Feeding Plants with Electricity
Without the chemical element nitrogen (N), life as we know it would be impossible – nitrogen is an important component of amino acids and is thus essential for practically all living beings on our planet. In animals, and of course also in humans, amino acids are the basic building blocks of muscles, skin and other tissues. In plants, moreover, nitrogen is an important component of chlorophyll, which enables them to harvest energy through photosynthesis. The biosynthesis of all biologically important nitrogen-containing compounds depends on the supply of nitrogen species such as ammonia (NH3), since neither plants nor animals can absorb nitrogen directly from air (N2). Through symbiosis with certain bacteria, some plants (e.g. clover) have found a way, to fixate N2 from air in special root nodules as NH3, thus making it bioavailable.
In order to ensure a targeted supply of nitrogen in modern agriculture, the Haber-Bosch process was developed about 100 years ago, which allows the conversion of N2 from air into NH3. This process was a crucial factor in making our modern world possible, because without nitrogen fertiliser, only a fraction of the world's population could be fed today. The major disadvantage of the Haber-Bosch process is that the hydrogen used is obtained from fossil resources and that it requires an enormous amount of energy due to its reaction conditions. In order to make industrial ammonia production sustainable and CO2-neutral, research towards alternative approaches has been going on for years. Very often, these approaches have been based on the biological model, but have usually not been able to demonstrate the necessary efficiency.
In this project, a completely different approach is to be taken. The aim is to combine a special form of solid oxide electrolysis cells with novel electro-catalysts in order to fixate nitrogen from the air with renewable electricity as ammonia. The special feature of this type of electrolysis cells is that they can provide extremely high hydrogen pressure locally at one of the electrodes, by applying an electrical voltage. This can be used to directly hydrogenate N2 thus obtaining NH3. The prerequisite for this is the combination of the cell’s hydrogen electrode with certain catalysts that make it possible to bind N2 from the air and to split its very stable chemical bond. The particular challenge here arises from the complex interactions of the individual materials, which need to be combined and matched in such a way that the desired functionality is obtained with sufficient efficiency. If the endeavour succeeds, it will be possible in the future to convert green electricity with atmospheric nitrogen into plant fertiliser, which can thus be used decentrally all over the world for sustainable food production.