US20050132640A1

US20050132640A1 - Fuel blends for hydrogen generators

Info

Publication number: US20050132640A1
Application number: US10/741,199
Authority: US
Inventors: Michael Kelly; Ying Wu; Jason Brady; M. Hawthorne
Original assignee: Millennium Cell Inc
Current assignee: Millennium Cell Inc
Priority date: 2003-12-19
Filing date: 2003-12-19
Publication date: 2005-06-23
Also published as: WO2005065119A2; CA2550473A1; EP1713890A2; JP2007520410A; WO2005065119A3; CN1918268A; KR20070009981A

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

The present invention relates to a blend of borohydride salts for use in the generation of hydrogen.

BACKGROUND OF THE INVENTION

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 contact of an aqueous solution of borohydride by pumping the solution through a chamber containing a metal catalyst thereby converting the borohydride to hydrogen gas and borate salts in near quantitative yield according to Equation 1:
MBH₄+2H₂O→4H₂+MBO₂ (1)
There are a number of factors governing the selection of particular borohydride salts for use in the process illustrated in Equation 1. Primary among these is solubility in water. Borohydrides generally possess a solubility in water of from about 7% to about 35% by weight at 25° C. Lithium borohydride has a solubility of 7%, potassium borohydride is about 19%, and sodium borohydride is soluble at about 35%. For this reason, as well as some others, notably including safety and convenience, sodium borohydride is the salt of choice for fuel solutions for a hydrogen generator. Sodium borohydride, which possesses a high gravimetric hydrogen storage density of about 7.4 wt. percent in a saturated solution at ambient temperature, is preferred in the practice of the present invention as well.
In a concentrated solution of sodium borohydride, such as described above, there is initially sufficient water for the complete hydrolysis of the sodium borohydride as well as for maintaining the borate product in solution. 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. In the event the amount of water in the system declines to the point where the borate salt precipitates out of solution in the catalyst reactor, or in any of the plumbing connecting the storage tanks to the reactor, the hydrogen generator could become progressively blocked to the point where it would have to be stopped, disassembled and cleaned.
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. Such solutions represent about 4.25 Wt.-% hydrogen generated. This is recognized as being the practical limit for hydrogen generation, see for example, Von Dohren, “Raney Catalyst for Generating Hydrogen by Decomposition of Boranes”, U.S. Pat. No. 3,615,215. 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. Typically, such is the situation, and it is especially desirable to have a hydrogen-dense fuel to maximize the amount of hydrogen stored per unit volume of fuel. Such fuels are provided in accordance with the present invention.

