Synthesis, Characterization, and Hydrogen-Storage Ability of Surface-Modified Multi-Wall Carbon Nanotubes

Carbon nanotubes (CNTs) have attracted increasing attention because of their unique structural, mechanical, and electronic properties. Surface chemistry modifications are also useful and critical to manipulate the adsorptive properties of CNTs and develop their hydrogen storage potential. Therefore, the synthesis or identification of multi-wall carbon nanotubes (MWCNTs) and H₂ storage capacity in MWCNTs were investigated. Experimentally, the MWCNTs were produced from the catalytic-assembly benzene-thermal routes by reduction of C₆Cl₆ with metallic K or Na in the presence of Co/Ni catalyst precursors at 503–623 K. The diameters of K-MWCNTs and Na-MWCNTs ranged from 30–100 and 20–60 nm, respectively. The H₂ storage capacity of MWCNTs improved by Pd or NaAlH₄ ranged from 2.5–3.5 wt%. Extended X-ray absorption fine structural (EXAFS) spectra showed that the Pd or PdCl₂ possess a Pd-Pd or Pd-Cl bond distance of 2.76 or 2.25 Å with a coordination number of 6 or 2, respectively. Therefore, Pd nanoparticles are well dispersed on MWCNTs, which may improve the H₂ storage capacity significantly.