A reaction hydrogen production control mechanism is provided that includes, a solid sodium borohydride mixture, a liquid fuel reactant, at least one liquid delivery medium (LDM), a movable boundary interface (MBI) and a reaction zone, where the MBI is disposed to provide a constant contact between a reacting surface of the solid fuel mixture and the primary LDM to form the reaction zone. A reaction in the reaction zone includes a hydrolysis reaction. The MBI moves according to a spring, gas pressure, or an elastic membrane. Product paths are disposed to transfer reactants from the system. The product paths can include a channel on a surface of the solid fuel mixture, a channel disposed through the solid fuel mixture, a channel disposed about the solid fuel mixture, a contained region disposed about the solid fuel mixture, or a conduit abutting the solid fuel mixture.