SUMMARY OF THE INVENTION

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.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to aqueous fuels for hydrogen generation containing certain mixtures of boron hydrides. Boron hydrides in this context refer to boranes, including polyhedral boranes, and anions of borohydrides or polyhedral boranes. More particularly, the present invention relates to aqueous fuels containing blends of boron hydrides having a predetermined molar ratio of solvated positive ionic charges (⁺ICs) to boron atoms. It has been found that this ratio results in a solubility maximizing, not of the components of the fuel, but of the borate product of the hydrolysis reaction that results in the generation of hydrogen. By solubility maximizing in this context is meant achieving optimum solubility of the borate product in relation to the concentration of the borohydrides in the fuel, thereby minimizing the incidence of precipitation of borate product during the generation of hydrogen as a result of the consumption of water in the hydrolysis of boron hydrides, for example, as shown for the borohydrides in Equation (1).
The ratio of positive ionic charges (+IC) to boron is determined in accordance with the present invention in the following manner, using alkali metal salts as an example. Alkali metal borate salts are typically written in the format j M₂O.k B₂O₃.X H₂O, wherein M is chosen from lithium, sodium and potassium. The values for j, k and X will vary for different borates. For example, the mineral Borax has j=1, k=2, and X=10 and, therefore, can be written Na₂O.2B₂O₃.10H₂O or Na₂B₄O₇.10H₂O. Those of ordinary skill in the art recognize that nearly any ratio of j to k will form a solid crystal borate salt, but the solubility of such crystals in water will vary. There are two temperature dependent solubility maxima occurring at j to k ratios between 0.2 and 0.4 and again at ratios between 0.6 and 0.99.
The solubility of borates as a function of the value of the j to k ratios discussed above have been known for many years. See for example, Nies and Holbert, Journal of Chemical and Engineering Data, Vol. 12, No. 3, pp 303-313, 1967, Adams, “Boron, Metallo-Boron Compounds and Boranes” John Wiley & Sons, page 81, 1964, and Garret, “Borates, Handbook of Deposits, Processing, Properties and Use”, Academic Press, 1998, page 454. Salts in the formula given above wherein M is potassium or lithium have similar solubility maxima, Adams ibid, pp 81 and 83, Reburn and Gale, Journal of Physical Chemistry, Vol. 59, No. 19, 1955. While such values, along with countless others, have been available in the open literature for many years, their value in the determination of fuel blends for hydrogen generators has heretofore been unrecognized.
In accordance with the present invention, fuel blends for hydrogen generators are chosen to comprise a mixture of boron hydrides such that the value of the molar ratio of positive ionic charges (⁺ICs) to boron atoms is between 0.2 to 0.4, preferably between 0.2 and 0.3, or between 0.6 and 0.99, preferably between 0.7 and 0.8. The fuel mixtures in accordance with the present invention are comprised of a boron hydride salt wherein the positive ion (M) is selected from those of an alkali metal such as sodium, lithium, potassium, an alkaline earth metal, aluminum or ammonium in combination with at least one other boron hydride such that the desired ratios are achieved. Suitable boron hydrides include, without intended limitation, the group of borohydride salts (MBH₄), triborohydride salts (MB₃H₈), decahydrodecaborate salts (M₂B₁₀H₁₀), tridecahydrodecaborate salts (MB₁₀H₁₃), dodecahydrododecaborate salts (M₂B₁₂H₁₂), and octadecahydroicosaborate salts (M₂B₂₀H₁₈) and related neutral borane compounds that are compatible with the boron hydride salts, such as decaborane(14) (B₁₀H₁₄), where M is an alkali metal, alkaline earth metal, or aluminum cation.
It is within the scope of the present invention to utilize mixtures of such higher boron hydrides such that the desired molar ratio of positive ionic charges (⁺ICs) to boron atoms is achieved. Although such mixtures may contain boranes, such as those given above, it is necessary to also have at least one boron hydride salt so that the desired (⁺ICs) to boron ratio is achieved. Preferred mixtures of positive ion boron hydrides in accordance with the present invention include, without intended limitation: a metal borohydride, preferably sodium borohydride, and decaborane(14); a metal triborohydride and a metal dodecahydrododecaborate; a metal borohydride and a metal triborohydride; and a metal borohydride and a metal dodecahydrododecaborate. It is not critical whether the mixtures of boron hydrides in the subject fuels have an ⁺IC/B ratio falling between 0.2 to 0.4 or between 0.6 and 0.99 as both are advantageous. The selection of component boron hydrides and the resultant ⁺IC/B ratio may be determined by economic considerations, e.g., the relative availability and cost of the individual boron hydride compounds, as well as consideration of the chemical reactivity and human health effects of the individual boron hydride compounds. Whether a particular mixture is within one or the other may be determined by other considerations, such as relative solubility of various boron hydrides, desired operating temperature range of the mixture and the like, and is considered to be within the purview of one of ordinary skill in the art.
The positive ion component of the higher borohydrides described above may be, in addition to the alkali metal cations as described in reference to the borohydrides, alkaline earth metal cations, or aluminum cation. Preferably, the positive ion is selected from sodium, lithium, potassium, beryllium, magnesium, calcium, or aluminum. It is not a requirement that where the subject fuel mixtures contain more than one borohydride salt, the positive ion components thereof be the same. As stated above, the positive ion component for the metal borohydrides of the subject fuel blends is preferably sodium. Those of ordinary skill in the art recognize that, wherein a borohydride salt is present in aqueous fuel mixtures for hydrogen generators, it will readily hydrolyze unless it is stabilized against hydrolysis by the presence of a strong base. Suitable bases for this purpose are the hydroxides of the respective metals given above that are strong bases, e.g. sodium hydroxide when the component is sodium borohydride. In preferred fuel mixtures in accordance with the present invention that contain a borohydride salt, the positive cation component of the stabilizer must enter into the equation when the mole ratio of positive ionic charge (⁺IC) to boron is calculated as will be discussed below. Likewise, in order to prepare stable aqueous solutions of decaborane(14), an alkaline stabilizer must be present; the metal cation component of the stablizer contributes positive ionic charge (⁺IC) to the fuel blend. Many of the boron-rich hydrides (such as the M₂B₁₂H₁₂, M₂B₁₀H₁₀, and M₂B₂₀H₁₈) are stable in neutral aqueous solution.
In accordance with the present invention, the calculation of the mole ratio of positive ionic charge (⁺IC) to boron is developed in the following manner. As an illustration, an aqueous fuel solution containing 35% by weight sodium borohydride as the only positive ion boron hydride with 3% by weight sodium hydroxide added for stability has a j to k ratio of 1.08 determined as follows using 100 grams of fuel solution as an example. In the example, all boron comes from the sodium borohydride, therefore the number of moles of boron is calculated directly from the borohydride concentration in the fuel solution as shown below. $20 g {NaBH}_{4} (\frac{1 mol {NaBH}_{4}}{37.83 g {NaBH}_{4}}) (\frac{1 mol B}{1 mol {NaBH}_{4}}) = 0.529 mol B$
Utilizing the same calculation, it is known that sodium borohydride provides 0.925 moles of Na as well since sodium and boron exist in a 1:1 molar ratio therein. However, there is additional sodium (⁺IC) provided by the sodium hydroxide stabilizer, which can be determined in a manner similar to the determination of the boron contribution as shown below. $3 g NaOH (\frac{1 mol NaOH}{40.00 g NaOH}) (\frac{1 mol Na}{1 mol NaOH}) = 0.075 mol Na$
Once the moles of sodium, equivalent to the positive ionic charge (⁺IC) is known, the ratio can be calculated by dividing the total moles of sodium by the total number of moles of boron as illustrated below: $(\frac{0.529 mol Na + 0.075 mol Na}{0.529 mol B}) = 1.14 Na : B$
Therefore, a solution containing 35% by weight sodium borohydride and 3% by weight sodium hydroxide would have a (⁺IC) to boron ratio of 1.08 which is outside of the maximum solubility range ratios as stated above. This would effectively limit the use of such concentrated fuel solutions in a hydrogen generator without the input of additional water as the reaction continues to ensure that the borate product would remain in solution and not precipitate causing clogging of the apparatus.
The presence of higher boron hydrides in the fuel solution as described above would adjust the j to k ratio downward to the preferred ratios of this invention because the higher boron hydrides are rich in boron in relation to the metal component of the fuel mixture. As the solubility of the product borates from such fuels is markedly higher than with a conventional aqueous sodium borohydride solution, greater amounts of borohydride and, hence, greater amounts of hydrogen are contained in the fuel solution due to the reduced risk of solidification of the borate product. A further advantage of the fuel mixtures of the present invention is that many of the boron-rich higher boron hydrides are stable in aqueous solution and do not require the addition of basic stabilizers as is the case with metal borohydrides, such as sodium borohydride. An additional advantage of the subject blended fuel solutions is that some higher boron hydrides hydrolyze in aqueous solution to yield some acidic products which, in turn, could act to partially neutralize any metal hydroxide stabilizer present and produce a less basic discharge stream than the metal metaborate/metal hydroxide mixture that results from using a fuel containing only metal borohydride and metal hydroxide.
An additional advantage to the novel aqueous fuel blends of the present invention is the fact that, even if some solidification were to take place in the hydrolysis reactor as cooling takes place, the products are readily water soluble. In contrast, the borate mixtures that are formed when the fuel contains only metal borohydride and hydroxide, e.g. sodium borohydride and hydroxide, are slow to dissolve and can form a crust in the catalyst chamber that is difficult to remove. The borate mixtures formed with use of the fuel mixtures of the present invention can be readily removed by the simple expedient of flushing the chamber and related apparatus with water, thereby prolonging catalyst life and reducing normal maintenance downtime for hydrogen generation systems. The ease of cleaning as well as the increase in the interval between required cleaning and maintenance operations of hydrogen generation systems are a distinct economic advantage of the fuel mixtures of the present invention.
