Sergey Macheret and Andrey Starikovskiy of US Plasma Engineering LLC discuss breakthrough plasma technology for nitrogen fixation and the production of sustainable fertilisers.
Electrification of chemistry
Electrification has become a central strategy for decarbonisation and sustainability across many sectors of the global economy. The transportation sector is transitioning from internal combustion engines to electric vehicles.
Industrial heating, which has traditionally relied on coal and natural gas, is being replaced by electric furnaces, heat pumps, and induction technologies. The chemical industry – the backbone of modern manufacturing – has begun a similar transformation: the electrification of chemistry. This concept involves designing and operating chemical processes that use electricity as the primary energy source, replacing fossil fuel combustion as a source of both heat and hydrogen.1
Electrification offers many benefits. When powered by renewable sources such as wind or solar energy, electric processes can be nearly carbon-free. They also enable decentralised production, allowing for smaller, modular facilities closer to end-users, which could reduce transport costs and supply chain vulnerabilities. Water electrolysis powered by renewable energy, for instance, produces “green hydrogen,” an increasingly recognised cornerstone for low-carbon ammonia, methanol, and synthetic fuels.2 High-temperature electrolysis and plasma-assisted reactors can supply heat or reactive intermediates without burning hydrocarbons. Another example is the electrochemical reduction of CO₂ to produce fuels and chemicals.3, 4
The urgency of this transition stems from the large carbon footprint of the chemical industry. About 7% of global greenhouse gas emissions come directly from chemical manufacturing.5 Achieving net-zero targets by mid-century will require alternatives to traditional energy-intensive processes such as steam methane reforming, ethylene cracking, and Haber-Bosch ammonia synthesis.
Electrified approaches – especially those that can operate flexibly and intermittently with variable renewable electricity – are an active area of research and investment. Large companies such as BASF, Air Liquide, and Siemens Energy have announced projects to develop electrochemical or plasma-based synthesis routes for ammonia and other chemicals.6
Plasma technologies for electrification of chemistry
Among the most promising electrification tools are low-temperature plasmas, which are weakly ionised gases where electrons are much hotter than the bulk gas. The electron temperature can reach several electron-volts, or tens of thousands of Kelvin, while the gas can remain near room temperature or be moderately heated.7 This unique property allows plasmas to drive chemical reactions without heating the entire gas volume to the high temperatures required for thermal chemistry.8
In a low-temperature plasma, energetic electrons collide with neutral molecules, either dissociating or exciting them to higher electronic or vibrational states. These excited species – radicals, ions, and metastable molecules – are chemically reactive and can initiate and sustain reactions that would otherwise require high thermal input.8
In addition to electron impact reactions, ions in the plasma can bombard surfaces, thereby enhancing surface chemistry. This process forms the basis for plasma etching and deposition in semiconductor fabrication, an indispensable process for producing microchips with nanometre-scale features.9
In principle, plasmas could match or surpass the performance of thermal catalytic methods for bulk chemical processes. 8, 10
However, energy efficiency is the critical hurdle. Energy-intensive processes, such as CO2 reduction and nitrogen fixation, require the plasma process to consume no more (or at least not much more) energy per unit amount of product than existing thermal technologies. Otherwise, they will not be economically or environmentally competitive. Therefore, the key metric is the specific energy cost (e.g., in megajoules per mole of nitrogen fixed or per kilogram of product).
Another problem is that, to be practical, the plasma chemical process must operate at atmospheric or near-atmospheric pressure. In contrast to low-pressure plasmas, which can be easily sustained in nonequilibrium and are uniform and tunable for optimal performance, as in plasma systems for microchip fabrication, atmospheric-pressure plasmas are more challenging to control. They easily break into narrow channels that often become hot, thermally-equilibrium arcs.7
Several approaches have been explored to improve plasma efficiency, including nanosecond pulsed discharges to enable nonequilibrium while minimising gas heating; gliding arcs or microwave plasmas; and catalytic surfaces integrated with plasmas to enhance reaction pathways.8, 11 Yet, despite decades of research, achieving energy costs comparable to those of mature thermal chemical processes remains challenging.
Nitrogen fixation and production of nitric acid and fertilisers
Nitrogen is a vital element in biology and industry. Compounds containing nitrogen are essential for agriculture (fertilisers like ammonium nitrate and urea), pharmaceuticals, dyes, polymers, and even explosives and rocket propellants.
However, atmospheric nitrogen exists as N₂, a molecule held together by one of the strongest chemical bonds: a triple bond with a dissociation energy of 941 kJ/mol.12 Nitrogen fixation is the conversion of N₂ into reactive forms such as ammonia (NH₃) or nitric oxide (NO). This process is inherently energy-intensive.
In nature, living organisms fix nitrogen via enzymes called nitrogenases. However, at an industrial scale, humans rely on the Haber–Bosch process, which involves reacting nitrogen with hydrogen at temperatures between 400 and 500 °C and pressures between 150 and 250 bar over iron-based catalysts to form ammonia (NH₃). The hydrogen feedstock is typically derived from natural gas via steam methane reforming, a process that releases significant amounts of CO₂. The Ostwald process then oxidises the ammonia into nitric oxide (NO) using platinum-rhodium catalysts at approximately 850°C and moderate pressure. This is followed by further oxidation and absorption in water to produce nitric acid (HNO₃).
