Self-assembled sheets of tailored CVD-synthesized single wall carbon nanotubes prepared in our laboratory and obtained from outside sources, have been used as the cathode in a three-electrode electrochemical cell. The nanotube cathodes are initially functionalized with Mg and Co nanoparticles by pulsed and continuous electrodeposition techniques, and hydrogen is then electrochemically adsorbed using dilute nitric acid and 6M KOH as electrolytes. Ex-situ and in-situ Raman scattering, and ex-situ thermogravimetry, thermopower, attenuated total internal reflection FTIR and prompt Gamma/neutron measurements, have been carried out. Hydrogen adsorption up to 4% by weight has been observed and carbon-hydrogen stretching modes are clearly seen in the infrared spectra. Details of the chemistry of the adsorption process and the role of the metals, will be discussed.