Patent Description:
The hydrogen receptacle may be a tank for storing hydrogen, especially liquid hydrogen or a hydrogen pipe for conducting hydrogen, especially liquid hydrogen. Preferred embodiments of the invention relate to a manufacturing method for manufacturing a hydrogen tank wall, especially a cryogenic tank wall. Further, preferred embodiments of the methods according to the invention relate to manufacturing a hydrogen tank, especially a cryogenic tank, for a vehicle, especially an aircraft, comprising a tank wall component having a substrate of fibre reinforced composite material. The principles of preferred embodiments also apply to other lightweight hydrogen receptacles used on an aircraft, especially pipes.

For technical background, reference is made to the following citations:.

Cryogenic storage tanks may be used for storing liquid hydrogen, for example, for use as a fuel for driving a vehicle. The vehicle may be a motor vehicle such as a car, lorry or train or may be an aircraft. Citations [<NUM>] and [<NUM>] disclose a tank for the cryogenic storage of hydrogen and an aircraft with a tank installed therein. Liquid hydrogen stored within the tank is used as a fuel for the aircraft engine in place of carbon-based fuels such as kerosene. The cryogenic storage tank is typically substantially cylindrical and includes openings for allowing the tank to be filled with hydrogen as well as to supply the stored liquid hydrogen to the engine. Further, the aircraft is equipped with a hydrogen duct system including hydrogen pipes for conducting hydrogen through the aircrafts.

Lightweight energy storage is a key topic for next generation aircrafts. Storage systems with high energy density are one of the key challenges for future electrical propulsion-based systems. Different energy storage systems are available today, whereas pressurized (~<NUM> bar) or cryogenic Hydrogen (<NUM> < T < <NUM>) paired with fuel cells or direct burn are interesting solutions for next flight vehicles. Hydrogen (H2) is the molecule with lowest density and smallest diameter in nature, which is why the storage in tanks is very complex and hardly achievable without leakage over longer durations.

Hydrogen offers high energy densities, whereas the storage technique (cryogenic, compressed, solid state/absorbed) is a key issue. Hydrogen can be compressed and/or cooled down to cryogenic temperatures to increase the volumetric and gravimetric energy density. Usually, complex tank systems are needed with individual requirements to the materials, design and working principle e.g., regarding operational safety.

Compressed and cryogenic hydrogen are the techniques of choice for today's vehicles, like cars or airplanes. Cryogenic tanks can achieve the lowest added weight wherein, with the present known technologies, about <NUM> - <NUM> tank weight is needed per kg stored H2. Conventional tanks work with applied inner pressure to avoid gas ingress from outside. As tank material typically metals, metal alloys and composites are in use. Full composite tanks can be challenging because of the long in-service life of civil aircraft. Hydrogen leakage may also be an issue.

An object of the invention is to improve the manufacturing of hydrogen receptacles, especially tanks or pipes, made of composite material for storing or conducting hydrogen such that they can be filled more quickly or can conduct hydrogen with a higher velocity.

The object is achieved by the subject-matter of the independent claims.

Preferred embodiments are subject-matters of the dependent claims.

Preferred embodiments of the invention provides an enhanced manufacturing of a hydrogen receptacle for a vehicle, especially an aircraft, comprising a receptacle wall made from fibre reinforced composite material defining a volume for storing or conducting hydrogen, especially liquid hydrogen, wherein the receptacle wall comprises an inner layer of graphene.

Preferably, the inner layer of graphene is a coating, especially a liner, of an inner surface of the receptacle wall.

Preferably, the inner layer of graphene is a coating of the complete inner surface of the receptacle wall.

Preferably, the inner layer of graphene is a layer electrically connected to a ground or mass potential.

Preferably, the inner layer of graphene is a cover over voids in the fibre reinforced composite material.

Preferably, the inner layer of graphene is a layer configured to suppress permeation of hydrogen through the receptacle wall.

Preferably, the receptacle wall is made from CFRP.

Preferably, the receptacle wall comprises a CFRP laminate having a combination of at least two of the layers selected from the group of a resin rich layer made from polymer matrix, a CFRP ply with fibres in a first direction, and a CFRP ply with fibres in a second direction.

Preferably, the receptacle wall comprises a CFRP laminate having at least one CFRP ply with unidirectional fibres sandwiched between resin rich layers made from polymer matrix.

In some embodiments, the hydrogen receptacle achieved by the manufacturing method is a hydrogen tank for storing hydrogen wherein the receptacle wall is a tank wall. In some embodiments, the hydrogen receptacle is a hydrogen pipe for conducting hydrogen wherein the receptacle wall is a pipe wall.

The invention provides a manufacturing method for manufacturing a hydrogen receptacle wall component, comprising the steps of:.

Preferably, step a) comprises:
providing a carbon fibre reinforced plastic composite tape.

Preferably, step a) comprises:
providing a laminate from fibre reinforced composite material, especially CFRP.

According to the invention, step a) comprises:
a3) providing a tape made from fibre reinforced composite material.

