Solid compositions generating hydrogen by combustion, comprising an alkali metal borohydride and an ammonium salt

Abstract

The invention relates to solid compositions that can decompose generating hydrogen in a self-sustaining combustion reaction after this reaction has been initiated by an appropriate heat source. These compositions comprise an alkali metal borohydride and an oxidizing mineral ammonium salt of formula NH 4 Y, in which Y represents a group consisting only of nitrogen and oxygen. The ratio of the weight content of alkali metal borohydride to the weight content of the salt of general formula NH 4 Y is between 1 and 4. Thus, high hydrogen mass yields are obtained, of around 8 to 14%, thereby making it possible to reduce the size and the weight of the hydrogen generators used in certain systems, especially in proton exchange membrane fuel cells.

1 . Solid composition that can decompose generating hydrogen in a self-sustaining combustion reaction after this reaction has been initiated by an appropriate heat source, the said composition comprising an alkali metal borohydride and an oxidizing mineral ammonium salt, characterized in that the said salt satisfies the general formula NH 4 Y in which Y represents a group consisting only of nitrogen and oxygen, and in that the ratio of the weight content of alkali metal borohydride to the weight content of the salt of general formula NH 4 Y is between 1 and 4.  
     
     
         2 . Solid composition according to  claim 1 , characterized in that Y represents the nitrate or dinitramide group.  
     
     
         3 . Solid composition according to  claim 1 , characterized in that it is in the form of a compact material  
     
     
         4 . Solid composition according to  claim 3 , characterized in that the compact material is a pellet or a particle.  
     
     
         5 . Solid composition according to  claim 1 , characterized in that it contains no organic matter.  
     
     
         6 . Solid composition according to  claim 1 , characterized in that it essentially consists of an alkali metal borohydride and a salt of general formula NH 4 Y.  
     
     
         7 . Solid composition according to  claim 1 , characterized in that the sum of the weight contents of alkali metal borohydride and of the salt of general formula NH 4 Y is greater than or equal to 90% compared with the total weight of the composition.  
     
     
         8 . Solid composition according to  claim 1 , characterized in that the alkali metal borohydride is chosen from the group consisting of lithium borohydride, sodium borohydride and mixtures thereof.  
     
     
         9 . Process for generating hydrogen by self-sustaining combustion of a solid composition comprising an alkali metal borohydride and an oxidizing mineral ammonium salt, characterized in that: 
 a homogenous, pulverulent or granular, solid composition comprising an alkali metal borohydride and an ammonium salt of general formula NH 4 Y, in which Y represents a group consisting only of nitrogen and oxygen, the ratio of the weight content of alkali metal borohydride to the weight content of the salt of general formula NH 4 Y being between 1 and 4, is produced;    next, this composition is agglomerated using appropriate means so as to form a compact material;    the compact material is placed in a combustion chamber; and    the combustion of the compact material is initiated using an appropriate heat source, which causes the self-sustaining combustion of the material with generation of hydrogen until the end of combustion.    
     
     
         10 . Hydrogen generator intended to supply a proton exchange membrane fuel cell with hydrogen, characterized in that this generator is a pyrotechnic generator comprising a solid composition according to  claim 1 .  
     
     
         11 . Proton exchange membrane fuel cell using hydrogen as fuel, comprising at least one electrochemical cell and a hydrogen generator connected to the anode compartment of the electrochemical cell, characterized in that this hydrogen generator is a pyrotechnic generator according to  claim 10.