Clean hydrogen created from plastic waste using battery acid from old cars and solar power – Image for illustrative purposes only (Image credits: Unsplash)
Cambridge, United Kingdom – A solar-powered reactor at the University of Cambridge operated continuously for more than 260 hours, converting hard-to-recycle plastic waste and acid from discarded car batteries into clean hydrogen fuel and useful chemicals.[1][2] Researchers hailed the process as a promising step toward upcycling two major waste streams simultaneously. The innovation addresses the global plastic crisis, where over 400 million tonnes are produced yearly but only 18 percent recycled.[1]
The Ingenious Chemistry Behind the Reactor
Scientists developed a method called solar-powered acid photoreforming to achieve this feat. They first treated plastic waste with sulfuric acid recovered from old car batteries, which contain 20 to 40 percent acid by volume.[1] This step broke down the plastics’ long polymer chains into smaller building blocks, such as ethylene glycol from polyethylene terephthalate, or PET.
A specially engineered photocatalyst then took over under sunlight. Composed of cyanamide-functionalized carbon nitride integrated with cobalt-promoted molybdenum disulfide, the precious-metal-free material withstood the harsh acidic conditions.[3]00031-0) Exposure to solar light or targeted LEDs triggered the conversion of these intermediates into hydrogen gas and acetic acid, a key industrial chemical and vinegar component. The acid remained reusable, enhancing the system’s efficiency.
Targeting Plastics That Defy Conventional Recycling
Current recycling struggles with certain plastics, often resorting to incineration, landfilling, or environmental release. The Cambridge reactor targeted precisely these challenges, processing materials like PET bottles, nylon textiles, and polyurethane foams.[1] Nylon and polyurethane, in particular, resist mechanical or standard chemical recycling due to their complex structures.
Lead author Papa K. Kwarteng, a PhD candidate in Professor Erwin Reisner’s group, noted the significance. “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.”[1] The process opened new avenues for upcycling contaminated or mixed plastics overlooked by traditional methods.
Lab Results Showcase Stability and Yield
Laboratory tests demonstrated the reactor’s reliability. Under simulated sunlight, it produced 0.35 millimoles of hydrogen per gram of catalyst from PET hydrolysate. Targeted 405 nm LED irradiation boosted yields to 1.9 millimoles per gram for PET, 2.1 for nylon 66, and 4.2 for polyurethane in 24 hours.[3]00031-0)
| Plastic Type | Hydrogen Yield (mmol/g catalyst, 24h LED) | Main Byproduct |
|---|---|---|
| PET | 1.9 | Acetic acid (89% selectivity) |
| Nylon 66 | 2.1 | Pentanoic acid |
| Polyurethane | 4.2 | Acetic acid |
[3]00031-0)
The system achieved up to 40 percent conversion of ethylene glycol with a 9 percent quantum yield. Over 11 days and eight cycles, the catalyst showed no significant degradation, maintaining high selectivity for acetic acid.[4] Researchers even scaled up to three grams of PET in initial trials.
Circular Upcycling Meets Economic Promise
Car batteries represent an overlooked resource. Millions are discarded annually worldwide; after lead recovery, the acid is usually neutralized at environmental cost. This reactor repurposed it directly, creating a closed loop.[1]
- Breaks down plastics without consuming the acid.
- Generates clean hydrogen for fuel cells or industry.
- Produces marketable chemicals like acetic acid.
- Potentially reduces photoreforming costs by an order of magnitude.
“The fact we can create value from plastic waste using sunlight and discarded battery acid makes this a really promising process,” said Professor Reisner.[1] A technoeconomic analysis suggested profitability at ton-scale, driven by product sales.
Engineering the Path to Real-World Impact
While lab success is clear, challenges persist. Building corrosion-resistant reactors for continuous operation and handling diverse real-world waste requires further engineering. The team emphasized complementarity to existing recycling, not a total replacement.
Supported by UK funding bodies, the researchers now pursue commercialization through Cambridge Enterprise. Reisner cautioned realism: “We’re not promising to fix the global plastics problem. But this shows how waste can become a resource.” As plastic production triples by 2060, such innovations could play a vital role in sustainable energy and waste management.[5]