The zero-emissions option of hydrogen fuel holds a lot of promise for reducing our reliance on fossil fuels - if only we could find a way to produce it cheaply and without needing insane amounts of energy input. Now, scientists have found a way to efficiently produce hydrogen fuel by using rust and a light source.
The set-up uses just a few basic ingredients - light from a mercury-xenon lamp, a solution of water and methanol, and a particular type of rust (or iron oxide) called α-FeOOH. In a new study, researchers have outlined how this method yields 25 times more hydrogen than existing techniques that use titanium dioxide catalysts.
One of the biggest challenges in hydrogen fuel production is teasing hydrogen atoms apart from other molecules, and keeping them that way without the entire thing blowing up.
In the new method, by swapping titanium with rust, the hydrogen gas generated seemed to be blocked from recoupling with oxygen, making the separation of the elements easier, and reducing the risk of explosion at the same time.
That flammability is one of the reasons that hydrogen fuel hasn't yet caught on. The other is that getting the hydrogen to separate (from water, methane or something similar) usually takes up a lot more energy than is practically viable.
"We were really surprised at the generation of hydrogen using this catalyst, because most of the iron oxides are not known to reduce to hydrogen," says materials scientist Ken-ichi Katsumata, from the Tokyo University of Science in Japan.
"Subsequently, we searched for the condition for activating α-FeOOH and found that oxygen was an indispensable factor, which was the second surprise because many studies showed that oxygen suppresses hydrogen production by capturing the excited electrons."
As well as being more common (and therefore cheaper) than other metals used as catalysts to produce hydrogen, this type of rust also seems to be very stable too – the researchers report that they were able to keep their lab experiments going successfully for an astonishing 400 hours.
Considering the source for the hydrogen in this case is simple organic waste, the new approach could potentially make a huge difference to energy systems – a hydrogen production process that does more with less.
Whether in a car engine or power plant, the only by-product from hydrogen fuel is water. It's this promise of a revolutionary fuel source that has many scientists working hard on generating hydrogen using abundant resources like water and sunlight.
We've seen several catalysts successfully tested in recent years, giving experts a number of avenues to explore, but the challenge of getting something that makes sense commercially has yet to be overcome.
This latest study describes a significant step forward, but plenty more research is going to be required before we can power our cars with hydrogen. One of the areas the team wants to investigate next is why oxygen is so crucial to the production process (when it was removed from the catalyst, the experiments failed).
"The specific function of the oxygen in activating light-induced α-FeOOH has not been unveiled yet," says Katsumata. "Therefore, exploring the mechanism is the next challenge."
The research has been published in Chemistry – A European Journal.