We report a study on hydrogen storage in Ca, Co, Fe, Ni, and Pd decorated multiwalled carbon nanotubes (MWCNTs) by using two techniques: volumetric and electrochemical. The results showed that hydrogen molecules are adsorbed on the defect sites and transported to the spaces between adjacent carbon via diffusion through both defect sites and opened tips into the layers. Hydrogen storage capacity can be improved in the decorated MWCNT by Co, Fe, Ni, and Ca metals in two approaches: (i) H 2 adsorption via Kubas interaction and (ii) dissociation of H 2 molecules on the metal particles. The results reveal that Pd are more effective catalyst for hydrogen storage process. It was found that dissociation of H 2 occurs on the Pd particle, and hydrogen atoms are entered into the spaces between adjacent carbon layers. They create loosely bonds of CH x species and PdÀCÀH x complex which can be decomposed easily at lower temperatures as compared to CÀH chemical bonds.

In this work, Pd nanoparticles were synthesized by pulsed nanosecond laser ablation in deionized water using Q-switched Nd:YAG and ArF excimer lasers, independently. The aim is to investigate the wavelength dependence of nanoparticle formation mechanisms using IR and UV laser irradiations. Pd nanoparticles fabricated by a Q-switched Nd:YAG laser show a perfect spherical morphology, whereas those due to the ArF excimer laser undergo fragmental shapes. Furthermore, the production rate of Pd nanoparticles generated at IR is noticeably greater than that at UV wavelength. Moreover, the plasma temperature induced by the Nd:YAG laser is higher than that generated by the ArF laser mainly due to the stronger inverse Bremsstrahlung process at the IR region. It was shown that the ArF laser fabricates palladium oxide structure with much higher rate with respect to the Nd:YAG laser.

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