Hydrogen adsorption properties of activated carbons with modified surfaces

The hydrogen adsorption isotherms of activated carbon fibers loaded with platinum (Pt-ACF) and palladium (Pd-ACF) were accurately measured at ambient temperature over the hydrogen pressure range 0-3.5 MPa by using a high-pressure adsorption apparatus. The amounts of hydrogen adsorbed on the Pt-ACF and Pd-ACF samples were larger than the amount adsorbed on the unmodified ACF sample. Detailed measurement of the hydrogen adsorption isotherms of Pt-ACF and Pd-ACF at a hydrogen pressure up to 0.1 MPa indicated that the increase in adsorption was due to chemisorption of hydrogen on the metal. The hydrogen adsorption properties of ACF oxidized with (NH(4))S(2)O(8) or reduced in a hydrogen flow at 1073 K were evaluated at 77 and 303 K over the hydrogen pressure range 0-3.5 MPa. The amount of adsorbed hydrogen was decreased by oxidation and increased by reduction. This result is attributable to a change in the pore structure: that is, oxygen functional groups introduced on the carbon surface inhibited hydrogen adsorption into the micropore with an optimum pore diameter. (C) 2004 Elsevier B.V. All rights reserved.