Container for absorbing hydrogen, method for producing the same and use of a galvanic metal layer

Abstract

The invention relates to a container (1) comprising a cavity (2) for receiving hydrogen, wherein inner sides (6) of walls (3) of the container (1) facing the cavity (2) are formed from steel, and the inner sides (6) of the walls (3) comprise a galvanic metal layer (4) on the steel.

Description

[0001] The invention relates to a container designed to hold hydrogen, as well as a method and a device for producing the container. Furthermore, the invention also encompasses the use of a galvanic metal layer.

[0002] Hydrogen is becoming an increasingly important energy carrier in recent times. This brings with it a number of challenges. Due to the very small molecular size of hydrogen (H2), it is very difficult to store hydrogen in a stable manner over the long term. Hydrogen can also have an embrittlement effect on some materials. Newer hydrogen storage containers are therefore made from carbon fiber composite material, which is at least unreactive towards hydrogen. For reasons of leak-tightness, however, steel would be the more suitable material; however, even here, penetration by hydrogen under high pressures, such as around 700 bar, cannot be completely avoided, and steel can also be subject to embrittlement by hydrogen.

[0003] Based on this prior art, it is therefore an object of the present invention to provide a container for containing hydrogen that is characterized by a high degree of impermeability to hydrogen and is also stable in mechanical, physical, and chemical terms. Furthermore, it is an object of the present invention to provide a method for producing such a container that is easy to implement. Furthermore, it is an object of the present invention to provide an apparatus for carrying out the method for producing a container for containing hydrogen. Furthermore, it is also an object of the present invention to provide a use for a galvanic metal layer.

[0004] The objects are achieved by the subject matter of the independent claims. The subclaims contain advantageous developments and refinements of the invention.

[0005] Accordingly, the problem is solved by a container that comprises a hollow space. The container is not restricted in detail in terms of shape, size, and design. It is essential to the invention that the container comprises a hollow space that is designed to hold hydrogen. The hydrogen can be held by the container permanently or only for a limited time and thus reversibly. The hydrogen can also simply flow through the container and thus only remain there temporarily. The container can thus be designed as a storage container or as a tank and can be filled with hydrogen, whereby the hydrogen can also be removed from the container as needed.

[0006] The cavity of the container is formed by surrounding walls, with the inner sides of the container walls facing the cavity being made of steel. This means that the walls of the cavity are either made entirely of steel or have a two- or multi-layer structure, with the innermost layer facing the cavity being made of steel.

[0007] Steel has the advantage over fiber-reinforced plastics, in particular, of its high mechanical stability and inherently high hydrogen impermeability. Steel is also less susceptible to chemical and physical influences.

[0008] To improve hydrogen resistance, the interior walls of the steel contain a galvanic metal layer. It is known to apply galvanic coatings to the exterior of steel containers. The galvanic coating may also form a barrier layer for hydrogen, but it has the disadvantage that the steel already comes into contact with the hydrogen, thus neither preventing steel embrittlement nor effectively preventing the hydrogen from penetrating the steel, as it has already penetrated the steel before it reaches the galvanic coating.

[0009] According to the invention, the galvanic metal layer applied by galvanization is applied to the inner surfaces of the steel walls surrounding the cavity. This reduces the penetration pressure of the hydrogen, even at high pressures of approximately 700 bar, and also reduces the steel's tendency to embrittlement.

[0010] The container according to the invention is thus characterized by very good hydrogen resistance, high mechanical, physical and chemical stability and very good hydrogen barrier properties and thus high impermeability to hydrogen.

[0011] The hydrogen impermeability can be advantageously improved by having a face-centered cubic lattice structure. Due to their sphere packing, face-centered cubic lattice structures have a high density and no free octahedral vacancies, thus preventing hydrogen penetration particularly effectively.