The explanation for the solubility difference between the products formed from the fuel mixtures of the present invention in comparison to fuel mixtures containing only a metal borohydride, such as sodium borohydride, is the negative heat of solvation typically associated with borates. Sodium metaborate, for example, exhibits substantial cooling of the solvent when going into solution, thereby slowing the dissolution reaction. In contrast, sodium borate salts having molar ratios of positive ionic charge (⁺IC) to boron within the maximum solubility ranges in accordance with the present invention can have positive heats of solvation and, therefore, actually facilitate the dissolution reaction and, thereby, the production of hydrogen, see O'Brien et al, “Amorphous Sodium Borate Composition” U.S. Pat. No. 2,998,310.
The term “aqueous fuel”, as utilized herein, includes an aqueous liquid in which all the components are dissolved and/or a slurry in which some of the components are dissolved and some of the components are undissolved solids. Hydroalcoholic mixtures are also advantageous for preparing the aqueous fuels of the present invention in that they lower the freezing point of the fuel, thereby expanding the operating temperature range thereof. In general, the higher boron hydrides tend to be both soluble and stable in hydroalcoholic solutions, especially when a stabilizer is present to raise the pH. The alcohols utilized to prepare hydroalcoholic solutions are lower alkanols, particularly methanol and ethanol. It is contemplated herein that aqueous fuels prepared in the form of slurries for economy of handling and storage will be combined with sufficient water at time of use to form solutions of the components confirming to the ratios of maximum solubility stated herein.
In accordance with the present invention, there are provided an improved method and system for generating hydrogen. The method comprises contacting the subject improved aqueous fuel blend of boron hydrides having specific positive ionic charge (⁺IC) to moles of boron ratios with a catalyst for promoting the hydrolysis of the boron hydrides to produce hydrogen. The system provided in accordance with the present invention includes means for contacting the aqueous fuel blends of boron hydrides with the catalyst. Such means include means to physically separate the catalyst from the fuel when there is no demand for hydrogen gas. When there is a demand for hydrogen, the aqueous fuel solution can be brought into contact with the catalyst so that the hydrolysis reaction occurs and hydrogen is produced. The separation of catalyst can be achieved by using any mechanical, chemical, electrical and/or magnetic method that can readily appreciated by a person skilled in the art. In one embodiment, different chambers are used to separate the catalyst from the aqueous fuel solution. The aqueous fuel can be stored in a fuel reservoir, from which it is pumped into the catalyst chamber to contact the catalyst thereby generating hydrogen through the hydrolysis reaction illustrated in Equation (1) for metal borohydrides. In an alternative embodiment, the catalyst can be inserted into and removed from a tank containing the subject hydride solution.
In a further embodiment, the catalyst for the hydrolysis is an acid and both the fuel and the catalyst are in liquid form which can be pumped into the reaction chamber to generate hydrogen. In this embodiment, the fuel and the catalyst solution must be stored in separate containers and individually pumped into the reactor to initiate and maintain the hydrolysis reaction. Preferred acid catalysts are strong inorganic acids, particularly hydrochloric acid sulfuric acid and phosphoric acid.
The improved fuel solutions of the present invention may be pumped into the system either batchwise or continuously. Further, the catalyst chamber may comprise at least one conduit, through which fuel solution can be directed to flow into and out of the chamber at different stages of the catalysis reaction. The conduit may also function as output channel for discharging hydrogen gas generated by the hydrolysis reaction.
It is important to note that a separate chamber may not be necessary when insoluble metals or metals bound to, entrapped within, and/or coated onto a substrate are used as the catalyst in reaction illustrated in Equation (1). Suitable substrates for metal catalysts include, without intended limitation, plastics, polymers, textiles, metals, metal oxides, ceramics, or carbonaceous materials. In a preferred embodiment, the system of the present invention includes a containment system wherein the catalyst is entrapped by physical or chemical means onto and/or within a porous or nonporous substrate, including metallic meshes and fibers as shown in U.S. Pat. No. 6,534,033, which is incorporated by reference herein. In any of these embodiments, the hydrogen generation system may comprise only one chamber, wherein the separation of the catalyst from the aqueous fuels can be achieved by removing the insoluble or supported catalyst from the solution thereby interrupting contact between the catalyst and the boron hydrides therein. Consequently, when hydrogen production is desired, the catalyst can simply be reinserted into the aqueous fuel to catalyze reaction (1) as described above.
Since the improved aqueous fuels of the present invention are stable in the absence of a catalyst, the generation of hydrogen in accordance with reaction (1) can be closely controlled by regulating the contact of boron hydrides therein with catalyst. The control can be achieved by regulating the flow of aqueous fuel to the catalyst, or by withdrawing the catalyst from the fuel solution, depending on the actual setup of the hydrogen generating system and the configuration thereof. In a system that uses a supported or deposited catalyst, hydrogen production can be controlled by contacting with or separating the bound catalyst from the boron hydride fuel solution. For example, the catalyst metal can be attached to a piston or the like, which can move in and out of the fuel solution in response to hydrogen demand. Alternatively, the supported catalyst can be contained in a separate chamber and the flow of the fuel solution into the chamber is controlled by valves and a suitable regulator means. For a homogeneous catalyst, e.g. an acid solution, the control of hydrogen generation is achieved by regulating the flow of either the boron hydride fuel solution, or the catalyst solution, or both. Preferably, a mixing chamber is used wherein the two solutions are injected or pumped into the chamber so that they are mixed and the hydrolysis reaction will occur.
In another embodiment, the acidic salts of polyhedral boron hydrides, such as hydronium salts, wherein the positive ion is H⁺, and ammonium salts, wherein the positive ion is NH₄ ⁺, can be used as a combination fuel component and accelerant for the generation of hydrogen. Suitable accelerant components include H₂B₁₂H₁₂, H₂B₁₀H₁₀, (NH₄)₂B₁₂H₁₂, and (NH₄)₂B₁₀H₁₀. In such a system, no additional catalyst system is required, though one may be incorporated as needed to optimize hydrogen generation rate. In this embodiment, an acidic polyhedral boron hydride salt (accelerant) is stored separately from a fuel mixture comprising one or more boron hydrides, and the species combined as needed to produce hydrogen. It is preferable that at least one of the accelerant or fuel mixture be an aqueous solutions to facilitate mixing. However, either or both components (the fuel blend and the accelerant) may be stored as a dry powder to eliminate the need for a stabilizer. In such a case, a separate supply of water is required for hydrogen generation, and the dry and liquid components are added in defined proportions to a mixing chamber by using any method known to those skilled in the art. The boron hydride species, concentrations and mixing rates are chosen in accordance with the present invention as described above such that the resultant borate salts have the appropriate ⁺IC/B ratio falling between 0.2 to 0.4 or between 0.6 to 0.99. For the purpose of this calculation only, the hydronium salts are treated as neutral boron hydrides, e.g. H₂B₁₂H₁₂is treated as B₁₂H₁₄in order to determine the boron contribution. When hydrogen generation is desired, the accelerant is metered into a reactor to mix with the boron hydride fuel mixture and with any necessary water. The acidic polyhedral boron hydride salt thus acts as an accelerant to promote the hydrogen generation reaction, hydrolyzes to produce hydrogen, and, contributes boron atoms, and in the case of the ammonium salts, positive charge, to the fuel blend.
It has been found that the hydrogen gas formed in the hydrolysis reaction is co-eluted with the liquid borate product. Consequently, in a preferred embodiment, a gas-liquid separator is used to separate hydrogen gas from the effluent solution. Additionally, in order to accommodate immediate demand for hydrogen gas, it is preferred to incorporate a small buffer tank into the present system. In such an embodiment, the small buffer tank always contains a supply of hydrogen gas for instantaneous demand for hydrogen. Once hydrogen is withdrawn from the buffer tank, the resulted pressure drop can trigger the system to produce more hydrogen gas so that a constant level of hydrogen gas is maintained therein.
The hydrogen gas generated by the current system can be directed to a fuel cell or a hydrogen-consuming device for direct use. In the alternative, the hydrogen gas can be stored in a gas reservoir or buffer tank as described above for future use.
The fuel blends prepared in accordance with the present invention are governed by two considerations. The first of these is the mole ratio of positive ionic charge (⁺IC) to atomic boron as discussed herein. The second is the relative solubilities of the individual salts utilized to form the mixture. It will be appreciated that one of ordinary skill in the art, given the parameters of the maximum ratios discussed herein and with the relative solubilities of individual salts, which information is readily available, would be able to prepare a fuel solution that would possess a maximum ratio and all components would be soluble in the aqueous vehicle. Such calculations are illustrated by the following examples which are for purposes of illustration and are not intended to be limiting on the scope of the present invention.

