NOVELTY - The hydrogen generator comprises: a container; a liquid reactant storage area (58) configured to contain a liquid comprising a first reactant; a reaction area (52) within the container; a solid (54) containing a second reactant within the reaction area and comprising a concentration gradient that varies along an axis of the solid; and a liquid delivery member for delivering the liquid to the solid in the reaction area to generate hydrogen. The solid comprises an acid having an acid concentration, a catalyst and a hydrophilic material.    USE - The generator is useful for generating hydrogen gas that is useful in a fuel cell system including a fuel cell battery, which is useful as power sources for portable electronic devices or an electrical appliance, where the fuel cell is proton exchange membrane fuel cells, alkaline fuel cells or solid oxide fuel cells.    ADVANTAGE - The hydrogen generator enables effective and efficient utilization of the solid reactant upon reaction with the liquid reactant, so that uniform reaction and pellet consumption in the hydrogen generator can be achieved, and the hydrogen generator is disposable or refillable.    DETAILED DESCRIPTION - The hydrogen generator comprises: a container; a liquid reactant storage area (58) configured to contain a liquid comprising a first reactant; a reaction area (52) within the container; a solid (54) containing a second reactant within the reaction area and comprising a concentration gradient that varies along an axis of the solid; and a liquid delivery member for delivering the liquid to the solid in the reaction area to generate hydrogen. The concentration gradient controls a reaction rate of the first and second reactants. The solid comprises an acid having an acid concentration, a catalyst and a hydrophilic material. The acid, the catalyst and the hydrophilic material vary along the axis of the solid to provide the concentration gradient. The solid has one of density or porosity that varies along the axis of the solid to provide the concentration gradient. The liquid delivery member comprises a liquid distribution portion having liquid outlets. The liquid distribution portion has first and second ends, and a liquid flow outlet greater at the first end than the second end, where the concentration gradient has a reactant concentration that is lowest at the first end and higher at the second end. The solid further comprises a first portion having a first reactant concentration and a second portion comprising a second reactant concentration. The first reactant concentration is different than the second reactant concentration. The first portion is closer to an inlet of the liquid delivery member and the second portion is closer to a distal outlet of the liquid delivery member. The hydrogen generator further comprises a third portion having a third reactant concentration, a fourth portion having a fourth reactant concentration, and a hydrogen outlet for outputting the generated hydrogen. The axis is along a length of the solid. The solid is a solid body comprising pellets. The first reactant includes water. The liquid reactant storage area is contained within the container. An INDEPENDENT CLAIM is included for a solid including a solid reactant.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross sectional view of a hydrogen generator.    Housing (50)    Reaction area (52)    Solid (54)    Liquid reactant storage area (58)    Effluent storage area. (74)