[0012] The hydrogen barrier properties can be further improved by using nickel as the metal. Nickel is characterized by particularly high hydrogen impermeability and very good resistance to hydrogen, making it the preferred material. Nickel also exhibits no tendency to embrittlement in the presence of hydrogen, which improves the resistance of the container.

[0013] The galvanic nickel layer is formed, in particular, from pure nickel and thus comprises at least 99.9 wt.% nickel based on the total mass of pure nickel. The nickel layer has, in particular, a columnar layer structure and a density of 8.8 g / cm 3 , a melting range of 1435 to 1445 °C and a thermal conductivity of 90 W / mK at room temperature (25 °C).

[0014] The nickel layer has the following mechanical properties, which are measured according to DIN EN 10002: Young's modulus (GPa): 180 to 200 Elongation at break L0 (%): 25 Hardness (HV1): 220

[0015] As already mentioned above, the container is not limited in shape, size, or design. However, due to its outstanding properties, it is particularly suitable as a hydrogen tank. For the purposes of the present invention, a hydrogen tank is understood to be a container designed for the reversible storage of hydrogen.

[0016] Furthermore, the invention also describes a motor vehicle comprising a container as defined above. Here, the container is also preferably designed as a hydrogen tank and connected to a combustion unit that powers the motor vehicle.

[0017] Furthermore, the invention also discloses a method for producing a container as described above. The method initially comprises a step of providing a container with a cavity for accommodating hydrogen, wherein the inner sides of the container walls facing the cavity are formed from steel. As already explained above for the container according to the invention, the container used in the method is also not limited and can be designed in any shape, size, and form depending on the intended application.

[0018] In a further process step, the inner surfaces of the walls are activated with acid. In other words, the steel is activated by bringing it into contact with an acid or acidic solution, for example, by applying, vaporizing, spraying, or rinsing, so that the inner surfaces of the walls can be galvanized in the next process step.

[0019] Preferably, the steel can be activated with 20% sulfuric acid (vol%). This is brought into contact with the steel for approximately 12 to 15 seconds. This contact can be achieved, in particular, by conducting the sulfuric acid in an activation circuit, using platinized titanium as the cathode and a current density of 2 to 3 A / dm 2 amounts.

[0020] The electroplating that follows activation forms a galvanic metal layer on the steel, so that the cavity of the container includes a hydrogen barrier layer that prevents hydrogen from coming into contact with and penetrating the steel of the walls surrounding the cavity.

[0021] Galvanizing can be performed in the conventional manner. Galvanizing is the electrochemical deposition of metals onto metallic or metallized surfaces using an electrolyte and direct current. While galvanizing is mostly used for surface finishing, the present invention uses it to create an internal surface coating on the steel that improves the hydrogen impermeability of the interior of a container and prevents steel embrittlement. Galvanizing has the advantage over other conventional coating methods that it produces an effective yet uniform coating in a short time, which is important for hydrogen impermeability.

[0022] The process is simple and quick to implement using known technologies and produces a hydrogen-tight container that is mechanically, physically and chemically stable and is ideal for the long-term storage of hydrogen.

[0023] The advantages, advantageous effects and further developments stated for the container according to the invention and the method according to the invention are mutually applicable.

[0024] A particularly uniform galvanic metal layer, and thus a galvanic metal layer with particularly high hydrogen impermeability, can be advantageously formed by pumping an electrolyte of the metal forming the metal layer through the container during the galvanizing process. By pumping the electrolyte through the container, the surfaces to be galvanized are continually surrounded by fresh coating material, i.e., an electrolyte with a constant metal concentration, so that no defects occur in the coating and the galvanic metal layer is formed with a particularly high density.

[0025] To produce a galvanic nickel layer, an electrolyte comprising approximately 60 g / L of nickel sulfate and approximately 40 g / L of boric acid can be used. Furthermore, the electrolyte can comprise a wetting agent. Platinized titanium is used as the anode for this purpose, with a temperature during galvanization being in particular 40 to 60 °C and a pH value of approximately 3.0 to 3.6, and in particular 3.4.

