No abstract

Substantial levels of hydrogen, up to 6.5 wt %, have been stored in carbon nanofibers (CNFs) under conditions of 12 MPa pressure and ambient temperature. The magnitude of this result cannot be interpreted in terms of physisorption on the external surface alone. Kinetic studies indicate that a slow chemisorption process is involved. The rate of uptake corresponds to that of hydrogen dissociation on graphite edge sites. Such a finding proposes a novel mechanism, offering a plausible explanation for these unusually high experimental observations. This involves the initial dissociation of hydrogen, believed to be catalyzed by carbon edge sites, which constitute the majority of the nanofiber surface, a property which is probably an important contributory factor toward their high hydrogen storage capacities.

A fuel cell operating with aqueous sodium borohydride and hydrogen peroxide streams, with one, two and four cells (electrode area 64, 128 and 256 cm 2 ) connected in a bipolar mode in a filterpress flow cell is reported. The oxidation of borohydride ion was carried out on Au/C particles supported on a carbon felt electrode while the reduction of hydrogen peroxide was carried out on carbon supported Pt on a carbon paper substrate. Comparable cell potentials and power densities to direct borohydride fuel cells reported in the literature were obtained. The challenges to further development includes: increasing the low current density and avoid decomposition of borohydride and peroxide ions. The maximum power obtained at 20• C for one, two and four cell stacks was 2.2, 3.2 and 9.6 W (34.4, 25 and 37.5 mW cm −2 , respectively) with cell voltages of 1.06, 0.81 and 3.2 V at current densities of 32, 16 and 12 mA cm −2 , respectively.

No abstract