According to the invention, step b) is conducted before step c).

Preferably, step b) comprises:
covering voids of the fibre reinforced composite material with the graphene layer.

Preferably, step b) comprises:
coating an inner surface of the wall material which in use forms an inner receptacle wall surface with the graphene layer.

Preferably, step b) comprises:
spraying of multiple graphene flakes.

According to the invention, step b) comprises:
covering one side of the tape from fibre reinforced composite material with graphene.

Preferably, step b) comprises:
applying graphene layer on an CFRP tape.

According to the invention, step c) comprises:
applying the wall material to a forming tool.

Preferably, step c) comprises:
winding the wall material in form of the tap on a mandrel.

Preferably, step c) comprises:
pressing the wall material against the forming tool with a compaction tool, especially a compaction roller.

Preferably, step c) comprises:
forming the wall material to a cylindrical wall.

According to the invention, step c) comprises:
applying several layers of wall material onto the forming tool, especially the mandrel, wherein a first layer coated with graphene is applied with the graphene coated side contacting the forming tool.

Preferably, step c) comprises:
wind an inner layer of CFRP LH2 tank with a tape, especially a CFRP tape, with graphene layer applied and then wind remaining CFRP plies on a mandrel.

Preferably, step c) comprises:
curing the wall material after forming.

Preferably, wall components for hydrogen tanks or hydrogen pipes are manufactured with a wall material of fibre reinforced composite material, especially CFRP, and an inner layer of graphene.

According to another aspect, the invention provides a hydrogen receptacle manufacturing method for manufacturing a hydrogen receptacle for a vehicle, especially an aircraft, wherein the hydrogen receptacle comprises a receptacle wall made from fibre reinforced composite material defining a volume for storing or conducting hydrogen, especially liquid hydrogen, the hydrogen receptacle manufacturing method comprising the steps of:.

Preferably, one or several cylindrical receptacle components with an inner graphene layer are provided. The cylindrical receptacle components may be tank components or pipe components.

Preferably, step d) comprises assembling at least one cylindrical wall component made from fibre reinforced composite material with an inner graphene layer and a first and a second dome shaped end component, especially from metal, in order to achieve the hydrogen tank.

In a preferred embodiment, the hydrogen receptacle manufacturing method comprises:
g) testing the hydrogen receptacle under pressure.

In a preferred embodiment, the hydrogen receptacle manufacturing method comprises:
h) test the hydrogen receptacle for permeation.

Preferably, the method according to any of the aforementioned embodiments comprises:
e) verifying electrical ground function of the graphene layer.

Preferably, the method according to any of the aforementioned embodiments comprises:
f) verifying permeation suppression of the graphene layer.

According to another aspect, the invention provides an aircraft comprising at least one hydrogen consumer and at least one hydrogen receptacle, especially hydrogen tank and/or hydrogen pipe, achievable by the hydrogen receptacle manufacturing method according to any of the aforementioned embodiments or comprising at least one hydrogen receptacle wall component achievable by the wall component manufacturing method according to any of the aforementioned embodiments.

Preferred embodiments of the invention relate to manufacturing of CFRP LH2 tank with inside surface layer of multi-functional graphene. Similar principles also apply to other components of a LH2 system containing LH2 such as pipes made from CFRP.

The graphene layer may function against static electricity and permeation. Preferred embodiments of the hydrogen tank achievable by the method have the advantage that they can be filled more quickly. Preferred embodiments of the hydrogen pipe achievable by the method have the advantage that they can conduct hydrogen with a higher velocity.

Preferred embodiments of the hydrogen receptacles such as tanks and pipes have the advantage that they have less H2 permeation.

The graphene layer may provide a smooth surface without voids.

In preferred embodiments, the graphene layer may improve the possibility to clean the inner side of the receptacle such as the tank or the pipe.

In preferred embodiments, the graphene layer may enable or improve a laminar flow inside the receptacle especially along the inner receptacle wall side. Preferred embodiments of the hydrogen receptacle have the advantage of less accumulation of foreign matter on the inner receptacle wall.

Filling of LH2 needs to be speedy. At fast fillings in receptacles or containers not made of a conducting material, e.g., metal, static electricity build-up can occur. Furthermore, the issue of hydrogen permeation exists for pure CFRP tanks or pure CFRP pipes.

Graphene is a good electrical conductor, and has shown promising results together with CFRP for e.g., leading away energy at lightning strike. In preferred embodiments, this feature of graphene is used to suppress static electricity build-up. At the same time, graphene is a dense material on a microscopic scale, used e.g., as tightening layer against liquids, and may be helpful for suppressing permeation.

In preferred embodiments, graphene is used as multi-functional material.

Preferred embodiments of the invention have advantages with relation to low or even zero emission vehicles, especially aircrafts, for a better liquid hydrogen storage, in order to improve CFRP tanks or CFRP pipes, avoiding or reducing static electricity, and/or avoiding or reducing permeation.

