Effect of Pd on the hydrogen adsorption capacity of activated carbon fibers

First-principles calculations at Oak Ridge National Laboratory (ORNL) on interactions between hydrogen and graphite provided the fundamental basis for experimental work on metal-doped, activated carbon fibers (produced at Clemson University). Measurements at ORNL revealed that the Pd doped fibers exhibited a hydrogen storage capacity of about 2 wt% at ambient temperature and a pressure of 2 MPa, corresponding to a H/Pd atomic ratio of about 50:1. This represented an order of magnitude increase over the hydrogen storage capacity of the corresponding Pd free carbon fibers under similar conditions. Further modeling work indicated that, provided the high energy barrier for initial sorption could be overcome, hydrogen could be stored by intercalation between graphene layers. On the basis of these preliminary findings, it is hypothesized that metal assisted hydrogen storage in nanostructured carbon is the result of catalytic activation (dissociation) of molecular hydrogen and surface diffusion of hydrogen atoms, followed by storage on carbon structural defects through either chemical bonding or intercalation.