NOVELTY - Producing hydrogen gas using a hydrogen generator (14) comprising container and reaction area within the container, involves: moving a fluid comprising first reactant from reactant storage area to the reaction area to react the reactant in the area to produce hydrogen gas; and injecting a quantity of high pH solution having a pH value above 7.0 into reaction area to stop the reaction when hydrogen gas is not demanded. The method further involves detecting electrical power demand, where the high pH solution is injected into the area when electrical power is no longer demanded.    USE - For producing hydrogen gas (claimed) which is used as a fuel.    ADVANTAGE - When electrical power is no longer demanded and hence hydrogen gas is no longer required to be generated, the hydrogen generator injects a predetermined quantity of high pH solution into the reaction area so as stop or at least significantly curtail the reaction. This advantageously prevents excessive generation of hydrogen gas that quickly stopping the reaction and allows for components of the hydrogen generator to be manufactured with reduced pressure and leakage requirements.    DETAILED DESCRIPTION - Producing hydrogen gas using a hydrogen generator (14) comprising a container and a reaction area within the container, involves: moving a fluid comprising a first reactant from a reactant storage area to the reaction area to react the reactant in the reaction area to produce hydrogen gas; and injecting a quantity of high pH solution having a pH value above 7.0 into the reaction area to stop the reaction when hydrogen gas is not demanded. The method further involves detecting electrical power demand, where the high pH solution is injected into the reaction area when electrical power is no longer demanded. The high pH solution has a pH value of 12-14. The high pH solution is contained within a solution storage area within the container. The method further involves using a pump (22) to pump the high pH solution from the solution storage area through a fluid passage into the reaction area. INDEPENDENT CLAIMS are included for the following:    (1) a hydrogen generator comprising: a container; a reaction area within the container; a fluid comprising a reactant; and a high pH solution, where the fluid comprising the reactant moves to the reaction area to react to produce hydrogen gas, and the high pH solution is injected into the reaction area to stop the reaction when hydrogen is no longer demanded; and    (2) a fuel cell system comprising: fuel cells; hydrogen generator comprising container, first reactant, optional second reactant and reaction area; reactant storage area containing a fluid comprising the first reactant; solution storage area containing a high pH solution; and controller for controlling the injection of the fluid into the reaction area and the injection of the high pH solution, where a quantity of high pH solution is injected into the reaction area to stop the reaction.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a fuel cell system including a hydrogen generator having a high pH solution for controlling the reaction.    Fuel cell system (10)    Fuel cell stack (12)    Hydrogen generator (14)    Outlet valve (16)    Fluid outlet passage (18A)    Pump (22)    Power output (28)