Scientists are getting closer to producing clean hydrogen fuel using nothing but sunlight and a sheet of material just one atom thick, thanks to a breakthrough study exploring how atomically thin materials turn light into chemical energy — with extraordinary precision.
A team of researchers has taken an unprecedented look at where and how this reaction happens on monolayer molybdenum disulphide (MoS₂) — a so-called two-dimensional (2D) material that’s just a single layer of atoms thick. Their findings could help engineer better catalysts for solar-driven hydrogen production, paving the way for cleaner fuels without relying on expensive metals or complex systems.
A Material That’s Only an Atom Thick
MoS₂ belongs to a class of materials known as 2D semiconductors. These ultra-thin crystals have already revolutionised fields like electronics and quantum computing, but they’re also emerging as powerful tools for clean energy — particularly in photocatalysis, the process of using light to drive chemical reactions.
Their appeal lies in their simplicity and scalability: being just one atom thick, they expose all of their surface to the surrounding environment, making every part potentially reactive. But until now, scientists didn’t know exactly where on the material these light-driven reactions happened — or how efficient they were.
Shining a Light, Literally and Figuratively
To crack this mystery, the team used a cutting-edge technique called scanning photoelectrochemical microscopy (SPECM). Think of it like using a super-precise “chemical camera” to map the activity on the surface of MoS₂ while it’s illuminated.
What they discovered is that the reactions are not spread evenly across the material. Instead, different parts of the flake specialise in different jobs: some areas are hotspots for oxidation reactions (where molecules lose electrons), while others are better for reduction (where electrons are gained — such as producing hydrogen from water).
A Tale of Two Charge Carriers
When light hits the MoS₂, it generates pairs of charges: electrons and their positively charged counterparts, known as holes. The researchers found that the holes tend to stay put — near the spot where the light hits — while the electrons travel surprisingly long distances, sometimes more than 80 microns (that’s about the width of a human hair, a long way at this scale).
This means that the exact location where the material is illuminated determines which chemical reaction takes place and where. It’s a bit like aiming a torch at one side of a seesaw and watching it tip the other end.
Not All Light Is Equal
The team also tested how different colours of light affected the material’s behaviour. It turns out that while high-energy blue light (around 455 nm wavelength) created more free-moving charges, redder light (660 nm) led to more efficient chemical reactions. This is because red light creates tightly bound charge pairs, known as excitons, that are more likely to result in useful chemistry rather than just fizzling out.
In short: more light doesn’t always mean better performance — it depends on the type of light and how the material handles it.
What This Means for Clean Energy
These discoveries have major implications. For one, they show that the design of photocatalysts for solar hydrogen production needs to consider not just the material itself, but how it’s lit, where the reactions take place, and how efficiently different parts of the material absorb and convert light.
It also suggests that bigger, better-designed flakes of MoS₂ — or similar 2D materials — could significantly boost the production of hydrogen without needing expensive additives or co-catalysts. That’s a big step towards making green hydrogen a viable part of our energy future.
Looking Ahead
This research isn’t just a win for MoS₂. It demonstrates how precise mapping of photocatalytic activity can guide the development of a whole new generation of materials, finely tuned to turn sunlight into storable, usable energy.
It’s a reminder that sometimes, the biggest breakthroughs happen on the smallest scales — just a single atom thick.
Source
Spatially resolved photocatalytic active sites and quantum efficiency in a 2D semiconductor, Nature Communications, 2025-07-26
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