Technical field

The present invention relates to a hydrogen generator particularly for supplying fuel cells and the like.

Background art

A hydrogen supply is preferable for the operation of fuel cells and of other electrochemical, endothermic and/or chemical devices.

The fact that hydrogen is a highly abundant element leads to the presumption that it is relatively simple to provide: in theory, its extraction from water appears straightforward.

Actually, extraction is an expensive and complicated process; the cheapest way to produce this element is to use petroleum or other fossil fuels. Almost all produced hydrogen is in fact obtained from fossil fuels.

The most common industrial path for producing it is in any case the one that uses the technique known as "steam reforming" of natural gas and provides, in a first step, for the elimination of the sulfurous compounds that are present in the hydrocarbon (for the sake of convenience, reference shall be made to CH ₄ in indicating the reactions).

Subsequently, in the so-called "primary reforming" step, methane reacts with water vapor, according to the formula:

CH ₄ + H ₂ O→CO + 3H ₂

At this point, a postcombustion with air occurs (this is called the "secondary reforming" step), followed by a conversion reaction described by the following formula:

CO + H ₂ →CO ₂ + H ₂

This method then provides for the final steps of elimination of the residual carbon dioxide and carbon monoxide.

In more general terms, energy is required to produce hydrogen: to extract it from water by electrolysis, for example, electric power must be available. For this reason, hydrogen is not an energy source, but rather a medium for carrying and storing available energy (i.e., a vector).

The extraction of hydrogen by means of chemical processes is in practice particularly interesting, since it makes it possible to reduce energy costs with respect to known industrial processes.

One chemical process for hydrogen extraction is based on sodium borohydride (chemical formula NaBH ₄ ): this substance is generally unstable if it is not dispersed in a solution and at ambient temperature it is solid, generally in powder form.

Sodium borohydride is a selective reducing reagent used especially in the production of drugs, intermediates and fine chemistry products.

It is used in small-scale fuel cells as a means for storing hydrogen. Hydrogen can be produced by decomposition of the aqueous solution and sent to a hydrogen cell, or the sodium borohydride can be decomposed directly in the cell itself according to the following reaction:

NaBH ₄ →8 OH-→ NaBO ₂ + 6 H ₂ O + 8 e-

S odium borate can subsequently be recovered in order to regenerate the borohydride, making the process potentially useful for rechargeable fuel cells.

The production of hydrogen is based on the following reaction:

NaBH ₄ + 2 H ₂ O -> NaBO ₂ + 4 H ₂ + heat

These chemical methods, aimed at supplying fuel cells or other user devices, require continuous stoichiometric dosages (additions of further doses of the reagents are performed on the basis of feedback processes that check if the reaction is kept at an optimum productivity level), and this is particularly difficult, because the control and management means require a very complex circuit architecture that is accordingly easily subject to failures.

Disclosure of the invention

The aim of the present invention is to solve the drawbacks described above, by providing a hydrogen generator particularly for supplying fuel cells and the like that is based on a chemical reaction of hydrogen extraction and suitable for the automatic dosage of the produced quantity of hydrogen.

Within this aim, an object of the invention is to propose a fuel cell that is supplied by means of a hydrogen generator with automatic control of the quantity of hydrogen produced by means of the chemical extraction reaction.

Another object of the present invention is to provide a hydrogen generator particularly for supplying fuel cells and the like that has low costs, is relatively simple to provide in practice and safe in application.

This aim and these objects, as well as others that will become better apparent hereinafter, are achieved by a hydrogen generator particularly for supplying fuel cells and the like, by hydrolysis of a reagent, characterized in that it comprises a tank for the reagent, a duct for introducing the reagent in a closed reaction container, and a discharge unit for the controlled outflow of hydrogen from said container, said reaction container comprising a reaction catalyst that can move automatically from a first configuration, in which it is kept at least partially immersed in the reagent to produce hydrogen, to a second configuration, in which said catalyst is spaced from the reagent in order to interrupt the production of hydrogen, and vice versa. Brief description of the drawings

Further characteristics and advantages of the invention will become better apparent from the detailed description that follows of a preferred but not exclusive embodiment of the hydrogen generator according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a schematic front elevation view of the hydrogen generator according to the invention;

Figure 2 is a hydraulic diagram of the hydrogen generator according to the invention, connected to a user device. Ways of carrying out the invention

With reference to the figures, a hydrogen generator according to the invention, generally designated by the reference numeral 1, is particularly suitable for the supply of fuel cells A and the like by means of the hydrolysis of a reagent B.

