Hydrogen adsorption/desorption properties of mechanically milled activated carbon

We investigated the hydrogen adsorption/desorption properties of activated carbon that was prepared by mechanical milling in a hydrogen atmosphere at an ambient temperature. Although the hydrogen concentration estimated by inert gas fusion-thermal conductivity method increased with milling time up to 10 h, samples milled for longer than 10 h showed little dependence on milling time. Ultimately, the hydrogen concentration reached about 2.6 wt.%. Thermal desorption mass spectroscopy (TDS) revealed that the desorption spectrum of the hydrogen molecules (mass number=2) in a sample milled for 10 h contained peaks at about 500 and 800 degreesC. The desorption activation energies of hydrogenated activated carbon at these temperatures were calculated to be 124 and 237 kJ/mol, respectively. These values suggest that the hydrogen in activated carbon probably exists as hydrogen molecules and atoms. The mechanism of hydrogen adsorption by activated carbon may consist of hydrogen adsorption into the pores in the carbon in the form of hydrogen molecules, and a combination of dangling bonds created by mechanical milling, with hydrogen atoms. (C) 2003 Elsevier B.V. All rights reserved.