Electrochemical storage of hydrogen in carbon nanotubes

The electrochemical hydrogenation property of carbon nanotubes (CNTs) was investigated. The CNTs were prepared by different methods, including chemical vapor deposition (CVD) using different catalysts (Co, Ni, etc.) or laser ablation (LA) using Co or Ni catalyst. All of the CNTs contained various amounts of residual metal catalyst. A high discharge capacity of 197 mAh/g of the CVD-Co electrode was obtained, followed by CVD-Ni (48 mAh/g) and LA (36 mAh/g) at room temperature. If the CNTs were purified by HNO3 and similar test was conducted, it was found that the discharge capacities were dramatically reduced. When the purified CNTs were deposited with a controlled amount of metal on the surface, the discharge capacity was improved significantly. It is postulated that the electrochemical hydrogen storage by carbon nanotubes might be influenced by the catalytic effect.