Disclosed herein are multiple embodiments of a hydrogen generator (10) that measures, transports or stores a single dose of a viscous fuel component from first fuel chamber (12) in storage area (38) when the internal hydrogen pressure (44, 44′) of the hydrogen generator is high, and transports this single dose to a metal hydride fuel component in second fuel chamber (14) when the internal pressure is low, so that the viscous liquid and metal hydride fuel components react together to generate more hydrogen and to restart the cycle. The viscous fuel component can be water or alcohol, such as methanol, in liquid or gel form, and the metal hydride fuel component can be sodium borohydride or other metal hydride that chemically reacts with the viscous fuel to produce hydrogen. The metal hydride fuel component can be in solid or viscous form, e.g., aqueous form.