It should be specified immediately that the use of the generator 1 to supply fuel cells A is a preferred application (and will be referenced constantly hereinafter) but not the exclusive application of the invention; other different applications, aimed at supplying different devices, where the specific requirements allow it and/or make it preferable, are in fact provided.

According to the invention, the generator 1 comprises a tank 2 for the reagent B and a duct 3 for introducing the reagent B within a closed reaction container 4, inside which, by means of the above cited hydrolysis, gaseous hydrogen adapted to supply the fuel cell A is produced.

In order to send the hydrogen to the cell A, the generator 1 comprises a discharge unit 5 for the controlled outflow of said hydrogen from the container 4.

The container 4 further comprises a reaction catalyst 6, which can move automatically from a first configuration, in which it is kept at least partially immersed in the reagent B for achieving the production of hydrogen by hydrolysis (which is activated indeed by the catalyst 6), to a second inactive configuration and vice versa. In the second configuration, the catalyst 6 is spaced from the reagent B in order to interrupt the production of hydrogen.

It is useful to specify immediately that according to the preferred embodiment, the first configuration introduced above corresponds to an only partial immersion of the catalyst 6 in the reagent B, and transition from the first configuration to the second configuration and vice versa occurs during the normal operation of the generator 1. This condition of normal operation therefore provides for the possibility of self-regulation of the quantity of hydrogen that is produced and ends by way of the action of the operator or by simple depletion of the reagent B in the container.

According to the preferred embodiment, as will become better apparent hereinafter, a third configuration is therefore also provided in which the catalyst 6 is fully immersed in the reagent B and which occurs during the steps for loading the reagent B in the container 4 and upon depletion of the reagent B in the container 4. The transition to the third configuration, like the other transitions, is also automatic.

Advantageously, the hydrogen generator 1 comprises automatic means 7 for moving the catalyst 6 in order to produce transition from the first configuration to the second configuration and vice versa.

The possibility of automatic movement of the catalyst 6 (optionally by way of the movement means 7) from the first configuration to the second configuration and vice versa makes it possible, as will become better apparent hereinafter, to interrupt automatically the hydrolysis reaction once the quantity of hydrogen that has been produced has reached a value that is defined in dependence on the requirements of the cell A (or of the other user device to which the container 4 is connected), thereby achieving the intended aim and objects.

More specifically, the movement means 7 comprise a shaft 8, which can perform a translational motion hermetically within the container 4: the shaft 8 is jointly connected to the catalyst 6 and is actuated from the outside of the container 4.

Moreover, the movement means 7 comprise an elastic member 9, which is associated with the shaft 8 and designed for the application of an elastic reaction that is directed toward the bottom 4a of the container 4 in order to keep the catalyst 6, coupled to the lower end 8a of the shaft 8, in at least partially immersed conditions, which as mentioned above correspond to the first configuration (and to the third one).

Conveniently, the container 4 is closed hermetically in an upper region by a first elastically deformable membrane 10, which is coupled to the shaft 8: the increase in pressure inside the container 4 caused by the release of gaseous substances, as a consequence of the reaction, produces an expansion (swelling) of the first membrane 10, as shown in Figure 1. It should in fact be specified that in Figure 1 a solid line indicates the first membrane 10 when it is not deformed and a broken line indicates the first membrane 10 when it is expanded as a consequence of the increase in pressure.

The expansion pushes upward the shaft 8, which can thus overcome the above cited elastic reaction and perform a translational motion, rising and moving the catalyst 6 so that it emerges completely from the reagent B for transition from the first configuration to the second configuration.

Subsequently, the consequent pressure decrease (due to the outflow of the produced hydrogen toward the cell A) produces transition from the second configuration to the first configuration (and therefore the restart of the hydrolysis reaction).

Conveniently, the elastic member 9 substantially consists of a spring 11 : the preloading of the spring 11 is adjustable for varying the intensity of the elastic reaction that can be produced, and this makes it possible to predefine at will the value of the pressure that is adapted to determine transition from the first configuration to the second configuration.

According to a first possible embodiment, the discharge unit 5 can consist of a tube that is connected to the container 4 and leads to the load cell A.

Conveniently, the hydrogen generator 1 comprises an apparatus for filtering and purifying the gaseous hydrogen.