EXAMPLE 1

Generic Procedure for Hydrogen Generation from Fuel Blends
A generic description of a hydrogen generation test is described, using sodium borohydride, decaborane, sodium hydroxide and water in the fuel blend as a sample system. Fuel blends are made in open air. The water and stabilizing sodium hydroxide are initially mixed, decaborane is added thereto, followed by the proper amount of sodium borohydride to deliver the desired ratio.
To catalytically discharge the fuel blend, a Parr reactor resting on a hot plate is employed. The reactor incorporates two thermocouples that operated continuously during the run, one measuring the temperature of the fuel solution, and the other measuring the temperature of the head-space near the top of the reactor. The second thermocouple controls a cooling loop circulating through the reactor that is activated when the second thermocouple records a threshold temperature of 95° C. As a practical matter, however, even with the hot plate the reaction temperature rarely exceeds 90° C. A pressure sensor continually measures internal pressure. The reactor is first charged with six pieces of ruthenium coated nickel catalyst, each piece weighing between 0.095 and 0.105 g. Approximately 10 grams of fuel blend (the weight was known precisely for each run) is injected through an inlet port, and the port sealed. The hot plate is then turned on. When the pressure has ceased to increase at an appreciable rate, the hot plate is turned off and the reactor allowed to cool to room temperature. When the average gas temperature at the top of the reactor matches the average temperature of the reaction solution, the data acquisition is halted, and the final pressure measured. The final pressure and temperature along with the reactor volume can be used to calculate the molar yield of hydrogen gas. The molar yield is then compared to the expected yield from the amount and concentration of fuel to determine a percent yield.
Thermal decomposition is accomplished in the same fashion as a catalytic discharge, but the Parr reactor was not charged with catalyst and only heat from the hot plate is responsible for hydrolysis of the blend.

EXAMPLE 2

7.0 wt-% Hydrogen, ⁺IC/B Ratio=0.8
The following were mixed according to the procedure of Example 1 to yield 100 g of a fuel blend capable of delivering 7.0 weight-% H₂, with a sodium to boron ratio of 0.8: sodium borohydride 27.16 g; sodium hydroxide 3 g; decaborane(14) 3.34 g and water 66.5 g. Each mole of sodium borohydride yields four moles of hydrogen according to the equation (1) above
NaBH₄+2H₂O→NaBO₂+4H₂ (1)
And each mole of decaborane(14) yields twenty-two moles of hydrogen according to equation (2)
B₁₀H₁₄+15H₂O→5B₂O₃+22H₂ (2)
The hydrogen storage capacity of this blend is determined by calculating the total number of moles of H₂produced and divided by the initial weight of the blend. $27.16 g {NaBH}_{4} (\frac{1 mol {NaBH}_{4}}{37.83 g {NaBH}_{4}}) (\frac{4 mol H_{2}}{1 mol {NaBH}_{4}}) (\frac{2.0158 g H_{2}}{1 mol H_{2}}) = 5.79 g H_{2} from {NaBH}_{4}$ $3.34 g B_{10} H_{14} (\frac{1 mol B_{10} H_{14}}{122.21 g B_{10} H_{14}}) (\frac{22 mol H_{2}}{1 mol B_{10} H_{14}}) (\frac{2.0158 g H_{2}}{1 mol H_{2}}) = 1.21 g H_{2} from B_{10} H_{14}$
The total hydrogen yield is 5.79+1.21=7 grams, or 7% by weight.
The ⁺IC:B ratio is calculated as follows: $27.16 g {NaBH}_{4} (\frac{1 mol {NaBH}_{4}}{37.83 g {NaBH}_{4}}) (\frac{1 mol B}{1 mol {NaBH}_{4}}) = 0.718 mol B from {NaBH}_{4}$ $3.34 g B_{10} H_{14} (\frac{1 mol B_{10} H_{14}}{122.21 g B_{10} H_{14}}) (\frac{10 mol B}{1 mol B_{10} H_{14}}) = 0.273 mol B from B_{10} H_{14}$ $27.16 g {NaBH}_{4} (\frac{1 mol {NaBH}_{4}}{37.83 g {NaBH}_{4}}) (\frac{1 mol {Na}^{+}}{1 mol {NaBH}_{4}}) (\frac{1 mol^{+} IC}{1 mol {Na}^{+}}) = 0.718 mol^{+} IC from {NaBH}_{4}$ $3.00 g NaOH (\frac{1 mol NaOH}{40.00 g NaOH}) (\frac{1 mol {Na}^{+}}{1 mol NaOH}) (\frac{1 mol^{+} IC}{1 mol {Na}^{+}}) = 0.075 mol^{+} IC from NaOH  (\frac{0.718 + 0.075 mol^{+} IC}{0.718 + 0.273 mol B}) = 0.800^{+} IC : B$
Therefore this blend has a Na:B mole ratio of 0.8.

