Hydrogen storage capacity of carbon nanotubes, filaments, and vapor-grown fibers

We have studied the sorption of hydrogen by nine different carbon materials at pressures up to 11 MPa (1600 psi) and temperatures from -80 to +500 degreesC. Our samples include graphite particles, activated carbon, graphitized PYROGRAF vapor-grown carbon fibers (VGCF), CO2 and air-etched PYROGRAF fibers, Showa-Denko VGCF, carbon filaments grown from a FeNiCu alloy, and nanotubes from MER Corp. and Rice University, We have measured hydrogen sorption in two pieces of equipment, one up to 3.5 MPa, and one to 11 MPa. The results so far have been remarkably similar: very little hydrogen sorption. In fact, the sorption is so small that we must pay careful attention to calibration to get reliable answers. The largest sorption observed is less than 0.1 wt.% hydrogen at room temperature and 3.5 MPa. Furthermore, our efforts to activate these materials by reduction at high temperatures and pressures were also futile. These results cast serious doubts on any claims so far for room temperature hydrogen sorption in carbon materials larger than a 1 wt.%. (C) 2001 Elsevier Science Ltd. All rights reserved.