[0026] To prevent foreign body inclusions and thus further increase hydrogen impermeability, the process preferably includes filtering the electrolyte after it has passed through the container and returning the filtered electrolyte to the container. This ensures that the interior surfaces of the container to be electroplated always come into contact with "fresh" electrolyte, creating lattice structures without defects. Filtration can be achieved by passing the electrolyte through another external container equipped with appropriate filters through which the electrolyte passes. The filter used for this purpose has a fineness of 0.001 mm.

[0027] The method also advantageously includes adjusting the concentration of the electrolyte after it has passed through the container and returning the adjusted electrolyte to the container. Adjusting the concentration can, if provided, take place before or after filtration, but preferably after filtration if provided, and can be carried out in particular by an ampere-hour-controlled addition of nickel sulfate from a storage tank via a dosing pump. The constant electrolyte concentration forms a particularly uniform and consistent lattice structure on all inner surfaces of the walls, which further contributes to hydrogen impermeability. Furthermore, the pH value can also be kept constant, which is achieved in particular by a pH-controlled addition of 20% sulfuric acid.

[0028] Particularly advantageous for uniform electroplating, the container comprises two openings, with an anode used for electroplating secured in at least one of the openings. This can be achieved, for example, by screwing the anode into one of the openings. This screwing has the advantage that the anode can be securely attached to the intended location and can also be removed without leaving any residue.

[0029] Furthermore, the invention also discloses a device for carrying out the method described above, with which the container according to the invention can be produced. The device comprises a storage tank for storing an electrolyte solution. The storage tank can also be used to hold an activating acid. From the storage tank, the corresponding medium flows into a working tank via a metering pump. It goes without saying that corresponding components and parts are connected to one another via supply and discharge lines.

[0030] The working tank contains the electrolyte in the appropriate concentration for electroplating (the working tank contains an acid for activation, e.g., 20% sulfuric acid). A mixture of nickel sulfate (60 g / L) and boric acid (40 g / L) is particularly suitable for producing a galvanic nickel layer.

[0031] The device further comprises a container holder for receiving the container to be galvanized (or activated), wherein the container and the working tank are in contact with each other via a dosing pump.

[0032] An anode is inserted into the container in such a way that it is reversibly connected to an inlet closure at one of the container's inlets and an outlet closure at one of the container's outlets. This enables electroplating with minimal technical effort but high quality.

[0033] To promote particularly homogeneous galvanization, the container holder is preferably pivotable.

[0034] To avoid the introduction of foreign particles that could disrupt the formation of the galvanic layer and promote the inclusion of foreign particles, at least one of the dosing pumps comprises a microfilter, which can in particular have a fineness of 0.001 mm.

[0035] Also preferred in view of a uniform layer formation, the anode is designed as a titanium round anode.

[0036] Furthermore, the invention also describes the use of a galvanic metal layer for producing a hydrogen barrier layer inside a hydrogen tank made of steel. The galvanic metal layer applied to the inside of walls surrounding a cavity of a container not only improves the hydrogen impermeability of the steel but also effectively counteracts embrittlement of the steel.

[0037] The advantages, advantageous developments and embodiments of the container according to the invention, the method according to the invention, the device according to the invention and the use according to the invention are each mutually applicable.

[0038] Further details, advantages, and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawings. Fig. 1 a container according to an advantageous further development in section and Fig. 2 a schematic representation of a device for galvanizing a container according to a further advantageous development.

[0039] Only the essential elements of the present invention are shown in the figures. All other elements have been omitted for clarity. Furthermore, like reference numerals refer to like elements or components.

[0040] Fig. 1 shows a container 1, which is shown by way of example in the form of a hydrogen tank, which can be provided in a motor vehicle for storing and providing hydrogen as a propellant.