EXAMPLE 3

6.8 wt-% Hydrogen, ⁺IC/B Ratio=0.25
The following were mixed according to the procedure of Example 1 to yield 100 g of a fuel blend capable of delivering 6.8 weight-% H₂, with a sodium to boron ratio of 0.25: sodium triborohydride 13.74 g; sodium dodecahydrododecaborate 13.74 g and water 76.09 g. Each mole of sodium dodecahydrododecaborate yields twenty-five moles of hydrogen according to equation (3)
Na₂B₁₂H₁₂+19H₂O→2NaBO₂+5B₂O₃+25H₂ (3)
And each mole of sodium triborohydride yields nine moles of hydrogen according to equation (4)
NaB₃H₈+5H₂O→NaBO₂+B₂O₃+9H₂ (4)
The hydrogen storage capacity of this blend is determined by calculating the total number of moles of H₂produced and divided by the initial weight of the blend. $\begin{matrix} 10.17 g {Na}_{2} B_{12} H_{12} (\frac{1 mol {Na}_{2} B_{12} H_{12}}{187.79 g {Na}_{2} B_{12} H_{12}}) (\frac{25 mol H_{2}}{1 mol {Na}_{2} B_{12} H_{12}}) \\ (\frac{2.0158 g H_{2}}{1 mol H_{2}}) = 2.87 g H_{2} from {Na}_{2} B_{12} H_{12} \\ 13.74 g {NaB}_{3} H_{8} (\frac{1 mol {NaB}_{3} H_{8}}{63.48 g {NaB}_{3} H_{8}}) (\frac{9 mol H_{2}}{1 mol {NaB}_{3} H_{8}}) \\ (\frac{2.0158 g H_{2}}{1 mol H_{2}}) = 3.93 g H_{2} from {NaB}_{3} H_{8} \end{matrix}$
The total hydrogen yield is 2.87+3.93=6.8 grams, or 6.8% by weight. The ⁺IC:B ratio can also be calculated as follows: $10.17 g {Na}_{2} B_{12} H_{12} (\frac{1 mol {Na}_{2} B_{12} H_{12}}{187.79 g {Na}_{2} B_{12} H_{12}}) (\frac{12 mol B}{1 mol {Na}_{2} B_{12} H_{12}}) = 0.650 mol B from {Na}_{2} B_{12} H_{12}$ $13.74 g {(Na B)}_{3} H_{8} (\frac{1 mol {NaB}_{3} H_{8}}{63.48 g {NaB}_{3} H_{8}}) (\frac{3 mol B}{1 mol {NaB}_{3} H_{8}}) = 0.649 mol B from {(Na B)}_{3} H_{8}$ $10.17 g {Na}_{2} B_{12} H_{12} (\frac{1 mol {Na}_{2} B_{12} H_{12}}{187.79 g {Na}_{2} B_{12} H_{12}}) (\frac{2 mol {Na}^{+}}{1 mol {Na}_{2} B_{12} H_{12}}) (\frac{1 {mol}^{+} IC}{1 mol {Na}^{+}}) = 0.108 mol^{+} IC from {Na}_{2} B_{12} H_{12}$ $13.74 g {(Na B)}_{3} H_{8} (\frac{1 mol {NaB}_{3} H_{8}}{63.48 g {NaB}_{3} H_{8}}) (\frac{1 mol {Na}^{+}}{1 mol {NaB}_{3} H_{8}}) (\frac{1 {mol}^{+} IC}{1 mol {Na}^{+}}) = 0.216 mol^{+} IC from {NaB}_{3} H_{8} (\frac{0.108 + 0.216 mol^{+} IC}{0.650 + 0.649 mol B}) = 0.25^{+} IC : B$
Therefore this blend has a Na:B mole ratio of 0.25.

EXAMPLE 4

5 wt-% Hydrogen, ⁺IC/B Ratio=0.25
The following were mixed according to the procedure of Example 1 to yield 100 g of a fuel blend capable of delivering 5.0 weight-% H₂, having a metal cation to boron ratio of 0.25: potassium triborohydride 12.95 g; magnesium dodecahydrododecaborate 6.76 g and water 80.03 g.
Each mole of magnesium dodecahydrododecaborate yields twenty-five moles of hydrogen according to equation (5)
MgB₁₂H₁₂+19H₂O→Mg(BO₂)₂+5 B₂O₃+25H₂ (5)
Each mole of potassium triborohydride yields nine moles of hydrogen in accordance with equation (6)
KB₃H₈+5H₂O→KBO₂+B₂O₃+9H₂ (6)
The hydrogen storage capacity of this blend is determined by calculating the total number of moles of H₂produced and divided by the initial weight of the blend. $6.76 g {MgB}_{12} H_{12} (\frac{1 mol {MgB}_{12} H_{12}}{166.12 g {MgB}_{12} H_{12}}) (\frac{25 mol H_{2}}{1 mol {MgB}_{12} H_{12}}) (\frac{2.0158 g H_{2}}{1 mol H_{2}}) = 2.05 g H_{2} from {MgB}_{12} H_{12}$ $12.95 g {KB}_{3} H_{8} (\frac{1 mol {KB}_{3} H_{8}}{79.59 g {KB}_{3} H_{8}}) (\frac{9 mol H_{2}}{1 mol {KB}_{3} H_{8}}) (\frac{2.0158 g H_{2}}{1 mol H_{2}}) = 2.95 g H_{2} from {KB}_{3} H_{8}$
The total hydrogen yield is 2.05+2.95=5.0 grams, or 5% by weight. The ⁺IC:B ratio can also be calculated as follows: $6.76 g {MgB}_{12} H_{12} (\frac{1 mol {MgB}_{12} H_{12}}{166.12 g {MgB}_{12} H_{12}}) (\frac{12 mol B}{1 mol {MgB}_{12} H_{12}}) = 0.488 mol B from {MgB}_{12} H_{12}$ $12.95 g {KB}_{3} H_{8} (\frac{1 mol {KB}_{3} H_{8}}{79.59 g {KB}_{3} H_{8}}) (\frac{3 mol H_{2}}{1 mol {KB}_{3} H_{8}}) = 0.488 mol B from {KB}_{3} H_{8}$ $6.76 g {MgB}_{12} H_{12} (\frac{1 mol {MgB}_{12} H_{12}}{166.12 g {MgB}_{12} H_{12}}) (\frac{1 mol {Mg}^{2^{+}}}{1 mol {MgB}_{12} H_{12}}) (\frac{2 mol^{+} IC}{1 mol {Mg}^{2^{+}}}) = 0.081 mol^{+} IC from {MgB}_{12} H_{12}$ $12.95 g {KB}_{3} H_{8} (\frac{1 mol {KB}_{3} H_{8}}{79.59 g {KB}_{3} H_{8}}) (\frac{1 mol K^{+}}{1 mol {KB}_{3} H_{8}}) (\frac{1 mol^{+} IC}{1 mol K^{+}}) = 0.163 mol^{+} IC from {KB}_{3} H_{8} (\frac{0.081 + 0.163 mol^{+} IC}{0.488 + 0.488 mol B}) = 0.25^{+} IC : B$
Therefore this blend has a ⁺IC:B mole ratio of 0.25.

