Fuel blends for hydrogen generators

Abstract

The present invention relates to improved aqueous fuels for hydrogen generators and a method for using them in the production of hydrogen. The present invention also relates to a system of using the subject aqueous fuels to generate hydrogen gas for use in a fuel cell or other device. The subject fuels contain a mixture of boron hydrides, at least one of which is a metal salt, including metal borohydrides, higher boranes and metal higher boron hydrides. The subject aqueous fuels contain a mixture of boron hydrides having a positive ionic charge (+IC) to boron ratio of between 0.2 and 0.4 or between 0.6 and 0.99. Preferred fuels contain a mixture of boron hydrides having an (+IC) to boron ratio between 0.2 and 0.3 or between 0.7 and 0.8. Mixtures containing a metal borohydride also contain a metal hydroxide to stability it against premature hydrolysis in the aqueous fuel media.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a blend of borohydride salts for use in the generation of hydrogen. BACKGROUND OF THE INVENTION [0002] It has been known for about fifty years that a variety of boron hydrides, hereafter borohydrides, especially their metal salts, are useful in the generation of hydrogen. It is also recognized that hydrogen generation takes place via hydrolysis generally catalyzed by acid or metals, as reported by Schlesinger, et al. in “Sodium Borohydride: Its Hydrolysis and Its Use as a Reducing Agent in the Generation of Hydrogen”, J. Am. Chem. Soc., Vol 75, pp 215-219, 1953, and G. W. Parshall in, “Hydrogen Generation by Hydrolysis or Alcoholysis of a Polyhydropolyborate-Group VIII Metal Mixture” U.S. Pat. No. 3,166,514. This early work has been improved upon by the development of systems for the controlled generation of hydrogen on an as-needed basis. U.S. Pat. No. 6,534,033 describes controlling the generation of hydrogen by contac...

AI Technical Summary

Benefits of technology

[0006] In accordance with the present invention, there are provided fuel blends for hydrogen generation comprising a mixture of boron hydrides, including at least one borohydride salt with a positive ion selected from the group consisting of alkali metal cations, alkaline earth metal cations, aluminum cation and ammonium cation such that the mixture possesses a predetermined molar ratio of solvated positive ionic charges (+IC) to boron atoms, whereby the solubility of the borate is maximized. Such fuel blends facilitate fuels with high gravimetric hydrogen storage that can be utilized for the generation of hydrogen with mitigated concern for premature solidification of the borate product in the hydrogen generation apparatus. Fuel blends equivalent to solutions containing between 30% and 38% by weight of sodium borohydride, and therefore, gravimetric hydrogen storage densities of between 6.4% and 8 wt-%, can be effectively hydrolyzed to produce hydrogen without the disadvantages of known fuels. There is also provided an improved method and system for the generation of hydrogen utilizing the fuel blends described herein.

Problems solved by technology

However, as the hydrolysis progresses and water is consumed as shown in Equation 1, the amount of water present and available to maintain the borate product in solution decreases.

As a result of the potential for the borate product to precipitate from solution, the concentrations of sodium borohydride in fuel solutions for hydrogen generation are limited to between about 15% and 20% by weight in spite of its comparatively high solubility.

This limitation results in a corresponding reduction in hydrogen storage capacity and would not be considered as optimal in those situations where volume is at a premium.

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