Small sized ultra-pure hydrogen generator-electrolyzer

Abstract

A labor atory-scale model of a small-sized generator-electrolyzer for ultra-pure hydrogen (purity exceeding 99.999 % by volume) was designed, tested, and investigated. Pure hydrogen is produced as a byproduct simultaneously with the production of industrial-grade hydrogen during the electrolysis process. Th e use of Pd-cathodes ensured their high hydrogen saturation during electrolysis and, subsequently, when heated in a vacuum, enabled the production of a fl ow of ultra-pure hydrogen. It had been shown that the Pd-cathode with the mass of ≈ 15 g absorbs up to two normal liters of hydrogen during 2—3 hours electrolysis process at 1 atmosphere pressure and 40—60 °C temperature in the one wt. % soda solution in water. Such performance is more than twice that of previous similar electrolyzer designs, as well as the data reported in the literature for the regime governed by the molecular eff ect. Th ese cathodes can be used as hydrogen storage devices to supply high-purity hydrogen to various vacuum systems without the need for high-pressure hydrogen balloon. Th e eff ect of repeated hydrogen saturation of Pd-cathodes and multiple thermal cycles, including annealing the cathodes in a burning gas fl ame — on pure hydrogen production was investigated. Th e optimal electrode shapes and the distance between the anode and cathode were selected to ensure stable operation of the electrolyzer generator. Th e reasons of surface morphology and cathode shape changes, as the result of α  β phase transition in Pd following prolonged exposure to electrolytic hydrogen are also discussed.