Electrochemical hydrogen storage of carbon nanotubes and carbon nanofibers

The partially aligned carbon nanotubes are successfully prepared by catalytic decomposition of methane at the surface of wafer consisting of the oxidized and reduced product of LaNi5 hydrogen storage alloy with Ni powder. The CNTs are straight with a larger inner hollow core of 20–30 nm, whereas the long CNFs are curved with an inner hollow core of 6–10 nm. In addition, the long continuous metallic Ni nanowires with several microns in length are observed inside nanotubes after purification in concentrated hydrochloric acid. The purified partially aligned carbon nanotubes show a high electrochemical discharging capacity up to 267 mAh/g, corresponding to a hydrogen storage capacity of 1.0 wt%, while the maximal discharge capacity of carbon nanofiber electrode is 64 mAh/g, indicating that the partially aligned carbon nanotubes with open tips obtained provide a potential way to improve their electrochemical hydrogen storage due to the different structure.