Evaluation of the physi- and chemisorption of hydrogen in alkali (Na, Li) doped fullerenes

• Physisorption properties of Li and Na doped C60 were investigated for the first time.
• The first mass spectrometric evidence for the existence of C60H60 is presented.
• Alkali doped fullerenes were synthesized by two methods and compared.
• Increased isosteric heats of adsorption for lithium doped fullerenes are presented.
• The hydrogen storage properties of C60 are enhanced by both alkali doping methods.

In this study, alkali doped fullerenes synthesized by two different solvent assisted mixing techniques are compared for their hydrogen uptake activity. In particular, we investigated the interaction of hydrogen with lithium and sodium doped fullerenes via physisorption. In addition, we present the first mass spectrometric evidence for the formation of C60H60 via chemisorption. Hydrogen physisorption isotherms up to 1 atm at temperatures ranging from 77 K to 303 K were measured demonstrating an increase in hydrogen uptake versus pure C60 and increased isosteric heats of adsorption for the lithium doped fullerene Li12C60. The hydrogen uptake in Na6C60, Li6C60, and Li12C60 was enhanced compared to pure C60. However, despite these improvements the low amount of physisorbed hydrogen at 1 atm and 77 K in these materials suggests that fullerenes do not possess enough accessible surface area to effectively store hydrogen due to their close packed crystalline nature.