[0041] The container 1 is rectangular, but can also have any other desired shape and is also not limited in size, depending on the intended use. The container 1 comprises a cavity 2 for holding hydrogen. The hydrogen can be reversibly, i.e., temporarily, absorbed into the cavity 2 and released therefrom, for example through the openings 5a and 5b, which allow hydrogen to flow into the container 1 and out of the container 1. The openings 5a and 5b can be closable.

[0042] The inner sides 6 of walls 3 of the container 1 facing the cavity 2 are made of steel. As shown in this embodiment, the walls 3 are made of steel. However, the walls 3 can also be formed from multiple layers, provided that the innermost layer, i.e., the layer facing the cavity 2, is made of steel.

[0043] The inner sides 6 of the walls 3, formed of steel, further comprise a galvanic metal layer 4 which completely covers the steel.

[0044] The galvanic metal layer 4 is formed from a metal which preferably has a face-centered cubic lattice structure and, due to its high compatibility with hydrogen, consists in particular of nickel.

[0045] The galvanic metal layer 4 can be carried out by galvanizing the container, e.g. by pumping an electrolyte comprising the corresponding metal through the cavity 2 of the container 1, wherein the steel is preferably activated by an acid, in particular 20% sulfuric acid (vol%), before galvanizing.

[0046] Through electroplating, the galvanic metal layer 4 is formed with a particularly uniform lattice structure and high density, so that it forms a very good penetration barrier for the hydrogen present in the cavity 2. In addition, the galvanic metal layer 4 applied to the inner sides 6 of the walls 3 counteracts embrittlement of the steel, thereby achieving high physical and chemical stability in addition to high mechanical stability of the container 1.

[0047] Galvanization can be carried out particularly easily if the anode used for this purpose, which provides the direct current, is screwed into at least one of the openings 5a, 5b. This ensures a uniform current supply and thus a uniform and consistent deposition of the metal as a galvanic layer on the steel, so that a galvanic layer with particularly high impermeability to hydrogen can be provided.

[0048] Preferably, a nickel layer of ultrapure nickel containing at least 99.9% nickel by weight is applied to the steel by galvanizing. A mixture of nickel sulfate and boric acid in a volume ratio of 60:40 is used as the electrolyte.

[0049] The nickel layer has a columnar layer structure and a density of 8.8 g / cm 3 , a melting range of 1435 to 1445 °C and a thermal conductivity at 25 °C of 90 W / mK.

[0050] The nickel layer has the following mechanical properties, which are measured according to DIN EN 10002: Young's modulus (GPa): 180 to 200 Elongation at break L0 (%): 25 Hardness (HV1): 220.

[0051] Fig. Figure 2 is a schematic representation of a device 10 for producing a container 1 for containing hydrogen according to a further advantageous development. The device serves for the simplified and improved electroplating of the container 1.

[0052] An electrolyte solution (e.g. nickel sulfate / boric acid / wetting agent) is transferred from a temperature-controlled (50°C) storage tank 11 via a metering pump 12, which may include a microfilter, into a working tank 13, which is kept at approximately 40 to 45°C. The electrolyte solution is fed via metering pump 14 to the container 1, which comprises a hollow space. The hollow space is formed by walls surrounding this hollow space. The inner sides of the walls facing the hollow space are made of steel. A titanium round anode 15 is inserted into the hollow space and is held inside the container 1 by means of an inlet closure 17a and an outlet closure 17b, whereby a flow of electrolyte through the container 1 is ensured. Reference numeral 18 denotes a container holder which is pivotable so that the electrolyte solution fed into the cavity to the titanium round anode 15 comes into contact with all areas of the steel walls by pivoting the container 1.

[0053] The electrolyte solution is pumped through the cavity of container 1 and then returned to the working tank. By adding electrolyte solution from the storage tank 11, the electrolyte concentration can be kept constant.

[0054] Dosing pump 14, like dosing pump 12, may comprise a microfilter 16 with a fineness of 0.001 mm, so that the electrolyte solution is cleaned of foreign particles before being passed through the container 1, which would hinder a uniform and homogeneous formation of the galvanic layer.

