Patent Application
20240072279
This application claims priority of German patent application no. 10 2022 121 458.3, filed Aug. 25, 2022, the entire content of which is incorporated herein by reference.
The present disclosure relates to a hydrogen storage assembly which makes it possible for example to store hydrogen in a fuel cell system provided for producing electrical energy in a vehicle.
In hydrogen storage assemblies utilized for example in vehicles to provide hydrogen for the fuel cell process in a fuel cell system, the hydrogen is stored at very low temperatures of below −250° C. in the liquid state of matter in at least one hydrogen tank. Due to heat input which is unavoidable despite very good insulation, lack of use of such a fuel cell system for a prolonged period results in the formation of gaseous hydrogen in such hydrogen tanks, generally also known as cryotanks, thus leading to a pressure increase which requires controlled release in procedures performed on a cyclic basis for example to avoid an excessively high pressure increase in such a hydrogen tank above a value of about 20 bar for example.
It is an object of the present disclosure to provide a hydrogen storage assembly, in particular fora fuel cell system in a vehicle, in which the release of excessively highly concentrated gaseous hydrogen to the environment can be avoided.
This object is achieved according to the disclosure by a hydrogen storage assembly, in particular for a fuel cell system in a vehicle, including at least one hydrogen tank for storage of liquid hydrogen and at least one hydrogen sorption/catalyst unit for sorption and catalytic conversion of gaseous hydrogen released from the at least one hydrogen tank.
The hydrogen storage assembly constructed according to the disclosure utilizes two processes to avoid the release of excessively concentrated gaseous hydrogen to the environment. It firstly utilizes a sorption process in which, when gaseous hydrogen is released from the at least one hydrogen tank and is not reacted in a fuel cell to produce electrical energy, the hydrogen is temporarily sorbed. The sorbed hydrogen or at least a substantial portion thereof may subsequently be oxidized in a catalytic process and for example reacted with atmospheric oxygen to form water. The hydrogen storage assembly according to the disclosure can utilize the energy liberated in the form of heat in the sorption process to increase the temperature of the hydrogen sorption/catalyst unit to a temperature in the range of or above the reaction temperature of the catalytic process. The sorption of hydrogen can thus activate the catalytic process which itself also liberates energy, thus making it possible, without external supply of energy, to react the gaseous hydrogen released from the at least one hydrogen tank and to avoid the release from the at least one hydrogen tank of highly concentrated hydrogen which is thus potentially critical in terms of explosion risk in the release of gaseous hydrogen.
In order to be able to provide a sufficiently large surface area for the sorption and catalytic reaction of hydrogen it is proposed that the at least one hydrogen sorption/catalyst unit includes at least one substrate around which gaseous hydrogen can flow, wherein hydrogen sorption material and hydrogen catalyst material are provided at the substrate.
The at least one substrate may be constructed with ceramic material for example and/or the at least one substrate may include a multiplicity of flow channels through which gaseous hydrogen can flow. This substrate may in particular have a honeycomb structure having a plurality of substantially linearly extending flow channels. In an alternative embodiment the substrate may be in the form of a porous body, so that the flow channels are formed in the porous structure of the substrate.
For interaction with the gaseous hydrogen released from the at least one hydrogen tank the at least one substrate may include the hydrogen sorption material and the hydrogen catalyst material on its surface defining the flow channels.
To achieve this at least a portion of a substrate surface of the at least one substrate may be coated with the hydrogen sorption material and the hydrogen catalyst material may be provided on at least one surface of the hydrogen sorption material.
In order to be able to rapidly activate the catalytic process to be performed for reaction of the hydrogen especially even at very low ambient temperatures it is proposed that a heating unit is assigned to the at least one substrate. The heating unit may be electrically energizable to provide heat.
In an advantageous embodiment the at least one hydrogen sorption/catalyst unit may be configured for adsorption of hydrogen.
In order to be able to utilize the process of physical incorporation of hydrogen into the lattice structure of the hydrogen sorption material it is proposed that the hydrogen sorption material includes physisorption material. As a material particularly suitable for the incorporation of hydrogen the physisorption material may include zeolite.
In order in an alternative embodiment to be able to utilize the process of chemical adsorption of hydrogen onto the hydrogen sorption material the hydrogen sorption material may include chemisorption material. To this end the chemisorption material may for example include a metal hydride-forming metal, for example lithium, a mixture of lithium and aluminum or a mixture of sodium and boron.
The at least one hydrogen sorption/catalyst unit may be configured for catalytic oxidation of hydrogen. To this end the hydrogen catalyst material may include palladium and/or platinum.
The disclosure further relates to a fuel cell system, in particular for a vehicle, including at least one fuel cell and a hydrogen storage assembly constructed according to the disclosure for supplying gaseous hydrogen to an anode region of the at least one fuel cell.
