from plastic waste using battery acid from old cars and solar power – Image for illustrative purposes only (Image credits: Flickr)
Global plastic production surpasses 400 million tonnes annually, yet only 18 percent finds its way into recycling streams. Much of the remainder ends up in landfills, incinerators, or the environment. Researchers at the University of Cambridge have introduced a solar-powered process that addresses this alongside another waste challenge: acid from discarded car batteries.[1][2]
Addressing Interconnected Waste Streams
Spent car batteries represent a massive volume of hazardous waste worldwide. After lead extraction for resale, the remaining sulfuric acid – typically 20 to 40 percent of the battery’s volume – gets neutralized and discarded. This step carries environmental costs and overlooks a potential resource.
The Cambridge team reframes this acid as a tool for tackling plastic pollution. Hard-to-recycle plastics, such as those in drinks bottles, nylon textiles, and polyurethane foams, often evade standard recycling due to contamination or mixed composition. By pairing these wastes, the process creates a circular system where one resolves the issues of the other.[1]
Professor Erwin Reisner, who led the research in Cambridge’s Yusuf Hamied Department of Chemistry, noted the serendipity involved. “The discovery was almost accidental,” he said. “We used to think acid was completely off limits in these solar-powered systems, because it would simply dissolve everything. But our catalyst didn’t – and suddenly a whole new world of reactions opened up.”[1]
The Science Behind Acid Photoreforming
The method, termed solar-powered acid photoreforming, begins with treating plastic waste using the recovered battery acid. This depolymerizes long polymer chains into smaller chemical building blocks, such as ethylene glycol. Sunlight then activates a specially engineered photocatalyst, converting these intermediates into hydrogen gas and valuable chemicals like acetic acid.
Lead author Papa K. Kwarteng, a PhD candidate in Reisner’s group, developed the key photocatalyst. It withstands the corrosive acid environment that previously doomed similar solar systems. “Acids have long been used to break plastics apart, but we never had a cheap and scalable photocatalyst that could withstand them,” Kwarteng explained. “Once we solved that problem, the advantages of this type of system became obvious.”[2]
The acid itself remains reusable throughout the process, avoiding consumption or the need for neutralization. Laboratory tests confirmed its efficacy with both pure acid and that recovered directly from batteries after lead removal.
Robust Performance in Extended Trials
In demonstrations, the reactor operated continuously for over 260 hours with no decline in performance. It delivered high yields of clean hydrogen alongside selective production of acetic acid, a precursor to vinegar and other industrial products. These outcomes suggest potential cost savings over traditional photoreforming, thanks to boosted hydrogen rates and acid recycling.[1]
The system extends beyond common polyethylene terephthalate (PET) to tougher plastics like nylons and foams. This versatility targets materials with few current reuse options, complementing rather than replacing mechanical recycling.
What Matters Now: This approach valorizes two underutilized wastes, producing fuel without added emissions. It highlights how targeted chemistry can bridge gaps in circular economies.
Engineering Hurdles on the Horizon
While the fundamental chemistry proves reliable, scaling remains the next frontier. Building durable reactors to manage corrosive conditions and process real-world, impure waste demands further innovation. Kwarteng emphasized practicality: “These acids are already handled safely in industry. The question now is engineering: how do we build reactors that can run continuously and handle real-world waste?”[1]
The researchers do not claim a universal fix for plastic woes. Instead, they position the technology as a targeted solution for problematic streams. Support from Cambridge Enterprise and UK research funding will aid commercialization efforts.
A Step Toward Waste as Resource
This work demonstrates the potential in reimagining waste not as a burden, but as feedstock for clean energy. Reisner captured the promise: “The fact we can create value from plastic waste using sunlight and discarded battery acid makes this a really promising process.”[2] As engineering advances, such integrations could quietly reshape how societies handle mounting waste volumes, one reactor at a time.