NOVELTY - Device (12) for producing gaseous hydrogen, comprises: a reaction chamber (13) having a solution with a catalyst; and a tank chamber (14) comprising a reactant for reacting with the solution to produce gaseous hydrogen, where the tank chamber is provided with removable partition means for defining a first storage chamber for the reactant, and a second storage chamber for the reaction by-products, and the partition means is adjustable so that the volumes of the first and second storage chambers are variable in a complementary way with respect to each other.    USE - The device is useful for producing hydrogen gas, which is useful for generating electricity (all claimed).    ADVANTAGE - The device: is reliable; is self-emptying (in which the reaction-by-products are pushed in an autonomous way through the fluidic conduit by the same solution present inside the reaction chamber); utilizes single microfluidic unit, thus it is cost effective and facilitates substantial saving of inner energy expenditures; is versatile and produces electric power independently from the presence of a power distribution network; and provides a easy regulation of mobile separation wall that allows simultaneously to vary the volumes of the first storage chamber of the reactant and of the second storage chamber of the reaction-by-products.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a method (I) for producing gaseous hydrogen, comprising: storing a reactant in the tank chamber of the device and making a solution with a catalyst to react with the reactant for producing gaseous hydrogen and reaction-by-products; executing a partition of the tank chamber by using the removable partition means; and during step of making the solution with catalyst to react with the reactant, regulating the partition means so that the volumes of the first and second storage chambers are variable in complementary way with respect to each other;    (2) an apparatus, comprising a tank, and a divider moveably disposed within the tank and operable to partition the tank into a fuel chamber and a reaction-by-product chamber;    (3) a system, comprising: a first apparatus comprising the tank, the divider, and a fuel cell operable to convert a reaction-by-product from the reaction-by-product chamber into a signal; and a second apparatus operable to receive the signal; and    (4) a method (II) for producing electric power, comprising: either (a) allowing fuel to flow out from a fuel chamber so that a volume of the fuel chamber decreases, and (b) allowing a by-product of a reaction between the fuel and a reactant to flow into a reaction-by-product chamber so that a volume of the reaction-by-product chamber increases; or (c) changing a volume of a fuel chamber in a manner, and (d) changing a volume of a fuel-reaction-by-product chamber in an opposite manner.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the system.    Device (12)    Reaction chamber (13)    Tank chamber (14)    Separation wall (28)    Gas/liquid separator (31)