A team at the University of Cambridge has built a solar-powered reactor that turns two waste streams into two useful products at the same time: hard-to-recycle plastic waste and used sulfuric acid from spent car batteries become green hydrogen and acetic acid, driven by sunlight. The results were published in April 2026 in the journal Joule.

How the process works

The method, developed by Prof. Erwin Reisner and PhD candidate Kay Kwarteng at Cambridge’s Yusuf Hamied Department of Chemistry – they call it solar-powered acid photoreforming – runs in two coupled steps:

  1. The sulfuric acid recovered from old car batteries breaks the long polymer chains of plastic waste into chemical building blocks such as ethylene glycol.
  2. A newly developed photocatalyst then converts these building blocks into hydrogen and acetic acid (the main ingredient in vinegar) under sunlight.

The key breakthrough is the photocatalyst itself. In earlier photochemical recycling approaches, acid was considered off-limits because it would simply destroy the catalyst. Kwarteng engineered a photocatalyst that withstands those corrosive conditions – opening a reaction window that had previously been closed.

What the lab results show

In the published experiments, the reactor delivered high hydrogen yields and produced acetic acid with high selectivity. Notably, the system ran for more than 260 hours without any loss in performance. The process works for several types of plastic waste, including those that are currently very hard to recycle – such as nylon textiles and polyurethane foams, which today’s mechanical and chemical recycling routes mostly fail to handle. That is a meaningful step beyond existing upcycling technologies, which are largely limited to PET.

The acid input is also non-trivial. Lead-acid car batteries contain between 20 and 40 percent sulfuric acid by volume and are discarded worldwide in huge numbers. Today, the lead is typically recovered and resold, while the acid is neutralised and disposed of. The Cambridge process uses that otherwise discarded acid as an active reagent – and, according to the researchers, it can be reused multiple times rather than being consumed.

How this fits into the Power-to-X picture

Photoreforming is a direct solar-to-hydrogen route: sunlight drives the reaction without an electrolyser in between. Compared with classical PEM or alkaline electrolysis powered by green electricity, this technology line sits much earlier on the development curve. Its appeal is that it produces value from two waste streams at once: an energy carrier (H2) and an industrial chemical building block (acetic acid).

With global plastic production exceeding 400 million tonnes per year and a recycling rate of around 18 percent, the vast majority remains a burden on ecosystems and the climate. Processes that chemically unlock precisely this hard-to-recycle fraction while producing a clean energy carrier are interesting in a Power-to-X context – even if they will not replace conventional electrolysis-based routes.

SPIN Perspective

This work is a nice example of an angle that often gets too little attention in the PtX debate: thinking in material loops, not in single technologies. When one reactor uses two otherwise discarded waste streams – plastic and battery acid – as inputs and produces two marketable products, the question shifts. It moves from “What does a tonne of hydrogen cost?” to “What system costs can we avoid if a single process replaces recycling, disposal, and hydrogen production at the same time?”

Despite the appeal, honest caveats are in order:

  • Low TRL. The results come from the lab. 260 hours of continuous operation is a good sign for catalyst stability, but a long way from industrial duty cycles.
  • Reactor design is open. Kwarteng frames it directly: “The question now is engineering: how do we build reactors that can run continuously and handle real-world waste?” Corrosion-resistant, large-scale solar reactors are not trivial.
  • Economics are a researcher claim. An “order-of-magnitude” cost reduction over other photoreforming approaches is plausible, but it has not yet been confirmed by independent techno-economic analysis under real-world conditions.
  • Volumes will stay modest. Even if the process scales, the achievable hydrogen volumes will not replace the ramp-up path of large-scale electrolysis projects. At best, they will serve a niche – with the bonus of breaking down plastic waste and producing acetic acid as an industrial chemical along the way.

And that is precisely where the appeal lies: not as a competitor to large-scale electrolysis, but as a possible building block in a system that addresses several defossilisation and circularity goals at the same time. Cambridge Enterprise and a UKRI Impact Acceleration Account are supporting commercialisation. Whether this becomes an industrial solution can only be judged seriously over the coming years.

Sources