This combined technology, developed in the early 20th century, revolutionised agriculture. Synthetic fertilisers dramatically increased global crop yields and supported the food supply for billions of people.13 Today, the Haber-Bosch–Ostwald process produces over 170 million tonnes of ammonia annually and underpins nearly all commercial nitric acid production.14
However, the process is resource- and emission-intensive. Estimates suggest that the Haber-Bosch process accounts for approximately 1–2% of global energy consumption and generates 1-3% of global CO₂ emissions.15 The process is also capital-intensive in terms of the capital cost per unit amount of product manufactured annually. Furthermore, small-scale plants would have an even higher capital cost per unit amount of product, making them economically non-viable. Large-scale Haber-Bosch plants are economically viable only when co-located with natural gas sources to minimise hydrogen costs. These constraints create vulnerabilities in fertiliser supply and lead to price volatility. As global efforts to decarbonise intensify, researchers and industry professionals are seeking sustainable, decentralised alternatives with low capital costs.
Plasma-based approaches to nitrogen fixation
Interest in plasma-based nitrogen fixation is not a new phenomenon. Before Haber-Bosch, in the early 1900s, Birkeland and Eyde developed an electric arc process for NO synthesis using hydroelectric power in Norway. 16 Although effective, this process was far less energy-efficient than the Haber-Bosch process and was abandoned once cheap natural gas became available. Modern plasma research has revived these ideas, but now with advanced reactors, power electronics, and the prospect of abundant renewable electricity. There is also a much deeper understanding of the mechanisms of processes in weakly ionised air and air-water plasmas,17 from vibrational excitation8, 18 to the processes at the plasma-liquid interface.17, 19
Several research groups have explored direct ammonia synthesis from N₂ and H₂ or N₂ and H₂O via microwave, dielectric barrier, or gliding arc discharges. Although ammonia yields have improved, energy costs often exceeding 10–20 MJ/mol N remain far above the Haber-Bosch benchmark of ~0.5–0.6 MJ/mol N when considering the full process.20 Similarly, direct plasma oxidation of air to nitric oxide (NO) or nitric acid has been extensively investigated. The advantage is that no hydrogen feedstock is needed, just air and electricity, which could enable small, modular fertiliser plants powered by renewable energy. However, until recently, the energy cost remained a challenge.
Energy efficiency benchmark and recent performance data
Techno-economic analyses quantify the challenge. A 2023 study21 calculated that for a plasma process to compete in nitric acid production, its specific energy cost must not exceed 1–1.5 MJ/mol N, a benchmark that includes the cost of renewable electricity and downstream handling.
For comparison, gliding arc reactors and microwave plasmas have produced nitric oxide (NO) at atmospheric pressure, with typical energy costs of 2–5 MJ/mol N.22 The most successful atmospheric-pressure plasma experiments to date – NO production in a gliding arc discharge with a special nozzle exhaust23 – have achieved only 2.1 MJ/mol N when ideal downstream oxidation and absorption are assumed.
Researchers have also studied plasma-liquid systems, in which NOₓ species formed in the plasma dissolve directly into water, forming nitric acid or nitrates. However, overall energy expenditures are higher due to losses in mass transfer and secondary reactions. The best published result24 among studies where the final product was nitric acid or aqueous nitrate is 13.9 MJ/mol N, which is an order of magnitude higher than what is required21. Other published studies in which liquid nitrate was produced had even higher energy costs, up to hundreds of MJ/mol N.24
These numbers highlight why plasma methods have not yet disrupted the Haber-Bosch-Ostwald technology. Without a breakthrough in energy efficiency, plasma nitric acid production cannot compete with conventional processes on either an economic or environmental basis.
Both researchers and investors recognise that any technology achieving ≤1 MJ/mol N under practical conditions would be transformative, allowing clean, flexible, and distributed fertiliser production without the use of fossil fuels. This would decarbonise a major industrial sector and enhance food security and supply resilience worldwide.
The groundbreaking development in plasma-based nitrogen fixation
US Plasma Engineering LLC (USPE) has been working for some time on the plasma fixation of nitrogen, using only air and water to form a liquid nitrate (nitric acid). We focus on advanced modern techniques to control and manipulate plasmas at atmospheric pressure25 to engineer an optimal plasma chemical reactor.
To this end, we have developed a novel plasma chemical reactor and built a laboratory-scale prototype. Experiments with this prototype have validated the concept. Using standard methods to measure power deposition into the plasma and the concentration of the product (aqueous NO₃⁻), we achieved an energy cost of 0.54 MJ/mol N. To the best of our knowledge, this represents the lowest energy cost achieved with atmospheric-pressure plasma technology. It certainly satisfies the stringent energy cost requirement for a plasma process to be competitive. The reactor has not been fully optimised yet, and further reduction in the energy consumption per unit amount of product is possible.
This breakthrough in the energy efficiency of plasma nitrogen fixation opens new horizons for the chemical industry and agriculture. When scaled up, this novel, electrically powered plasma-based process can produce nitric acid and nitrogen fertilisers from air and water. This avoids the use of hydrocarbon feedstock and CO₂ emissions. Compared to traditional chemical processes, plasma-based technology is expected to be significantly less capital-intensive.
In fact, estimates indicate that the capital cost of a plasma facility per unit amount of nitrogen fixed annually is 4 to 6 times lower than that of the Haber-Bosch-Ostwald process. Furthermore, plasma technology is modular and can be easily scaled up or down. Small production plants are as economically efficient as large ones, which contrasts sharply with Haber-Bosch technology, which is economically viable only on a very large scale.
The estimated production costs with the new plasma technology can be quite low, and some savings could be passed on to farmers.
Breakthrough plasma technology enables sustainable, flexible production in small, local, or regional plants with low energy costs. This technology will transform the way fertilisers are made and used by replacing the current fossil fuel-based, highly centralised production process with its associated long-distance transport and geopolitical price volatility.
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Sergey Macheret
Chief Technology Officer
+1 (609) 731-6865
usplasmaeng@yahoo.com
https://usplasmaengineering.com/
Andrey Starikovskiy
Chief Scientist
+1 (215) 422-2703
usplasmaeng@yahoo.com
https://usplasmaengineering.com/
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