A new recipe for storing hydrogen involves taking magnesium diboride, putting it in a container, adding some hydrogen and ball bearings, and shaking vigorously. Unlike other methods, heating the mixture is not required. Creating a room-temperature-stable, solid-stored hydrogen fuel has been described as one of the grand challenges of science. MgB2 (previously known primarily for its high-temperature superconductivity) has a hexagonal structure of boron sheets separated by layers of Mg. High-energy reactive ball milling breaks down this structure, creates trapping sites for hydrogen, and forms boron-hydrogen bonds. Hydrogen uptake is relatively easy, as is its release and regeneration of the starting material. Hydrogen is released by heating above 200 °C; complete release is achieved by 390 °C. Using x-ray diffraction and solid-state nuclear magnetic resonance (the equivalent of a MRI machine) researchers were able to understand the unusual mechanism for hydrogen uptake by MgB2 and release from the borohydride material prepared by reactive milling. The formation of nanoscale particles during milling appears critical to the reversibility of the hydrogen uptake since stable intermediates no longer form during the release process. The results have important implications for the design of room temperature hydrogen storage devices and hydrogen-fueled machines of all types.
Facile Synthesis and Regeneration of Mg(BH4)2 by High Energy Ball Milling of MgB2