Examples 5-8

By similar calculations, the following fuel blends were prepared according to the procedure of Example 1:



	Fuel Blend
Example #	Composition	⁺IC	B	⁺IC/B	H wt %

5	3.92 g NaBH₄	0.124	0.156	0.79	5.3%
	0.78 g NaOH
	0.63 g B₁₀H₁₄
	14.69 H₂O
6	6.13 g NaBH₄	0.182	0.227	0.8	6.4%
	0.8 g NaOH
	0.8 g B₁₀H₁₄
	17.33 H₂O
7	7.26 g NaBH₄	0.214	0.263	0.81	7.5%
	0.78 g NaOH
	0.87 g B₁₀H₁₄
	16.54 H₂O
8	3.22 g NaBH₄	0.095	0.118	0.81	8.1%
	0.47 g NaOH
	0.40 g B₁₀H₁₄
	6.18 H₂O

EXAMPLE 9

5.6 wt-% Hydrogen, ⁺IC/B Ratio=0.7
To demonstrate the use of a boron hydride as an accelerant, sodium borohydride (20 mg), diammonium decahydrodecaborate (5 mg) and water (75 mg) were mixed together, accompanied by immediate and vigorous hydrogen evolution. This mixture is equivalent to a fuel blend with an +IC to boron ratio of 0.7 and capable of delivering 5.6 wt-% hydrogen. Each mole of sodium borohydride yields four moles of hydrogen according to the equation (1)
NaBH₄+2H₂O→NaBO₂+4H₂ (1)
And each mole of diammonium decahydrodecaborate yields twenty-one moles of hydrogen according to equation (7)
(NH₄)₂B₁₀H₁₀+16H₂O→2(NH₄)₂BO₂+4B₂O₃+21H₂ (7)
The hydrogen storage capacity of this blend is determined by calculating the total number of moles of H₂produced and divided by the initial weight of the blend. $20 mg {NaBH}_{4} (\frac{1 mmol {NaBH}_{4}}{37.83 mg {NaBH}_{4}}) (\frac{4 mmol H_{2}}{1 mmol {NaBH}_{4}}) (\frac{2.0158 mg H_{2}}{1 mmol H_{2}}) = 4.26 mg H_{2} from {NaBH}_{4}$ $5 mg {({NH}_{4})}_{2} B_{10} H_{10} (\frac{1 mmol {({NH}_{4})}_{2} B_{10} H_{10}}{154.26 mg {({NH}_{4})}_{2} B_{10} H_{10}}) (\frac{21 mmol H_{2}}{1 mmol {({NH}_{4})}_{2} B_{10} H_{10}}) (\frac{2.0158 mg H_{2}}{1 mmol H_{2}}) = 1.40 mg H_{2}$
The total hydrogen yield is 4.26+1.40=5.66 milligrams, or 5.6% by weight. The ⁺IC:B ratio can also be calculated as follows: $\begin{matrix} 5 mg {({NH}_{4})}_{2} B_{10} H_{10} \\ (\frac{1 mmol {({NH}_{4})}_{2} B_{10} H_{10}}{154.26 mg {({NH}_{4})}_{2} B_{10} H_{10}}) \\ (\frac{10 mmol B}{1 mmol {({NH}_{4})}_{2} B_{10} H_{10}}) \end{matrix} = 0.324 mmol B$ $from ({NH}_{4}) B_{10} H_{10}$ $\begin{matrix} 20 mg {NaBH}_{4} \\ (\frac{1 mmol {NaBH}_{4}}{37.83 mg {NaBH}_{4}}) \\ (\frac{1 mmol B}{1 mmol {NaBH}_{4}}) \end{matrix} = 0.529 mmol B from {NaBH}_{4}$ $\begin{matrix} \begin{matrix} 5 mg {({NH}_{4})}_{2} B_{10} H_{10} \\ (\frac{1 mmol {({NH}_{4})}_{2} B_{10} H_{10}}{154.26 mg {({NH}_{4})}_{2} B_{10} H_{10}}) \end{matrix} \\ (\frac{2 mmol {NH}_{4}^{+}}{1 mmol {({NH}_{4})}_{2} B_{10} H_{10}}) \\ (\frac{1 {mmol}^{+} IC}{1 mmol {NH}_{4}^{+}}) \end{matrix} = 0.0648 {mmol}^{+} IC$ $from {({NH}_{4})}_{2} B_{10} H_{10}$ $\begin{matrix} \begin{matrix} \begin{matrix} 20 mg {NaBH}_{4} \\ (\frac{1 mmol {NaBH}_{4}}{37.83 mg {NaBH}_{4}}) \end{matrix} \\ (\frac{1 mmol {Na}^{+}}{1 mmol {NaBH}_{4}}) \end{matrix} \\ (\frac{1 {mmol}^{+} IC}{1 mmol {Na}^{+}}) \end{matrix} = 0.529 {mmol}^{+} IC from {NaBH}_{4} (\frac{0.529 + 0.0648 {mmol}^{+} IC}{0.529 + 0.324 mmol B}) = {0.70}^{+} IC : B$
Therefore this is equivalent to a fuel blend with a Na:B mole ratio of 0.70.