[0055] By connecting the titanium round anode 15 to the inlet closure 17a and the outlet closure 17b, complicated anode arrangements inside the container 1 are eliminated. The device 10 is characterized by a simple structure and functional arrangement of its components, allowing for uncomplicated and high-quality electroplating. The container obtained with the device 10 is ideally suited for absorbing hydrogen, as the electroplated layer is characterized by high hydrogen impermeability and a low embrittlement rate due to the formation of a pure metallic layer.

[0056] The device 10 described above can also be used to activate the steel, with the working tank 13 and the storage tank 11 then filled with acid (e.g., 20% sulfuric acid). Alternatively, the activation can also be carried out in a separate circuit.

[0057] It goes without saying that the individual components of device 10 are connected to each other, where necessary, via appropriate supply and discharge lines. In particular, these supply and discharge lines are chemical-resistant plastic wire hoses.

[0058] In addition to the above written description of the invention, reference is hereby explicitly made to the graphic representation of the invention in the figures for its supplementary disclosure. List of reference symbols 1 container 2 cavity 3 wall 4 galvanic metal layer 5a Opening 5b Opening 6 Inside of the wall 10 Device 11 Storage tank 12 Dosing pump 13 Working tank 14 Dosing pump 15 titanium round anode 16 microfilters 17a Inlet closure 17b Outlet closure 18 Container holder

Claims

[1] Container (1) comprising a cavity (2) for receiving hydrogen, wherein inner sides (6) of walls (3) of the container (1) facing the cavity (2) are formed from steel, and the inner sides (6) of the walls (3) on the steel comprise a galvanic metal layer (4). [2] Container (1) according to claim 1, wherein the metal has a face-centered cubic lattice structure. [3] Container (1) according to claim 1 or 2, wherein the metal is nickel. [4] Container (1) according to one of the preceding claims, designed as a hydrogen tank. [5] Motor vehicle comprising a container (1) according to one of claims 1 to 4. [6] A method for producing the container (1) according to any one of claims 1 to 4, comprising the steps: - Providing a container comprising a cavity (2) for receiving hydrogen, wherein inner sides (6) of walls (3) of the container facing the cavity are formed from steel, - Activating the insides (6) of the walls (3) with acid and - Galvanizing the inner sides (6) of the walls (3) to form a galvanic metal layer (4) on the steel. [7] Method according to claim 6, wherein for electroplating an electrolyte of the metal forming the galvanic metal layer (4) is pumped through the container (1). [8] The method of claim 7, further comprising filtering the electrolyte after passing through the container (1) and returning the filtered electrolyte to the container (1). [9] The method according to claim 7 or 8, further comprising adjusting the concentration of the electrolyte after passing through the container (1) and returning the adjusted electrolyte to the container (1). [10] Method according to one of claims 6 to 9, wherein the container (1) comprises two openings (5a, 5b) and an anode used for electroplating is fixed in at least one of the openings (5a, 5b). [11] Device (10) for carrying out the method according to one of claims 6 to 10, comprising: - a storage tank (11) and a working tank (13) which are in contact with each other via a dosing pump (12), - a container receptacle (18) for receiving the container (1), wherein the container (1) and the working tank (13) are in contact with one another via a metering pump (14), wherein an anode (15) is introduced into the container (1) in such a way that it is reversibly connected to an inlet closure (17a) at an inlet of the container (1) and to an outlet closure (17b) at an outlet of the container (1). [12] Device (10) according to claim 11, wherein the container receptacle (18) is pivotable. [13] Device (10) according to claim 11 or 12, wherein the metering pump (12) and / or the metering pump (14) comprises a microfilter (16). [14] Device (10) according to one of claims 11 to 13, wherein the anode (15) is designed as a round titanium anode. [15] Use of a galvanic metal layer (4) for producing a hydrogen barrier layer inside a hydrogen tank made of steel.

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