By Angus Dalton July 3, 2025 https://www.smh.com.au/national/nsw...ere-s-why-it-has-to-stop-20250619-p5m8q4.html It’s the chemical reaction that built the world as we know it: the Haber-Bosch process. As our population has grown, so has humanity’s hunger for nitrogen. Plants need it to produce chlorophyll, the green pigment that drives photosynthesis and fuels the growth of apples, wheat, rice, zucchini and almost every other crop that underpins our existence. The effect of the Haber-Bosch process on the world's population Nitrogen fertiliser from the ammonia produced by the industrial Haber-Bosch process is estimated to have allowed billions of more people to exist. Without nitrogen-based fertiliser, the world would support 3.5 billion fewer people, according to some estimates, simply because we couldn’t grow enough food to feed them. Initially, the world fed its raging need for nitrogen with bird poo. Bird and bat droppings are full of the stuff and, throughout the 1800s, demand sparked wars and the annexation by the US of islands splattered with seabird poo, for the pure purpose of mining it like precious metal. An island off Peru where rocks are covered in guano, once the main source of nitrogen and phosphorous for fertiliser before the invention of the Haber-Bosch process.Credit: Danilo Bargen/Wikimedia Commons Then in 1909, industrial chemist Fritz Haber and engineer Carl Bosch invented the Haber-Bosch process, a way of making ammonia by reacting nitrogen and hydrogen together under massive pressures of 400 atmospheres and temperatures of 650 degrees. The process became the world’s main source of nitrogen for fertiliser and was dubbed the “reaction that fed the world”. A 2008 paper in Nature estimated it’s responsible for growing food for 44 per cent of the world’s people. But the reaction that fed the world is now hurting it: the Haber-Bosch process emits CO2 as a byproduct, contributing between 1-2 per cent of global carbon emissions. Now there’s a new act of alchemy in the storied history of an element that underpins the tale of modern humans. P. J. Cullen with his invention at PlasmaLeap, which enables fertiliser to be made with minimal carbon emissions.Credit: Janie Barrett Sydney scientists have harnessed artificial lightning and plasma to create ammonia and ultimately nitrogen fertiliser, out of thin air – and that’s not just significant for farming. It could also quicken ammonia’s path to becoming a carbon-free fuel. Why our hunt for nitrogen is ‘madness’ The irony of our historically violent and now carbon-intensive quest for nitrogen is that, right now, it’s the most abundant element around you. “It’s madness, in one sense, having the Haber-Bosch process when what you’re doing is shipping nitrogen all around the world, when it’s literally all around us,” says Professor P. J. Cullen, from the University of Sydney’s School of Chemical and Biomolecular Engineering. Lightning naturally splits N2 and allows it to be “fixed” in soil and used by plants.Credit: Getty Images About 78 per cent of the air we breathe is composed of nitrogen. There’s about 81,000 tonnes of it hanging above every hectare on the planet. The trouble is most plants can’t use atmospheric nitrogen, or N2. The molecule has to be split and “fixed” into a compound with another element, such as a nitrate (NO3) or ammonia (NH3), before plants can take it up. This can happen naturally when the enormous power of lightning splits N2 and produces nitrates that rain down into soil. Cullen and his colleagues at startup PlasmaLeap harness miniature lightning strikes and plasma to produce nitrogen-based fertiliser themselves. Bottled lightning: a tube where bubbles are zapped to create plasma.Credit: PlasmaLeap Their process works by zapping air bubbles in water with renewable electricity, which excites the oxygen and nitrogen naturally in air to form the fourth state of matter, called plasma. “After a lightning storm you smell the air, you can smell the storm; the lightning strikes have basically split nitrogen and split oxygen”, which you can smell as ozone or nitrogen oxides, Cullen says. The mini man-made lightning zapping the bubbles achieves the same effect, splitting N2 and O2, which reform into NO3, a form of nitrogen plants can use. As a former farmer of beef and barley – otherwise known as steaks and beer – Cullen says the process could allow farmers to make their own fertiliser on site, slashing carbon emissions and transport costs associated with the Haber-Bosch process. “If you can electrify the process, it allows you to decentralise, and that gets rid of the need to ship or move the product itself.” Now, with a paper published in major chemistry journal Angewandte Chemie, Cullen and his University of Sydney colleagues have gone a step further. A new fuel for aircraft? Transforming air into ammonia is a bit of chemical holy grail. Most methods for producing “green ammonia” make the chemical in a liquid solution. But to really unlock ammonia’s potential, we need it in gaseous form, Cullen says. Ammonia could serve as a new fuel for aircraft that doesn’t produce carbon emissions when burned.Credit: Brook Mitchell “This is our ultimate goal, to go from atmospheric air and convert it into a gaseous product that could have many applications from agriculture to green ammonia as a fuel for the shipping industry.” Ammonia is a frontrunner candidate for carbon-free fuel; it produces nitrogen and water when burned. While batteries are greening cars and other land-based vehicles, long-haul ships, and aircraft need new fuel options because batteries are too heavy. Ammonia could also offer a more energy-efficient way to transport green hydrogen because it’s composed of one nitrogen atom and three hydrogen atoms. Nitrogen and oxygen are split from air via plasma before they’re passed through a silver electrolyser to form ammonia gas.Credit: PJ Cullen According to the CSIRO: “Renewable hydrogen could be converted to renewable ammonia and liquefied, then transported to where it is needed via trucks, trains and ships as we transport ammonia now. “Once it reaches its destination, it could be converted back into hydrogen and nitrogen, and the hydrogen could then be used in a hydrogen vehicle, or to make electricity, or as a fuel.” Cullen’s newly described process used the plasma method to split nitrogen and oxygen atoms from air, which are then passed into an electrolyser. This square silver device is where the magic happens: the gas passes through a membrane and a chemical catalyst and emerges as ammonia. “The two stage-process allowed us to use the plasma to do the heavy lifting in terms of being strong enough to split the strong nitrogen, and then we use the electrolyser to bond on the hydrogen,” Cullen says. The electrolyser needs to be made three times more energy efficient to become industrially competitive. But the transubstantiation of air into precious ammonia gas is a promising leap forward. “The Haber-Bosch was genius and won a Nobel Prize,” Cullen says. “But, fundamentally, it makes absolutely no sense to be dependent upon it.”