Scientists are very keen to find effective ways of getting hydrogen from water, thus unlocking hydrogen's potential as a clean fuel. A newly developed device manages the feat, using only sunlight as a power source.
Using catalytic electrodes and perovskite solar cells fused together in a single unit, the clever contraption can hit sunlight-to-hydrogen efficiency rates as high as 6.7 percent. It just drops into water, and away it goes (when the Sun is out).
It might be a bit too early to start converting all our cars to take zero-emission hydrogen fuel cells, but the researchers behind the new invention say that it should be relatively easy to scale up the technology for wider use.
A cross-section of the catalyst. (Jia Liang)
"The concept is broadly similar to an artificial leaf," says materials scientist Jun Lou, from Rice University in Texas. "What we have is an integrated module that turns sunlight into electricity that drives an electrochemical reaction. It utilises water and sunlight to get chemical fuels."
Perovskite is one of the rising stars of the solar power industry, promising even better results than silicon solar panels if harnessed correctly, and here it's used to power a catalyst to split water up into oxygen and hydrogen. What's more, the device doesn't cost much to build.
Key to the way the device runs is the encapsulation method it uses: the way that the scientists have chosen to add a polymer film around the perovskite, protecting it from damage if submerged in water.
While protecting the solar cell, the polymer also allows sunlight through, and serves as an insulator between the cells and the electrodes. Improvements in this encapsulation and in the solar cell efficiency should be possible with more research, and further down the line the device could even offer a self-sustaining source of energy.
"With a clever system design, you can potentially make a self-sustaining loop," says Lou. "Even when there's no sunlight, you can use stored energy in the form of chemical fuel. You can put the hydrogen and oxygen products in separate tanks and incorporate another module like a fuel cell to turn those fuels back into electricity."
There's still plenty of work to do, but the new device solves a number of problems faced by previous designs – waterproofing the perovskite to some extent means it can be placed directly in the water, for example, speeding up the process. The team has also considered both oxygen and hydrogen extraction, rather than one or the other.
Scientists are busy experimenting with using perovskite and other materials in tandem, to try and improve the amount of electricity we can generate from the Sun.
One of the downsides of using solar cells based on perovskite crystals is that they can be pricey to manufacture, but in this study cheaper alternatives have been swapped in – carbon instead of platinum, for example.
"That lowers the entry barrier for commercial adoption," says Lou. "Integrated devices like this are promising because they create a system that is sustainable."
The research has been published in ACS Nano.