Carbon nanocomposites synthesized by high-energy mechanical milling of graphite and magnesium for hydrogen storage

Nanocomposites obtained by mechanical milling of graphite and magnesium with organic additives (benzene, cyclohexene or cyclohexane) have been studied with the aim of preparing novel hydrogen storage materials. The organic additives were very important in the milling processes to determine the characteristics of the resulting carbon nanocomposites. The mechanical milling with high energy resulted in the generation of large amounts of dangling carbon bonds in graphite with simultaneous decomposition of graphite structure. Such dangling bonds of carbon acted as sites to take up hydrogen. It has been proved by temperature programmed desorption (TPD) and neutron diffraction measurements that the hydrogen taken up in the nanocomposites exists in at least two states; in the form of C-H bond formation in the graphite component and in the form of hydride in the magnesium component. The relative amounts of two types of hydrogen strongly depended upon differences in additives used (benzene, cyclohexene or cyclohexane). When C6D6 besides C6H6 was used as additive, the hydrogen taken up was discussed from the standpoint of isotope effects. Upon addition of titanium tetraisopropoxide, the features of hydrogen uptake by the nanocomposites changed completely. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.