The invention will now be described with reference to the drawings wherein:
A fuel cell system 10 shown in
The fuel cell system 10 shown in
In the hydrogen tank 18 the hydrogen required for the fuel cell process is stored at very low temperature in the liquid state of matter. After a prolonged period of downtime of the fuel cell system 12 gaseous hydrogen requiring discharging from the hydrogen tank 18 may be formed above the liquid hydrogen in the interior of the hydrogen tank 18. To blow off gaseous hydrogen H from the hydrogen tank 18 the valve assembly 24 passes the gaseous hydrogen H to the hydrogen sorption/catalyst unit 22. As shown schematically in
At its surface defining the flow channels 32 the ceramic material 28 of the substrate 30 is coated at least in some regions with hydrogen sorption material 34. Hydrogen catalyst material 36 is provided at/incorporated into the surface of the hydrogen sorption material 34. The hydrogen sorption material serves to bind the gaseous hydrogen H introduced into the flow channels 32 by adsorption at the substrate 30, so that in particular at commencement of such a process for releasing gaseous hydrogen from the hydrogen tank 18 no highly concentrated hydrogen gas is emitted to the environment via the hydrogen sorption/catalyst unit 22. The hydrogen catalyst material 36 with which the hydrogen sorption material 34 is doped serves to oxidize the gaseous hydrogen H in the catalytic process and for example effect reaction thereof with atmospheric oxygen to form water.
The adsorption of hydrogen at the hydrogen sorption material liberates energy in the form of heat. This energy liberated in the form of heat has the result that the hydrogen catalyst material 36 provided at/incorporated into the hydrogen sorption material 34 is heated and brought to a temperature in the range of/above the reaction temperature at which the catalytically induced oxidation of hydrogen proceeds and which may have a value of about 100° C. or below. Further hydrogen H introduced into the substrate 30 is thus catalytically reacted so that a hydrogen-depleted and for example water/steam-containing gas G is released from the hydrogen sorption/catalyst unit 22. Similarly to the fuel cell exhaust gas, this hydrogen-depleted gas G may for example be introduced into the fuel cell exhaust gas apparatus 20 in order to separate water/steam therefrom and thus release a gas substantially freed of water and steam to the environment.
The catalytic reaction of hydrogen started by the energy liberated in the adsorption process likewise liberates energy in the form of heat which results in further heating of not only the hydrogen catalyst material 36 but also the hydrogen sorption material 34. Especially through the heating of the hydrogen sorption material 34, hydrogen sorbed in/on the material is liberated again and for example converted into water in the already occurring catalytic reaction.
The incorporation/sorption of hydrogen described above and the catalytic reaction of hydrogen makes it possible to ensure that a gas G released to the environment contains only a small amount/concentration of hydrogen, thus avoiding the potential risk of ignition/explosion of excessively hydrogen-enriched gas. The energy liberated in the adsorption process and also in the catalytic reaction simultaneously ensures that the process for reacting hydrogen, which brings about the reduction in the hydrogen concentration, is activated and independently maintained even at low ambient temperatures of for example below 0° C. Since, at the same time, even the hydrogen sorbed at commencement of the process is desorbed again and catalytically reacted in this process the hydrogen sorption/catalyst unit 22 is regenerated during the process and is available for a further release cycle after the process has ended.
The adsorption of hydrogen at the hydrogen sorption material 34 may utilize various processes. The hydrogen sorption material 34 may for example include physisorption material in which the hydrogen is incorporated in the lattice structure of the physisorption material. Zeolite for example may be used as a material particularly suitable for the incorporation of hydrogen. In an alternative process/an alternative embodiment the hydrogen sorption material 34 may include chemisorption material in which the hydrogen is sorbed by a chemical reaction. Such a chemisorption material may for example include metal, for example lithium, a mixture of lithium and aluminum or a mixture of sodium and boron.
Each of these adsorption processes liberates heat and input of heat into the hydrogen sorption material 34 allows hydrogen bonded thereto as sorptive to be liberated again and then reacted/oxidized over the hydrogen catalyst material 36. Such hydrogen catalyst material 36 may include palladium and/or platinum.
It should finally be noted that various variations may be undertaken in the case of a hydrogen storage assembly 40 constructed according to the disclosure which includes as essential constituents one or more hydrogen tanks 18 and one or more hydrogen sorption/catalyst units 22. Accordingly, for example, the substrate 30 may have a different structure, for example a porous structure, and thus provide a multiplicity of intertwined/interconnected flow channels. The hydrogen-depleted gas G released from such a hydrogen sorption/catalyst unit 22 may also be released directly to the environment and not into a fuel cell offgas apparatus. It should further be emphasized that the hydrogen storage assembly 40 constructed according to the disclosure may find use not only in connection with a fuel cell system, in particular in a vehicle. Other, especially also stationary, apparatuses too can utilize such a hydrogen storage assembly 40 which provides for the possibility of repeatedly releasing gaseous hydrogen from one or more hydrogen tanks 18 and of releasing a hydrogen-depleted gas to the environment by way of the above-described process.
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 121 458.3 | Aug 2022 | DE | national |
