Porous carbon materials, with different porosities and surface chemistry have been prepared and characterized to obtain a better understanding of the mechanism of the electrochemical storage of hydrogen. The hydrogen storage capacity depends, not only on the porosity of the material, but also on the surface chemistry, which is a critical factor. The results show that the higher the amount of surface oxygen groups, the lower is the hydrogen uptake. Measurement of the number of active carbon sites shows the important role of the unsaturated carbon atoms in the process. In situ Raman spectroscopy has been used in order to further explore the structural changes in the carbon material during the charge–discharge processes. This technique has allowed us to observe the formation of the C(sp2)AH bonds during the cathodic process and its reversibility during the oxidation step. ; MEC and FEDER for financial support (Project CTQ2006-08958/PPQ) and Ministerio de Fomento (70012/t05-fomento05 project).