Abstract: The present invention concerns a hydrogen gas-generating apparatus (10) comprising (1) a reservoir (100) comprising an aqueous component (110), (2) a fuel compartment (200) comprising a solid metal borohydride fuel component (210), and (3) a reaction chamber (300) comprising an aerogel catalyst (310). A first fluid path introduces the aqueous component into the fuel compartment where the solid metal borohydride fuel component is dissolved into a liquid metal borohydride fuel component (210?). A second fluid path introduces the liquid metal borohydride fuel component into the reaction chamber to produce a hydrogen gas by means of a hydride-water oxidation reaction that is accelerated by the aerogel catalyst. The temperature and/or pressure of the reaction chamber are predetermined to maintain the water in the borate byproduct to be substantially in the liquid phase to minimize the precipitation of the borate byproduct.