NOVELTY - A hydrogen generator (101) comprises a fluid chamber (103) containing a fluid; a catalytic chamber (109) containing a catalyst; a reaction chamber (105) containing a hydrogen-containing material (e.g. sodium borohydride) that reacts with the fluid in the presence of the catalyst to generate hydrogen gas; and a valve (107) movable from a first position in which the flow of fluid from the fluid chamber to the catalyst chamber is enabled, to a second position in which the flow of fluid from the the fluid chamber to the catalyst chamber is disabled.    USE - As a hydrogen generator for generating hydrogen gas (claimed), useful in e.g. fuel cells and combustion engines; and can be incorporated into hand-held devices and lap-top computers.    ADVANTAGE - The hydrogen generator offers fast response time to the need for hydrogen gas, thus providing a supply of hydrogen gas on demand; and can effectively halt the production of hydrogen gas when the demand for hydrogen is reduced, so that excess hydrogen is not generated. The hydrogen generator exhibits minimum dimensions, weight and space requirements. The hydrogen generator can be placed on back of a hand-held device, or incorporated in laptop computers.    DETAILED DESCRIPTION - A hydrogen generator (101) comprises a fluid chamber (103) containing a fluid; a catalytic chamber (109) containing a catalyst; a reaction chamber (105) containing a hydrogen-containing material (e.g. sodium borohydride) that reacts with the fluid in the presence of the catalyst to generate hydrogen gas; and a valve (107) movable from a first position in which the flow of fluid from the fluid chamber to the catalyst chamber is enabled, to a second position in which the flow of fluid from the the fluid chamber to the catalyst chamber is disabled. The valve is preferably a diaphragm valve or a piezoelectric actuator. The hydrogen generator further comprises a separator (111) for separating the catalyst and a mixture of the fluid and the hydrogen-containing material, when pressure of hydrogen gas within the catalyst chamber reaches a predetermined level; and a by-product chamber (113) for holding by-products of the hydrogen-generation reaction. An INDEPENDENT CLAIM is included for a method for forming a catalytic chamber/reactor for a hydrogen generator, involving providing a core of first material, with at least one groove in a surface of the core; and covering the groove with a second material (e.g. adhesive tape), to form a passageway between the core and the second material; where the passageway includes a hydrogen generation catalyst disposed on its surface.    DESCRIPTION OF DRAWING(S) - The figure shows a perspective view of a hydrogen generator.    hydrogen generator (101)    fluid chamber (103)    reaction chamber (105)    valve (107)    catalytic chamber (109)    separator (111)    by-product chamber. (113)