NitroVolt (formerly Nitrofix Solutions), a Denmark cleantech startup founded in 2022, develops a distributed ammonia synthesis unit that uses nitrogen gas, hydrogen, and renewable energy to make green ammonia through electrochemical processes. NitroVolt aims to decarbonize nitrogen-based fertilizer production one farm at a time. This lowers the costs of transporting fertilizer and makes the agricultural industry more sustainable.
Challenges: green ammonia
Ammonia (NH₃) is a crucial compound for agriculture. In 2021, the global production of ammonia was 185 million metric tons, with over 80% being used for fertilizer production. As the global population increases, so does the demand for ammonia.
However, ammonia production consumes about 2% of worldwide fossil fuel due to the energy-intensive nature of the process. This generates over 420 million tons of carbon dioxide (CO₂) annually, which accounts for 1.5% of global greenhouse gas emissions.
The primary method of ammonia production is the Haber-Bosch process carried out in a large industrial plant. The Haber-Bosch process converts hydrogen (H₂) and nitrogen (N₂) into ammonia. This process requires extreme reaction conditions involving high pressure (150 – 350 atm) and temperature (400 – 550 ºC), along with pure hydrogen, usually obtained from the steam reforming process of natural gas.
Therefore, there is an urgent need to develop technologies for ammonia synthesis in a sustainable manner. The utilization of renewable energy to convert N₂ and green hydrogen into NH₃ represents a promising approach for the production of green ammonia production.
NitroVolt has developed a continuous-flow electrolyzer for ammonia electrosynthesis based on lithium-mediated electrochemical nitrogen reduction reaction (Li-NRR). This process involves the reduction of lithium salt to metallic lithium. This metallic lithium then reacts with nitrogen to form a lithium nitride. The lithium nitride is easily protonated by hydrogen from hydrogen gas oxidation, leading to the formation of ammonia. The lithium is then released back into the solution, ready to start the process over again.
NitroVolt’s key technology is the continuous-flow electrosynthesis of ammonia. Its continuous-flow electrolyzer operates under a constant stream of reactants, which promotes efficient mass transfer and creates products continuously. This method can achieve a Faradaic efficiency for ammonia production of up to 61% and an energy efficiency of 13% under ambient temperature and pressure. In comparison to the electrosynthesis of ammonia in batch reactors, this continuous-flow approach is easy to scale up.
The diagram below depicts the system of the continuous-flow electrosynthesis of ammonia.
The system comprises a continuous-flow electrolyzer coupled with an electrolyte tank, reactant tanks of nitrogen and hydrogen gasses, a hydrogen trap, and an acid trap.
The electrolyte flows through an electrolyte chamber of the electrolyzer. The electrolyte solution consists of 1.0 M lithium tetrafluoroborate (LiBF₄) in 99 vol.% anhydrous tetrahydrofuran and 1 vol.% ethanol. The reactant gas streams flow at a pressure of 1 bar through the electrodes via their gas flow field channels. The acid trap solution is hydrochloride (HCl) solution.
Prior to flowing the electrolyte into the electrolyzer chamber, the purified nitrogen and hydrogen are introduced into the empty electrolyzer flow cell for at least 30 min. Afterward, the electrolyte solution is injected into the cell in nitrogen and hydrogen at atmospheric temperature and pressure, and a suitable potential is applied between the anode and cathode. The produced ammonia is trapped in the hydrochloride solution, forming ammonia hydrochloride (NH₄Cl). Some ammonia are trapped in electrolyte solution.
The diagram below illustrates the structure and operational mechanism of the continuous-flow electrolyzer.
The anode and cathode are separated by the electrolyte chamber. Both electrodes are made of stainless-steel cloth coated with platinum/gold (Pt/Au) alloy catalyst. The stainless-steel cloth serves as the gas diffusion layer, which is attached to the gas flow fields with patterned gas flow channels. The gas flow fields are attached to the current collectors.
During operation, lithium ions (Li⁺) diffuses from the bulk electrolyte through the solid-electrolyte interphase. They are electrochemically reduced into metallic lithium on the cathode. The metallic lithium subsequently reacts with N₂ which diffuses from the gas flow field channels to the cathode, forming lithium nitride (Li₃N). The lithium nitride is protonated by a proton (H⁺) shuttle of ethanol (EtOH) to continuously release ammonia (NH₃). The sustainable source of protons is provided by hydrogen oxidation on the anode.
The continuous-flow electrolyzer with a 25 cm² effective area achieves a Faradaic efficiency of up to 61% and an energy efficiency of 13% for ammonia production at a current density of 6 mA/cm² at ambient pressure and temperature. The use of Pt/Au alloy catalyst enhances the stability of the lithium-mediated electrochemical nitrogen reduction reaction system in the continuous-flow electrolyzer. The Faradaic efficiency can be stable for 10 hours.
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NitroVolt Technology Applications
Green ammonia can be used as a carbon-neutral fertilizer, significantly reducing the carbon footprint of farming. Using green ammonia for fertilizer could drive down farming’s carbon footprint by as much as 90% for corn and small grain crops.
Green ammonia can be used as a transport fuel, replacing highly polluting gasoline, diesel, and propane to run engines, generators, and turbines. It has applications in transportation including heavy goods vehicles, trains, aviation, and shipping.
Green ammonia has the potential to be used for large-scale, long-term energy storage. It has nine times the energy density of Li-ion batteries, and three times that of compressed hydrogen, making it a competitive option against electrochemical batteries, pumped hydro, and capacitors to balance consumption and renewable generation. Countries including Japan, Australia, the Netherlands, and the United Kingdom have national plans to use green ammonia to store (and export) their renewable energy surpluses.
NitroVolt’s technology is made to be housed in container-sized units that can be put right where they are needed, like on a farm or in a greenhouse, to make ammonia when it is needed. This unit the size of a container is meant to be decentralized and expandable. To make ammonia, the final system only needs air, water, and green electricity.
Jupiter Ionics has raised a total of $500K in funding over an Accelerator/Incubator on Oct 1, 2022.
NitroVolt is funded by The VILLUM P2X Accelerator.
Suzanne Zamany Andersen is CEO.