Researchers from the University of New South Wales (UNSW) and the University of Sydney (USYD) have put their big heads together and managed to produce ‘green’ ammonia from air, water, and solar energy in a fashion that does not also require high temperatures, high pressure, and enormous amounts of infrastructure. The researchers believe the new production method, which has so far only been demonstrated in a lab, could play a role in the global transition to a hydrogen economy.
Ammonia, a hydrogen product, is currently used mainly in the fertilizer industry, but could play a pivotal role in the evolving hydrogen economy, particularly as a shipping fuel in its liquefied form. This, says Rystad Energy’s head of global energy systems, Marius Foss, is for the simple reason that ammonia can be safely liquefied at only 33 C – making it much easier and more efficient to store and transport than H2.
However, the traditional way to make ammonia, the Haber-Bosch process, is only cost-effective at enormous scale, expense and emissions. “The current way we make ammonia via the Haber-Bosch method produces more CO2 than any other chemical-making reaction. In fact, making ammonia consumes about 2 percent of the world’s energy and makes 1 percent of its CO2 – which is a huge amount if you think of all the industrial processes that occur around the globe,” says UNSW’s School of Chemical Engineering lecturer Emma Lovell.
Lovell added that the carbon footprint of the Haber-Bosch process is amplified because such a large-scale project requires a centralized location, which necessarily entails a great deal of global transportation. Moreover, as was shown with the catastrophic ammonium nitrate explosion at a warehouse in Beirut last year, storing large amounts of ammonia in one place is very dangerous.
However, Lovell and her team have found a way to produce ammonia cheaply, locally, and cleanly. Indeed, Lovell believes that once the technology is available commercially, farmers will be able to produce their own green ammonia to make fertilizer on site.
“So if we can make it locally to use locally, and make it as we need it, then there’s a huge benefit to society as well as the health of the planet,” says Lovell.
The key to this breakthrough is found in the fourth state of matter – plasma. According to ARC DECRA fellow and research co-author, Ali Jalili, converting atmospheric nitrogen (N2) directly to ammonia using electricity “has posed a significant challenge to researchers for the last decade, due to the inherent stability of N2 that makes it difficult to dissolve and dissociate.”
However, by using plasma (a form of lightning in a tube) Jalili and his colleagues were able to convert air into an intermediary called NOx (either NO2 or NO3) which is more reactive than N2 in the air.
“Once we generated that intermediary in water, designing a selective catalyst and scaling the system became significantly easier,” says Jalili. “The breakthrough of our technology was in the design of the high-performance plasma reactors coupled with electrochemistry.”
The team of researchers may have solved the problem of storing and transporting hydrogen. Rose Amal, a professor at UNSW and the ARC Training Centre for Global Hydrogen Economy, said that hydrogen requires an exceptional amount of space for storage, “otherwise you have to compress or liquify it.”
“But liquid ammonia actually stores more hydrogen than liquid hydrogen itself, and so there has been increasing interest in the use of ammonia as a potential energy vector for a carbon-free economy,” says Amal.
This is all to say that allied with this technological breakthrough, ammonia could be made from solar energy and be essentially ready for export.
“We can use electrons from solar farms to make ammonia and then export our sunshine as ammonia rather than hydrogen,” concludes Amal. “And when it gets to countries like Japan and Germany, they can either split the ammonia and convert it back into hydrogen and nitrogen, or they can use it as a fuel.”
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