EXAMPLE 10

7.4 wt-% Hydrogen, ⁺IC/B Ratio=0.38
According to the procedure of Example 9, sodium borohydride (17 g), the hydronium salt of B₁₂H₁₂ ⁻²(11 g), sodium hydroxide (3 g), and water (70 g) were combined to generate hydrogen. This mixture is equivalent to a fuel blend with an ⁺IC to boron ratio of 0.38 and capable of delivering 7.4 wt-% hydrogen. Each mole of sodium borohydride yields four moles of hydrogen according to the equation (1)
NaBH₄+2H₂O→NaBO₂+4H₂ (1)
And each mole of H₂B₁₂H₁₂yields twenty-five moles of hydrogen according to equation (8)
H₂B₁₂H₁₂+18H₂O→6B₂O₃+25H₂ (8)
The hydrogen storage capacity of this blend is determined by calculating the total number of moles of H₂produced and divided by the initial weight of the blend. $\begin{matrix} 17 g {NaBH}_{4} (\frac{1 mol {NaBH}_{4}}{37.83 g {NaBH}_{4}}) \\ (\frac{4 mol H_{2}}{1 mol {NaBH}_{4}}) (\frac{2.0158 g H_{2}}{1 mol H_{2}}) \end{matrix} = 3.62 g H_{2} from {NaBH}_{4}$ $\begin{matrix} 11 g H_{2} B_{12} H_{12} (\frac{1 mol H_{2} B_{12} H_{12}}{143.84 g H_{2} B_{12} H_{12}}) \\ (\frac{25 mol H_{2}}{1 mol H_{2} B_{12} H_{12}}) (\frac{2.0158 g H_{2}}{1 mol H_{2}}) \end{matrix} = 3.85 g H_{2}$ $from H_{2} B_{12} H_{12}$
The total hydrogen yield is 3.62+3.85=7.47 grams, or 7.4% by weight. The ⁺IC:B ratio can also be calculated as follows: $\begin{matrix} 11 g H_{2} B_{12} H_{12} \\ (\frac{1 mol H_{2} B_{12} H_{12}}{143.84 g H_{2} B_{12} H_{12}}) \\ (\frac{12 mol B}{1 mol H_{2} B_{12} H_{12}}) \end{matrix} = 0.918 mol B from H_{2} B_{12} H_{12}$ $\begin{matrix} 17 g {NaBH}_{4} (\frac{1 mol {NaBH}_{4}}{37.83 g {NaBH}_{4}}) \\ (\frac{1 mol B}{1 mol {NaBH}_{4}}) \end{matrix} = 0.449 mol B from {NaBH}_{4}$ $\begin{matrix} 3 g NaOH (\frac{1 mol NaOH}{40.00 g NaOH}) \\ (\frac{1 mol {Na}^{+}}{1 mol NaOH}) (\frac{1 {mol}^{+} IC}{1 mol {Na}^{+}}) \end{matrix} = 0.075 {mol}^{+} IC from NaOH$ $\begin{matrix} 17 g {NaBH}_{4} (\frac{1 mol {NaBH}_{4}}{37.83 g {NaBH}_{4}}) \\ (\frac{1 mol {Na}^{+}}{1 mol {NaBH}_{4}}) (\frac{1 {mol}^{+} IC}{1 mol {Na}^{+}}) \end{matrix} = 0.449 {mol}^{+} IC from {NaBH}_{4} (\frac{0.449 + 0.075 {mol}^{+} IC}{0.449 + 0.918 mol B}) = {0.38}^{+} IC : B$
Therefore this is equivalent to a fuel blend with a Na:B mole ratio of 0.38.

Claims

1. An aqueous fuel for a hydrogen generator comprising an aqueous or hydroalcoholic solution or slurry of a mixture of boron hydrides including at least one boron hydride salt with a positive ion selected from the group consisting of alkali metal, alkaline earth metal and aluminum cations, said 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.

2. An aqueous fuel in accordance with claim 1, wherein said mixture of boron hydrides has a positive ionic charge (⁺IC) to boron ratio of between 0.2 and 0.3 or between 0.7 and 0.8.

3. An aqueous fuel in accordance with claim 1, wherein said boron hydrides are selected from the group consisting of borohydride salts (MBH₄), triborohydride salts (MB₃H₈), decahydrodecaborate salts (M₂B₁₀H₁₀), tridecahydrodecaborate salts (MB₁₀H₁₃), dodecahydrododecaborate salts (M₂B₁₂H₁₂), octadecahydroicosaborate salts (M₂B₂₀H₁₈), and decaborane(14) (B₁₀H₁₄), wherein M is selected from the group consisting of alkali metal, alkaline earth metal and aluminum cations.

4. An aqueous fuel in accordance with claim 1, wherein said mixture contains a borohydride salt with a positive ion selected from the group consisting of sodium, lithium and potassium cations.

5. An aqueous fuel in accordance with claim 4, wherein said mixture additionally contains a stabilizer for said borohydride salt in aqueous media, said stabilizer comprising a hydroxide selected from the group consisting of the hydroxides of sodium, lithium and potassium.

6. An aqueous fuel in accordance with claim 5, wherein said borohydride salt is sodium borohydride and said stabilizer is sodium hydroxide.

7. An aqueous fuel in accordance with claim 3, wherein said boron hydride mixture comprises a borohydride salt and decaborane, said fuel also containing a stabilizer for said borohydride salt in aqueous media, said stabilizer comprising a hydroxide selected from the group consisting of the hydroxides of sodium, lithium and potassium.

8. An aqueous fuel in accordance with claim 7, wherein said boron hydride mixture comprises sodium borohydride and decaborane, and said stabilizer is sodium hydroxide.

9. An aqueous fuel in accordance with claim 3, wherein said boron hydride mixture comprises a triborohydride salt and a dodecahydrododecaborate salt.

10. An aqueous fuel in accordance with claim 9, wherein said triborohydride salt is potassium triborohydride and said dodecahydrododecaborate salt is magnesium dodecahydrododecaborate.

11. An aqueous fuel in accordance with claim 3, wherein said boron hydride mixture comprises a borohydride salt and a dodecahydrododecaborate salt, said fuel also containing a stabilizer for said borohydride salt in aqueous media, said stabilizer comprising a hydroxide selected from the group consisting of the hydroxides of sodium, lithium and potassium.

12. An aqueous fuel in accordance with claim 11, wherein said boron hydride salt is sodium borohydride, said dodecahydrododecaborate salt is sodium dodecahydrododecaborate, and said stabilizer is sodium hydroxide.

13. An aqueous fuel in accordance with claim 3, wherein said boron hydride mixture is a borohydride salt and a triborohydride salt, said fuel also containing a stabilizer for said borohydride salt in aqueous media, said stabilizer comprising a hydroxide selected from the group consisting of the hydroxides of sodium, lithium and potassium.

14. An aqueous fuel in accordance with claim 13, wherein said borohydride salt is sodium borohydride, said triborohydride salt is sodium triborohydride, and said stabilizer is sodium hydroxide.

