The Haber process currently helps feed more than half the world, producing 150m tonnes of ammonia a year. This is forecast to rise further, in line with the food demand of a growing world population.
And yet, it has serious drawbacks. In its traditional form, the process requires high temperatures – around 500°C – to make the extremely stable molecule nitrogen reactive.
The Haber process takes place at extremely high temperatures, similar to that of an average fire.
It also needs high pressure to shift the equilibrium towards the desired product. The process is sensitive to oxygen, meaning that nitrogen and hydrogen must be introduced as purified elements, rather than as air and water.
These requirements together make the process extremely energy-hungry; estimated to consume between 1% and 2% of global primary energy production. In 2010, the ammonia industry emitted 245m tonnes of CO2 globally, corresponding to half the UK’s emissions.
The Haber process was developed by Carl Bosch (left) and Fritz Haber (right) in the early 20th century. Image: Wikimedia Commons
In nature, the process relies on the highly complex enzyme nitrogenase, operating at an ambient pressure and temperature. But using the entire biological system would not be economical for large-scale industrial synthesis, and thus the search for an inorganic system that matches the performance of the biological has become an important challenge.
In recent years, novel electrochemical approaches and new catalysts have yielded promising results suggesting that, at least for small-scale synthesis, other ways may have a future.
The chemical reaction that feeds the world. Video: TED-Ed
‘The last [few] years brought some spectacular results on ammonia synthesis research,’ comments Hans Fredriksson from Syngaschem at Eindhoven, Netherlands.
‘On the catalyst side, there is the discovery of ‘super promoters’, helping N2 dissociation, allowing lower process temperatures, while optimised catalyst formulations yield significant improvements in activity.
‘Perhaps even more exciting are new approaches in processing, for example by electrochemistry, or simply running the reaction in an electric field, or bringing plasmas into play,’ he said.
In 2013, Shanwen Tao, then at the University of Strathclyde, Glasgow, UK, and colleagues demonstrated for the first time the production of ammonia from air and water, at ambient temperature and pressure, using a proton-conducting Nafion membrane in an electrochemical approach.
Nafion, a Teflon-like material that conducts cations but neither electrons nor anions, is also used in fuel cells.
‘Electrochemical synthesis of ammonia is an important new approach for efficient synthesis of ammonia using green renewable electricity as the energy source. This could be a key technology for a possible ‘ammonia economy’,’ where ammonia replaces or complements hydrogen as an energy carrier, says Tao.
Researchers hope new approaches will be supported by renewable energy, reducing CO2 emissions. Image: Pexels
Separate efforts using different routes are being developed in Japan, with a particular focus on ruthenium as an efficient catalyst. One approach is to apply super promoters to provide electrons that destabilise nitrogen by weakening the triple bond and making the molecule more reactive for ammonia synthesis.
This was first reported in 2012 by Hideo Hosono’s group at the Tokyo Institute of Technology, who used ruthenium catalysts in combination with ‘electrides’ – a new class of ionic materials where electrons serve as the anions.
The method operates at atmospheric pressure and temperatures between 250 and 400°C, and hydrogen poisoning of ruthenium catalysts is no longer a problem.
Ruthenium is a type of metal in the platinum group. Image: Metalle-w/ Wikimedia Commons
‘This catalyst exhibits the highest activity and excellent long-term stability,’ says Hosono, who sees the future of his methods in distributed, small-scale applications of ammonia synthesis.
Hans Niemantsverdriet, director of SynCat@Beijing, China, acknowledges the rapid progress being made, but also strikes a note of caution.
‘In spite of interesting discoveries, I find it hard to imagine that these improvements will be able to replace the current large-scale and fully optimised technology,’ he says. ‘In the fertiliser area, novel technology will at best become a niche market for very special situations. Also, the CO2 footprint is hardly diminished.’
Ammonia is a core component of fertiliser, feeding nitrogen to plants for photosynthesis. Image: Maurice van Bruggen/Wikimedia Commons
In the long term, Niemantsverdriet has hope for the ammonia economy as championed by Tao and others, providing carbon-free hydrogen from renewable energies.
‘I strongly believe that there will be scope for large industrial parks where this technology can be cleverly integrated with gasification of coal in China, and perhaps biomass elsewhere,’ he says. ‘If dimensioned properly, this has the potential to reduce the carbon footprint in the future.’
Energy storage is absolutely crucial in today’s world. More than just the batteries in our remote controls, more even than our mobile phones and laptops; advancements in energy storage could solve the issues with renewable power, preserving energy generated at times of low demand.
Advances in lithium-ion batteries have dominated the headlines in this area of late, but a variety of developments across the field of electrode materials could become game changers.
1. In the beginning, there were metals
The Daniell cell, an early battery from 1836 using a zinc electrode. Image: Daderot
Early batteries used metallic electrodes, such as zinc, iron, platinum, and lead. The Daniell cell, invented by British chemist John Frederic Daniell and the historical basis for the volt measurement, used a zinc electrode just like the early batteries produced by scientists such as Alessandro Volta and William Cruickshank.
Alterations elsewhere in the Daniell cell substantially improved its performance compared with existing battery technology and it became the industry standard.
2. From acid to alkaline
Waldemar Jungner: the Swedish scientist who developed the first Nickel-Cadmium battery. Image: Svenska dagbladets årsbok 1924
Another major development in electrode materials came with the first alkaline battery, developed by Waldemar Jungner using nickel (Ni) and cadmium (Cd). Jungner had experimented with iron instead of cadmium but found it considerably less successful.
The Ni–Cd battery had far greater energy density than the other rechargeable batteries at the time, although it was also considerably more expensive.
3. Smaller, lighter, better, faster
Organic materials for microbattery electrodes are tested on coin cells. Image: Mikko Raskinen
Want your electronic devices to be even smaller and lighter? Researchers from Aalto University, Finland, are working on improving the efficiency of microbatteries by fabricating electrochemically active organic lithium electrode thin films.
The team use lithium terephthalate, a recently found anode material for a lithium-ion battery, and prepare it with a combined atomic/molecular layer deposition technique.
4. There’s more to life than lithium
50-70% of the world’s known lithium reserves are in Salar de Uyuni, Bolivia. Image: Anouchka Unel
Lithium-ion batteries have dominated the rechargeable market since their emergence in the 1990′s. However, the rarity of material means that, increasingly, research and development is focused elsewhere.
Researchers at Stanford University, USA, believe they have created a sodium ion battery with the same storage capacity as lithium but at 80% less cost. The battery uses sodium salt for the cathode and phosphorous for the anode.
5. Back to the start
Advances are also being made in the electrode materials used in artificial photosynthesis. Video: TEDx Talks
Hematite and other cheap, plentiful metals are being used to create photocatalytic electrode materials by a team of scientists from Tianjin University, China. The approach, that combines nanotechnology with chemical doping, can produce a photocurrent more than five times higher than current approaches to artificial photosynthesis.
You can read an interview with the recipient of SCI’s 2017 Castner Medal, who delivered the lecture Developments in Electrodes and Electrochemical Cell Design, here.