The amount of hydrogen reversibly stored on an activated carbon electrode using electrodecomposition of 6 mol.L-1 KOH aqueous solution has been investigated. 1.5 wt % of hydrogen was released from carbon during the oxidation process, with a well-defined plateau at ca. -0.5 V vs. Hg/HgO. This is higher than the amount adsorbed under ambient gas atmosphere. This enhancement is thought to be due to the formation of nascent hydrogen during water reduction, which penetrates easily in the carbon nanostructure. Our results show that not only carbon nanotubes should be considered as hydrogen reservoir and that low cost materials such as activated carbons could be convenient in appropriate conditions.