If ammonia has been invited into research and development for hydrogen mobility, it is not without reason. We can quite easily imagine cars, light commercial vehicles and even heavy-duty fuel cell vehicles filling up their tanks from compressed H2 gas dispensers installed in stations that are ultimately very close to those that deliver petrol and diesel.
For large ships and airplanes, such a scenario does not appear to be desirable or even conceivable. The space taken up by the containers would be too large and the volumes loaded too dangerous. Hence the use of liquid ammonia, easy to store and transport, which is becoming more and more necessary for traveling by air and on water. With the chemical formula NH3, this product is made up of 3 molecules of hydrogen for one of nitrogen, which can be split into 2 gases by catalysis.
Get rid of critical materials
Since nitrogen gas is one of the main elements present in the air, scientists believe that simply releasing it into the atmosphere during the reaction is not a problem. On the other hand, hydrogen can be used to power large electric or thermal motors such as turbines. The problem is that the usual catalysts use expensive and sometimes critical materials, such as palladium, platinum, rhodium and ruthenium.
To accelerate the reactions, they are subjected to high temperatures which amount to hundreds or even thousands of degrees, using fossil fuels. All this therefore has a financial and environmental cost that we now want to erase as much as possible. And this, to face the urgency of climate change to be treated in part by the decarbonization of transport and industry.
A team made up of researchers from 3 American establishments (Nanophotonics Laboratory at Rice University in Houston, Andlinger Center for Energy and the Environment at Princeton University, and the company Syzygy Plasmonics) has developed a much more interesting method.
It was already known that it is possible to use a copper-iron catalyst to decompose ammonia into hydrogen and nitrogen. Except that the yield is poor, with a reactivity 300 times lower than that obtained with a copper-ruthenium catalyst, the latter being hitherto known as the best thermocatalyst for this reaction.
The team of researchers, energized in particular by Naomi Halas, Peter Nordlander, Hossein Robatjazi and Emily A. Carter, discovered that by subjecting the copper-iron catalyst to light, a reactivity similar to that of copper- ruthenium with antenna plasma reactors.
In the Rice University lab, the light came from lasers. By continuing and diversifying the tests, Syzygy Plasmonics has demonstrated that lighting with simple off-the-shelf LEDs is sufficient to obtain the same result very precisely. Having mobilized significant resources, their experimentation was carried out on a scale 500 times greater than that of the Texas scientific establishment.
A new path opened
Not only does the new method make it possible to dispense with critical and expensive materials, but it also eliminates the need for high temperature which greatly increased the bill for obtaining hydrogen from ammonia.
This discovery is a real victory for Naomi Halas and Peter Nordlander, both holders of a chair and scientific professors at Rice University, but also co-founders of the company Syzygy Plasmonics. For years they have believed that light can play a key role in the catalysis of liquid ammonia, working tirelessly on this subject. Good results could already be obtained, but by mobilizing precious metals such as gold or silver. The research has benefited from investments from the US government and industry coming together to create infrastructure and markets for a low-carbon fuel based on liquid ammonia.
” This discovery paves the way for sustainable, low-cost hydrogen that could be produced locally rather than in large centralized plants », rejoices Peter Nordlander. The opening of this new way suggests that other combinations of common and inexpensive metals could be employed in the same way.
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This revolutionary process produces low-cost green hydrogen from ammonia
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