More particularly, according to an embodiment of substantial practical interest, the apparatus consists substantially of a second membrane, which is interposed between the free surface of the reagent B and the discharge unit 5. Such second membrane is capable of retaining water and any other liquid particles contained in the gaseous substances released during the reaction.

In order to achieve the intended aim, the second membrane is substantially made of a polymeric material, preferably of the type of fluoropolymers, and is for example hydrophobic, in order to thus purify the produced gaseous hydrogen before sending it to the cell A through the discharge unit 5.

It should be noted that the possibility is provided, and within the scope of the appended claims, to provide generators 1 in which the first membrane 10 and the second membrane coincide, thus entrusting to a single component the dual task of hermetic closure of the container 4 and of filtration and purification of the gaseous hydrogen.

It should also be specified that the possibility is not excluded of providing generators 1 that have different types of filtration and purification apparatuses (which are in any case within the scope of the protection of the invention), capable therefore of providing the desired filtration for example by means of molecular sieves, silica gel, activated carbon or even a combination of two or more of the proposed solutions (optionally arranged in series) or of further solutions that are equivalent thereto.

With reference to the reagent B, which inside the container 4 is subjected to a hydrolysis reaction in order to generate gaseous hydrogen, it comprises at least one aqueous solution of a metal hydride.

More particularly, the metal hydride preferably comprises a metal of group IA of the periodic table of the elements, an element of group IIIA of the periodic table of the elements, and hydrogen.

The metal of group IA can for example be chosen among lithium, sodium and potassium; as an alternative, instead of the metal cited above it is possible to use the ammonium ion or an organic group thereof. The element of group IIIA of the periodic table of the elements can be chosen for example among boron, aluminum and gallium.

According to possible embodiments, cited by way of non-limiting example of the application of the invention, the metal hydride comprised in the reagent B has a formulation that is preferably chosen among one of the following: NaBH ₄ , LiBH ₄ , KBH ₄ , NH ₄ BH ₄ , NaAlH ₄ , NaGH ₄ .

Advantageously, the reagent B receives the addition of a stabilizing basic agent, which is capable of keeping a pH value close to 14 and can be chosen preferably among sodium hydroxide, potassium hydroxide and lithium hydroxide (and even more preferably the basic agent consists of sodium hydroxide, because of its high solubility, and it is in any case preferable that it corresponds to the chemical hydride).

According to the preferred but not exclusive embodiment, the catalyst 6 comprises a support 12, which is coupled to the lower end 8a of the shaft 8 and is preferably of a ceramic and monolithic type. The support 12 carries an active member made of a material that is preferably chosen among a transition metal, a boride of a transition metal, a chloride of a transition metal, an alloy that contains a transition metal, a mixture of a transition metal.

In particular, the support 12 is of the type known as honeycomb and by means of the known method of impregnation or of the supercritical CO ₂ method keeps the active member trapped inside it.

For example, the active member can consist of a material chosen among nickel, cobalt, ruthenium, rhodium, palladium, iron, osmium, iridium, platinum, niobium, silver, cobalt chloride, copper chloride, Pt- LiCoO ₄ , Pt-CoO, Pt-TiO ₂ .

The possibility is further provided to trap the active member (and only the active member) in a third membrane comprised within the support 12; said third membrane is capable of retaining the active member and is of the hydrophilic type and therefore permeable to the reagent B. Conveniently, as can be deduced from the accompanying figures, the duct 3 for introducing the reagent B within the closed reaction container 4 is controlled by a bidirectional pump 13 and by a respective first one-way valve 14 for allowing the free passage of the reagent B from the tank 2 to the container 4 and for preventing the passage of the reagent B in the opposite direction.

According to the preferred but not exclusive embodiment, the duct 3 for introducing the reagent B within the closed reaction container 4 comprises a discharge branch 3a, which leads to a respective collection vessel 15 for the liquid C produced by the hydrolysis reaction.

As is particularly evident from the figures, the discharge branch 3 a is arranged upstream of the pump 13 and is intercepted by a second one-way valve 16 for allowing the free passage of the liquid C from the container 4 to the collection vessel 15 and for preventing the passage of the liquid C in the opposite direction.

The fuel cell A according to the invention comprises means for connection to the discharge unit 5, for the outflow of hydrogen from the closed reaction container 4. The container 4 comprises the catalyst 6 of the hydrolysis reaction, which can move from a first configuration, in which it is kept at least partially immersed in the reagent B to produce hydrogen, to a second inactive configuration, and vice versa.