15. A method of generating hydrogen gas comprising contacting an aqueous fuel comprising an aqueous or hydroalcoholic solution or slurry of a mixture of boron hydrides including at least one boron hydride salt with a positive ion selected from the group consisting of alkali metal, alkaline earth metal, and aluminum cations, said 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 with a hydrogen generating catalyst selected from the group consisting of acids and transition metals.

16. A method of generating hydrogen gas in accordance with claim 15, wherein said mixture of boron hydrides has a positive ionic charge (⁺IC) to boron ratio of between 0.2 and 0.3 or between 0.7 and 0.8.

17. A method of generating hydrogen gas in accordance with claim 15, wherein said boron hydrides are selected from the group consisting of borohydride salts (MBH₄), triborohydride salts (MB₃H₈), decahydrodecaborate salts (M₂B₁₀H₁₀), tridecahydrodecaborate salts (MB₁₀H₁₃), dodecahydrododecaborate salts (M₂B₁₂H₁₂), octadecahydroicosaborate salts (M₂B₂₀H₁₈), and decaborane(14) (B₁₀H₁₄), wherein M is selected from the group consisting of alkali metal, alkaline earth metal and aluminum cations.

18. A method of generating hydrogen gas in accordance with claim 15, wherein said mixture contains a borohydride salt wherein M is selected from the group consisting of sodium, lithium and potassium.

19. A method of generating hydrogen gas in accordance with claim 18, wherein said mixture additionally contains a stabilizer for said borohydride salt in aqueous media, said stabilizer comprising a hydroxide of sodium, lithium and potassium.

20. A method of generating hydrogen gas in accordance with claim 15, wherein the catalyst is an acid selected from the group consisting of hydrochloric acid, sulfuric acid, and phosphoric acid.

21. A method of generating hydrogen gas in accordance with claim 1, wherein the catalyst comprises one or more transition metals selected from the metal families of nickel, cobalt and iron.

22. A method of generating hydrogen gas in accordance with claim 21, wherein the catalyst is ruthenium, cobalt or mixtures thereof.

23. A hydrogen generation system, comprising

(a) an aqueous fuel comprising an aqueous or hydroalcoholic solution or slurry of a mixture of boron hydrides including at least one boron hydride salt with a positive ion selected from the group consisting of alkali metal, alkaline earth metal and aluminum cations, said 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;

(b) a hydrogen generating catalyst selected from the group consisting of acids and transition metals, and

(c) means to contact the aqueous fuel with the catalyst thereby generating hydrogen.

24. A method of generating hydrogen gas in accordance with claim 23, wherein said mixture of boron hydrides has a positive ionic charge (⁺IC) to boron ratio of between 0.2 and 0.3 or between 0.7 and 0.8.

25. A hydrogen generation system in accordance with claim 23, wherein said boron hydrides are selected from the group consisting of borohydride salts (MBH₄), triborohydride salts (MB₃H₈), decahydrodecaborate salts (M₂B₁₀H₁₀), tridecahydrodecaborate salts (MB₁₀H₁₃), dodecahydrododecaborate salts (M₂B₁₂H₁₂), octadecahydroicosaborate salts (M₂B₂₀H₁₈), and decaborane(14) (B₁₀H₁₄), wherein M is selected from the group consisting of alkali metal, alkaline earth metal and aluminum cations.

26. A hydrogen generation system in accordance with claim 23, wherein said mixture contains a borohydride salt with a positive ion selected from the group consisting of sodium, lithium and potassium cations.

27. A hydrogen generation system in accordance with claim 23, wherein the hydrogen generating catalyst is an acid selected from the group consisting of hydrochloric acid, sulfuric acid, and phosphoric acid, and said acid and the aqueous fuel are stored in separate containers.

28. A hydrogen generation system in accordance with claim 23, wherein the hydrogen generating catalyst comprises a substrate having molecules of a transition metal bound thereto, entrapped within, and/or coated thereon and said means to contact comprises a containment system for said catalyst whereby the catalyst can be moved into and out of contact with the aqueous fuel.

29. A hydrogen generation system in accordance with claim 23, additionally containing a gas-liquid separator to separate hydrogen from the effluent thereof.

30. A hydrogen generation system in accordance with claim 23, wherein at least a portion of the water in said aqueous fuel is obtained from the reaction product of a hydrogen-consuming device, said device being operably connected with said system.

31. A hydrogen generation system in accordance with claim 30, wherein the hydrogen-consuming device is selected from the group consisting of a fuel cell, a combustion engine, a gas turbine, and combinations thereof.

32. A hydrogen generation system, comprising

(a) a fuel blend including at least one boron hydride salt with a positive ion selected from the group consisting of alkali metal, alkaline earth metal, and aluminum cations;

(b) an accelerant comprising an acidic polyhedral boron hydride salts selected from the group consisting of the hydronium and ammonium salts of polyhedral boron hydrides, wherein said mixture of boron hydrides and accelerant has a positive ionic charge (⁺IC) to boron ratio of between 0.2 and 0.4 or between 0.6 and 0.99; and

(c) means to contact the fuel blend and water with the accelerant thereby generating hydrogen.

33. A method of generating hydrogen gas in accordance with claim 32, wherein said mixture of boron hydrides and accelerant has a positive ionic charge (⁺IC) to boron ratio of between 0.2 and 0.3 or between 0.7 and 0.8.

34. A hydrogen generation system in accordance with claim 35, wherein said boron hydrides are selected from the group consisting of borohydride salts (MBH₄), triborohydride salts (MB₃H₈), decahydrodecaborate salts (M₂B₁₀H₁₀), tridecahydrodecaborate salts (MB₁₀H₁₃), dodecahydrododecaborate salts (M₂B₁₀H₁₂), octadecahydroicosaborate salts (M₂B₂₀H₁₈), and decaborane(14) (B₁₀H₁₄), wherein M is selected from the group consisting of alkali metal, alkaline earth metal and aluminum cations.

35. A hydrogen generation system in accordance with claim 32, wherein said accelerant is H₂B₁₂H₁₂.

36. A hydrogen generation system in accordance with claim 32, wherein said accelerant is (NH₄)₂B₁₀H₁₀.

37. A hydrogen generation system in accordance with claim 32, wherein said mixture contains a borohydride salt wherein the positive ion is selected from the group consisting of sodium, lithium and potassium.

38. A hydrogen generation system in accordance with claim 32, wherein at least a portion of the water is obtained from the reaction product of a hydrogen-consuming device, said device being operably connected with said system.

39. A hydrogen generation system in accordance with claim 38, wherein the hydrogen-consuming device is selected from the group consisting of a fuel cell, a combustion engine, a gas turbine, and combinations thereof.