It Works! Significantly Higher Ammonia Yield Due to Magnetic Field Influence

Researchers from Berlin (Germany) have discovered how the synthesis of ammonia can be made significantly more productive using a magnetic field ...

Ammonia is needed in everything from the hydrogen economy to the production of fertilizers. However, the key to greater sustainability and efficiency is new catalysts for the production of ammonia. Ammonia synthesis using the well-known Haber-Bosch process, for example, requires between one and two percent of the world's energy. However, according to the Helmholtz-Zentrum Berlin, this energy-intensive process is no longer without competition. This is because a newer approach is based on the electrochemical conversion of nitrate into ammonia. Nitrate is found, for example, in liquid manure, which is produced in large quantities in intensive agriculture and can be particularly harmful to water bodies. However, suitable catalysts would have to suppress the development of hydrogen and nitrogenous by-products during the conversion of nitrate to ammonia. However, the class of materials known as spinel transition metal oxides is considered particularly promising for this—especially thin films of the material CoFe₂O₄, a cobalt-iron oxide. And if an external magnetic field is applied to the system that carries out the catalysis, the efficiency and selectivity can be increased enormously, according to the report from Berlin.

The Effectiveness of the Magnetic Field Has Been Impressively Demonstrated

The CoFe₂O₄ layers that were produced under a magnetic field of one tesla strength worked best, they say. Compared to CoFe₂O₄ without the influence of a magnetic field, three times the amount of ammonia was produced, as the researchers emphasize. If you compare the ammonia yield of the CoFe₂O₄ catalyst under the influence of a magnetic field with that of pure iron oxide Fe₃O₄, which was also synthesized at a magnetic field of one Tesla, it is even many times higher (22×). This proves that cobalt plays a decisive role in nitrate reduction. Supplementary DFT calculations prove that cobalt actually suppresses the competing hydrogen evolution and at the same time promotes nitrate conversion. The applied magnetic field therefore stabilizes the catalytically active Co²⁺ ions at octahedral sites, which obviously lowers the kinetic barriers for nitrate reduction.

The Stronger the Magnetic Field, the Rougher the Surface

This means that, in addition to temperature and pressure, a magnetic field is also an effective parameter for controlling the cation distribution, magnetic domains and surface states during the growth of thin films of CoFe₂O₄. Although the magnetic field is only applied during thin-film growth, the improvements have a lasting effect afterwards, even in field-free electrochemical operation, as the Berliners were able to determine. This makes the new approach particularly promising for practical applications, as no external magnetic field is required during electrolysis. Scanning electron microscope images (see image) show that the surfaces of the thin films systematically become rougher—and therefore larger—the stronger the magnetic field was during synthesis. It is now hoped that these results will stimulate broader research into magnetic field-assisted strategies for the customized production of electrocatalysts.