In the second configuration, the catalyst 6 is spaced from the reagent B for interrupting the production of hydrogen.

The functioning of the hydrogen generator according to the invention is as follows.

In order to start the hydrolysis reaction it is sufficient to activate the bidirectional pump 13 so that it sends the reagent B, drawing it from the tank 2, through the duct 3 to the container 4.

As mentioned earlier, in this preliminary step the reagent B is collected within the container 4 in such a quantity as to move the catalyst 6 into the third configuration of full immersion.

The full immersion of the catalyst 6 in the reagent B thus triggers the hydrolysis reaction, with consequent high production of gaseous hydrogen inside the container 4, thus allowing the generator 1 to reach rapidly the pressure conditions that correspond to normal use. The hydrogen passes through the second membrane, being thus filtered to subsequently reach the fuel cell A (or other load connected to the container 4).

Progressively, due to the outflow of the hydrogen and to the consequent pressure drop, the catalyst 6 rises with respect to the level of the reagent B until it reaches conditions of partial immersion (and therefore reaches the first configuration). If the production of hydrogen exceeds the predefined value (for example due to an excessive dose of reagent B introduced in the container 4), the corresponding further pressure increase inside the container 4 produces an expansion of the first membrane 10, which draws upward the shaft 8 and consequently the catalyst 6, overcoming the elastic reaction of the spring 11.

Transition is thus achieved to the second configuration already described, in which the support 12 and the active member are spaced from the reagent B (are raised with respect to it) and the hydrolysis reaction and the production of hydrogen are thus interrupted (since direct contact no longer occurs).

In this second configuration, the excess hydrogen is used up progressively until the previous pressure conditions are restored and therefore the generator 1 according to. the invention is returned to the first configuration, restarting thereby the production of hydrogen.

It is thus evident that the generator 1 can interrupt automatically the hydrolysis reaction in case of an excessive production of hydrogen and can restart it automatically once the excess has been used up.

Once the initial load transient has been passed, it is the alternating transition from the first configuration to the second configuration and vice versa that makes it possible to keep substantially constant the produced quantity of gaseous hydrogen (or otherwise to keep said quantity within a predefined range) even in case of an excessive or otherwise incorrect dosage of the reagent B and of the other elements that take part in the hydrolysis reaction.

In the cell A (or other user device) that is supplied by means of the generator 1 it is therefore possible to ensure automatic control of the quantity of hydrogen used for its supply.

Upon depletion of the reagent B, the low value of the pressure inside the container 4 automatically causes the complete immersion of the catalyst 6 in the reagent B, thus providing the third described configuration. Complete depletion of the reagent B can be followed by a new loading cycle (thus sending new reagent B to the container 4 through the duct 3) or, more simply, it is possible to interrupt the use of the generator 1.

In any case, once the reagent B has been depleted, the liquid C that is accumulated as a waste product of the hydrolysis reaction can be sent, by way of the bidirectional pump 13, to the vessel 15 through the discharge branch 3 a of the duct 3.

It should also be noted that the presence of the first one-way valve 14 and of the second one-way valve 16 avoids the danger that the reagent B or the liquid C might flow through portions of the duct 3 which they are not intended to pass.

During the step of passage of the reagent B to the container 4, the second one-way valve 16 in fact prevents the reagent B from being sent incorrectly also to the vessel 15, while the first one-way valve 14 merely allows drawing the reagent B from the tank 2.

Likewise, during the step for sending the liquid C to the collection vessel 15, it is the first one-way valve 14 that prevents the liquid C from being sent incorrectly to the tank 2 of the reagent B, while the second one- way valve 16 allows discharge of the liquid C into the vessel 15. In practice it has been found that the hydrogen generator according to the invention fully achieves the intended aim, since the resort to a reaction catalyst that can move automatically from a first configuration, in which it is kept at least partially immersed in a reagent contained in a suitable container for the production of hydrogen, to a second configuration, in which the catalyst is spaced from the reagent in order to interrupt the production of hydrogen, and vice versa, ensures the possibility of obtaining gaseous hydrogen by means of a chemical extraction reaction and at the same time makes it possible to dose automatically the produced quantity of hydrogen.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements.

In the exemplary embodiments shown, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other exemplary embodiments.

Moreover, it is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer.

In practice, the materials used, as well as the dimensions, may be any according to requirements and to the state of the art.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.