A research group at the University of Cambridge has shown that a solar reactor which produces hydrogen from waste can be built cheaply, made large, and run outdoors — not just on a laboratory bench. Reported in Nature Chemical Engineering, the work addresses the question that usually decides whether a promising catalyst ever leaves the lab: can you scale the device up, and does it still work under a real sky?
For SPIN readers this is a familiar research line. In May we covered an earlier reactor from the same Cambridge lab that turned plastic waste and spent battery acid into hydrogen and acetic acid. The new study is the next step: the same photocatalytic principle, now engineered so the light-harvesting panels can be manufactured simply and enlarged almost at will.
A photocatalyst you can spray on
Unlike a solar cell, the reactor does not generate electricity. It uses sunlight directly to drive a chemical reaction that releases hydrogen from dissolved waste. The advance from the team, led by Ariffin Bin Mohamad Annuar, is a way to apply the two functional layers — a light-absorbing layer and a catalyst layer containing cobalt and zirconium — onto glass plates with a simple spray gun, at room temperature and without specialist equipment. That removes the high temperatures, aggressive chemicals and intricate fabrication steps that had kept earlier photo-reforming reactors stuck at bench scale.
To prove the point, the researchers assembled a one-square-metre reactor from four coated plates, floated them in a shallow tray of waste solution, and placed it in the sun outside the Cambridge chemistry building. The appeal, they stress, is precisely how ordinary the process is: spray the catalyst onto a large plate, immerse it in the waste solution, and leave it in the sunlight.
Promising — but a long way from cheap hydrogen
The output figures are modest and reported honestly. Over six hours in the sun, one square metre of reactor produced about 1.51 millimoles of hydrogen from pretreated cellulose, and 5.24 millimoles when fed pure glucose. Alongside the hydrogen, the reaction yielded useful platform chemicals — formate, acetate and glycolate. Shredded, pretreated PET bottles gave a lower yield than cellulose in a small laboratory reactor and were not run in the outdoor unit.
The economics remain the sticking point. On the measured performance, the team calculated that a millimole of hydrogen from glucose would cost roughly £0.93 (about €1.08) — far above conventional hydrogen, which can be produced for a fraction of a cent for the same amount. The authors expect costs to fall with industrial-scale implementation and with revenue from the co-produced chemicals, but the durability and efficiency of the reactors remain open challenges, and the feedstocks still need shredding and chemical pretreatment before use.
Why it matters for Power-to-X
This is not electrolysis, and the hydrogen it makes is not the electrolytic, renewable-electricity-based hydrogen — the RFNBOs — at the centre of most Power-to-X roadmaps. It is a different, complementary route: sunlight driving chemistry directly, with a waste stream as the electron source and saleable chemicals as a by-product. For a field built on turning renewable energy and recycled carbon into fuels and molecules, a solar-to-hydrogen process that also upcycles plastic and biomass waste is worth watching — even if, on today’s numbers, its contribution is still scientific rather than commercial. Cambridge has now shown that scale need not be the blocker; cost and longevity are the next tests. But what about the costs of doing nothing?…
Source: Ariffin Bin Mohamad Annuar et al., Nature Chemical Engineering (2026), doi:10.1038/s44286-026-00406-y; reported by bild der wissenschaft.
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