Material concept makes hydrogen refuelling easier and faster
Hydrogen could offer a perfect solution for CO2-neutral mobility, at least if the gas is generated by electricity from wind power. However, one of the limiting factors for the use of hydrogen is the lack of an efficient storage system. In today’s fuel cell cars, hydrogen is filled into compressed gas tanks at pressures of up to 700 bar. This solution is expensive and technically demanding. A promising alternative is solid fuel storage systems based on magnesium-nitrogen.
Magnesium hydrides as storage media for hydrogen have been researched at the Helmholtz Zentrum Geesthacht (Germany) for several years. The advantage over conventional pressure tanks is that they store more hydrogen and thus more energy for the same volume. As an example, a fuel cell car can travel about 500 km with 5 kilograms of hydrogen. For five kilograms of hydrogen, a high-pressure tank requires a volume of 122 litres, while a tank based on magnesium hydride requires a volume of only 46 litres. However, there is also a drawback: high temperatures of around 300°C are required for refueling.
To reduce this temperature, the researchers add additives such as nitrogen. This, however, reduces in turn the absorption capacity of the system. The scientists at the Helmholtz Centre in Geesthacht therefore developed a hydride composite system that should be able to be refueled very quickly at relatively low working temperatures of below 180°C.
Conventionally, the refueling process for the magnesium-nitrogen-based hydride systems takes around 30 minutes for 5 kilograms of hydrogen. The HZG scientists have now succeeded in combining two additives that drastically accelerate the refueling process: The element potassium and lithium titanate oxide. For this purpose, the scientists have ground potassium and titanate together with the magnesium-nitrogen system into tiny nanoparticles. This enlarges the surface area of the individual particles, causing them to bind more hydrogen.
HZG doctoral student Gökhan Gizer conducted countless experiments for the study. He has now achieved a breakthrough: In his recently published study, the materials researchers were able to show that potassium-lithium-titanate nanoparticles as catalysts accelerate the loading of hydrogen in the magnesium-nitrogen system. “We have thus invented a system that makes the refueling process about five times faster than without potassium lithium titanate,” explains Gizer.
The scientists are now working on the goal of optimizing the reaction kinetics of these new materials and qualifying them for technical use in vehicles.
More information: https://www.hzg.de/index.php.en
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