Hydrogen storage in nanostructured carbons by spillover: bridge-building enhancement.

The hydrogen storage capacity in nanostructured carbon materials can be increased by atomic hydrogen spillover from a supported catalyst. A simple and effective technique was developed to build carbon bridges that serve to improve contact between a spillover source and a secondary receptor. In this work, a supported catalyst (Pd-C) served as the source of hydrogen atoms via dissociation and primary spillover and AX-21 or single-walled carbon nanotubes (SWNTs) were secondary spillover receptors. By carbonizing a bridge-forming precursor in the presence of the components, the hydrogen adsorption amount was increased by a factor of 2.9 for the AX-21 receptor and 1.6 for the SWNT receptor at 298 K and 100 kPa. Similar results were obtained at 10 MPa, indicating that the enhancement factor is a weak function of pressure. The AX-21 receptor with carbon bridges had the highest absolute capacity of 1.8 wt % at 298 K and 10 MPa. Reversibility was demonstrated through desorption and readsorption at 298 K. The bridge-building process appears to be receptor specific, and optimization may yield even greater enhancement. Using this technique, enhancements in storage of up to 17-fold on other carbon-based materials have been observed and will be reported elsewhere shortly.