​There is renewed interest in intercalated fullerides in the field of energy storage, due to their performance as hydrogen-absorbing materials. An international team of researchers investigated sodium (Na) and lithium (Li) doping of Buckminster fullerene (C₆₀). In general, sodium-doped C₆₀ compounds have release hydrogen at a lower temperature. However, lithium-doped C₆₀ compounds are lighter and can absorb larger quantities of hydrogen. In this work, the group investigated adding small amounts of sodium into a mainly lithium-doped C₆₀ compound with the aim of balancing these benefits.

After characterisation of the structure of the mixed fullerides using X-ray powder diffraction and Raman spectroscopy, the group measured their hydrogen uptake and release. They found that the temperature of hydrogen release decreased as the amount of sodium was increased. The researchers then used muon spin relaxation experiments on EMU to compare Na_xLi_6-xC₆₀ and Na_xLi_12-xC₆₀ compounds. They found that, for Na_xLi_6-xC₆₀, the muonium has a preference for binding to the outside of the fullerene molecule, whereas for Na_xLi_12-xC₆₀ (the fulleride with the higher lithium content) the muonium preferentially binds with the lithium atom. This is likely to lead to the formation of LiH, which will reduce the rate of hydrogen adsorption, explaining the improved properties of Na_xLi_6-xC₆₀ when sodium is added to replace lithium.

Related publication: “Synthesis and characterization of mixed sodium and lithium fullerides for hydrogen storage" International Journal of Hydrogen Energy, Volume 43, Issue 34, Pages 16766-16773, DOI: 10.1016/j.ijhydene.2018.03.210

Authors: Mattia Gaboardi (ISIS), Nicola Sarzi Amadè (Universitá di Parma), Mauro Riccò (Universitá di Parma), Chiara Milanese (Universitá Degli Studi di Pavia), Alessandro Girella (Universitá Degli Studi di Pavia), Marta Gioventù (Universitá Degli Studi di Pavia), and Felix Fernandez-Alonso (ISIS; University College London).

Instrument: EMU