NOVELTY - The hydrogen storage tank comprises an outer chamber (2) and an internal structure (4) of a longitudinal axis (X) of the tank, and a heat exchange system within the internal structure. The internal structure comprises floors (E1, E2 up to En) extending along its planes to the longitudinal axis of the tank. Each floor comprises an inner bottom, an upper base and longitudinal partition (10) and transversal partition (12). The partitions form with the lower and upper base of compartments (8) for receiving the hydrogen storage material (6).    USE - The tank is useful for storing hydrogen by absorption in a material, where the hydrogen is useful in a fuel cell for producing electricity and in motor vehicles.    ADVANTAGE - The tank allows to store high volume density of hydrogen for a long period of time with high performance and improved environmental conditions, and avoids the accumulation of hydrogen material during storage thus preventing the damage of the tank structure.    DETAILED DESCRIPTION - The hydrogen storage tank comprises an outer chamber (2) and an internal structure (4) of a longitudinal axis (X) of the tank, and a heat exchange system within the internal structure. The internal structure comprises floors (E1, E2 up to En) extending along its planes to the longitudinal axis of the tank. Each floor comprises an inner bottom, an upper base and longitudinal partition (10) and transversal partition (12). The partitions form with the lower and upper base of compartments (8) for receiving the hydrogen storage material (6). The upper base and/or the lower base and transverse and longitudinal partitions are made of single piece and produced by folding a metal strip. The transverse partitions are fixed on the longitudinal partitions by cooperation of slots formed in the longitudinal partitions and transverse partitions. Sub-assemblies are formed by the upper base equipped with transverse and longitudinal partitions on one side and the lower base equipped with transverse and longitudinal partitions on other side. The two bases are fixed by their faces opposite to that carrying the partitions. The internal structure comprises a stack of subsets. Channels are defined between the upper and lower bases, and define the heat exchange system. The subsets are such that a longitudinal partition carried by the upper base is contained in the same plane as a longitudinal partition carried by the lower base, and in which the channels are defined along the longitudinal walls. The base of partitions is shaped to fix a groove having semicircular section. Pipes are housed in channels formed by two opposite grooves, and soldered on the channel walls. A unit is arranged to bring the hydrogen within the compartments formed by porous pipe. Notches are formed in the transverse partitions. The height of the tank is 50-110% of its length and 50-110% of its width. The hydrogen storage material is placed in the compartments. The material is placed in compartments in the form of ingot. A free volume representing 12-60% of the compartment volume is provided in each compartment. An INDEPENDENT CLAIM is included for a process for making a tank for storing hydrogen.    DESCRIPTION OF DRAWING(S) - The diagram shows a partial perspective view of hydrogen storage tank.    Outer chamber (2)    Internal structure (4)    Hydrogen storage material (6)    Compartment (8)    Longitudinal partition (10)    Transverse partition. (12)