The apparatus includes a liquid permeable pouch that defines a cavity for maintaining an anhydrous hydride reactant, wherein the cavity comprises a cross-section such that a point within the cross-section is separated from a perimeter of the liquid permeable pouch by no more than double the permeation distance, and a cartridge configured to receive the liquid permeable pouch and a liquid reactant such that at least a portion of the liquid permeable pouch is submerged in the liquid reactant. The system includes a plurality of pouches formed from two rectangular sheets of liquid permeable material, and each pouch has a width selected such that each point within a cross-section is separated from the sheets by no more than double the permeation distance. The method includes joining the sheets, forming one or more seals to define a cavity, disposing anhydrous hydride within the cavity, and sealing the opening.