Researchers at the University of Cambridge have operated a solar-powered plastic recycling reactor at one square metre under natural sunlight — a fourfold linear scale-up from the 25cm-square laboratory devices used in earlier demonstrations and the first time the technology has run outdoors with scalable fabrication techniques.

The system, tested outside Cambridge's Chemistry Department, does not generate electricity like a conventional photovoltaic panel. Instead, it drives a chemical reaction — photoreforming — that converts waste polymers and water into hydrogen fuel and industrial chemical byproducts. The work is published in Nature Chemical Engineering.

The reactor accepts feedstock ranging from cellulose to PET beverage bottles. For an industry that processes PET at millions of tonnes per year, the feedstock flexibility matters: photoreforming does not require clean, sorted, monomaterial streams of the kind mechanical recyclers depend on.

From dip-coating to spray-coating

Earlier versions of the photocatalyst panels relied on high temperatures, harsh chemicals or complex manufacturing. Typically, small catalyst particles were suspended in solution and deposited onto a substrate. That approach collapses at industrial scale.

"When we started trying to scale this technology up, we quickly found out that what seems simple on a small scale is not simple at all when you're trying to make it at scale," said co-first author Ariffin Bin Mohamad Annuar of Cambridge's Yusuf Hamied Department of Chemistry. "We can't really have giant vats of solution to make these panels – it's just not practical at scale."

The new process assembles panels at room temperature without specialist equipment. A light-absorbing material is sprayed onto a glass panel — using a sprayer comparable to a household paint sprayer — and the panel is then coated with specially designed molecules containing cobalt and zirconium. Professor Dominic Wright's group in the same department synthesised the molecular precursors; Professor Erwin Reisner's team loaded them into the sprayer.

"What surprised me was, after all the optimisation, just how simple it is," said Mohamad Annuar. "We just have this huge panel, we spray our catalyst on it, put it into our solution, put it under the sun, and it produces hydrogen and other valuable chemicals just from plastic waste. It's just simple and scalable."

The researchers also carried out a cost analysis of what commercial scale-up would realistically require — which they describe as a first for this class of research. The spray-coating route cuts reactor production costs sharply, a prerequisite for manufacturing at volume.

A second catalyst closes the conversion gap

In a companion paper in Energy & Environmental Science, the Reisner lab addresses a persistent weakness in PET photoreforming: the hydrogen-generating side of the reaction has advanced faster than the plastic-degradation side, leaving inefficient processes and messy byproducts.

The team's new palladium-based catalyst — a bifunctional Pd-Al:SrTiO3 photocatalyst sheet — performs both jobs at once, converting ethylene glycol, a chemical derived from PET, into valuable products while generating hydrogen under sunlight. The group also tested this catalyst outdoors at metre-square scale, then used the field data to model costs, energy use and environmental footprint of the process.

"If we're really going to change the way we deal with the twin problems of plastic pollution and clean energy generation, we've got to develop a very scalable way to make these photocatalyst materials and reactors — and show that they really work outdoors," said Reisner, who led the research.

Commercialisation status

The technology remains at demonstrated outdoor prototype stage, not built capacity. The researchers state plainly that reactor durability and efficiency must improve before commercial production is viable; neither paper reports continuous-run lifetimes or throughput in tonnes processed.

Cambridge Enterprise, the university's commercialisation arm, has filed patents covering both technologies. Funding came in part from the UK Department for Science, Innovation and Technology, the Royal Academy of Engineering and Petronas — a signal of petrochemical-sector interest in waste-to-hydrogen routes.

What happens next depends on the gap between a one-square-metre panel and an industrial reactor field: the durability and efficiency targets the Cambridge team has set itself, and whether the filed patents convert into a licensed, bankable plant.