Preferred embodiments of the invention have advantages in relation to liquid hydrogen tanks, CFRP pressure vessels, reducing porosity in CFRP, reducing accretion build-up, particle build-up, trapped bubbles, and/or enhancing laminar/turbulent flow.

Some embodiments of the invention relate to manufacturing of a multi-functional graphene layer for LH2 tank for improved maintenance and permeation characteristics.

Until now, all pressure vessels used over long term with liquid content needed inspection and maintenance procedures. Included were cleaning of accretion, chemical build-up. This is greatly simplified and improved by internal surface characteristics displaying no or minimal pores. The strive towards CFRP for LH2 tanks will require solutions for this. A material that is well compatible with CFRP, which displays no pores and offers high suppression of permeation is graphene. This can be applied e.g., by spraying.

Embodiments of the invention are explained below referring to the accompanying drawings in which:.

In the following, a hydrogen receptacle <NUM> for a vehicle <NUM>, especially an aircraft, and manufacturing methods therefore are explained with reference to the accompanying drawings. The hydrogen receptacle <NUM> is configured to contain hydrogen, especially liquid hydrogen (referred to as LH2 in the following). Especially, the hydrogen receptacle <NUM> is configured to store or to conduct LH2. The hydrogen receptacle comprises a receptacle wall <NUM> made from fibre reinforced composite material defining a volume <NUM> for storing or conducting hydrogen, especially LH2. The receptacle wall <NUM> comprises an inner layer <NUM> of graphene. Examples for the hydrogen receptacle <NUM> are hydrogen tanks <NUM> and hydrogen pipes <NUM>. The principles of the preferred embodiments will be described mainly with relation to tanks, but they are also applicable to pipes or other hydrogen receptacles <NUM>.

<FIG> shows an aircraft, especially an airplane <NUM> as an example for a vehicle <NUM> in which a hydrogen tank <NUM> is used. The airplane <NUM> has a propulsion system <NUM> with turbines <NUM> as engines <NUM>. The turbines <NUM> are configured to burn hydrogen supplied from the hydrogen tank <NUM>. Further, the airplane <NUM> may be equipped with fuel cells (not shown), wherein hydrogen is supplied to the fuel cells from the hydrogen tank <NUM>.

The hydrogen tank <NUM> has, e.g., a cylindrical shape. The hydrogen tank <NUM> is configured as a cryogenic tank for storing LH2 at cryogenic temperatures. At least one wall component <NUM> of the tank, such as for example the middle cylindrical part <NUM> is made of fibre reinforced composite material, especially CFRP (=carbon fibre reinforced plastic). The hydrogen tank <NUM> further comprises end caps <NUM> which may also be made from fibre reinforced composite such as CFRP (so that they are further examples for the fibre reinforced composite wall component <NUM>) or are - as presently preferred - made from metal. The inner surface <NUM> of the wall component <NUM> is coated with a coating <NUM> of graphene. Here, the inner surface <NUM> is the surface having contact with the LH2.

<FIG> shows a schematic block diagram of an exemplary manufacturing apparatus <NUM> for manufacturing the hydrogen tank <NUM>. The manufacturing apparatus <NUM> comprises a wall component manufacturing unit <NUM>, a graphene applying unit <NUM> and a tank assembly unit <NUM>. The wall component manufacturing unit <NUM> is configured for manufacturing the wall component <NUM> made from fibre reinforced composite material. The graphene applying unit <NUM> is configured to apply a layer <NUM> or liner of graphene onto at least one surface, especially the inner surface <NUM>, of the wall component <NUM>. The applying of graphene may be made by any suitable graphene production technique as known, for example, from [<NUM>] or [<NUM>]. Preferably, the graphene applying unit <NUM> is configured to apply the graphene by spraying multiple graphene flakes onto the surface. The tank assembly unit <NUM> is configured to assemble the at least one wall component <NUM> coated by graphene together with further components to form the hydrogen tank <NUM>.

<FIG> shows a schematic perspective view of an example for the wall component manufacturing unit <NUM>. The wall component manufacturing unit <NUM> comprises a winder <NUM> onto which several layers of CFRP laminates <NUM> can be wound in order to achieve the wall component <NUM>.

<FIG> shows a schematic view of a comparative example of the graphene applying unit <NUM> together with the wall component <NUM> to be coated with graphene. The wall component <NUM> is manufactured and provided as an essentially cylindrical wall element with openings <NUM>. The graphene applying unit <NUM> comprises a robotic arm <NUM> adapted and configured to pass through the opening <NUM> and equipped with a graphene spray head <NUM> as shown in <FIG>. The graphene applying unit <NUM> is configured to coat the inner surface of at least one wall component <NUM> of the hydrogen tank <NUM> with graphene.

As mentioned above, there are different ways to apply a graphene layer at the receptacle inner surface <NUM>, such as the inner surface of the hydrogen tank <NUM>. There are different ways to apply a graphene layer at the tank inner surface. One way is by spraying a solution containing graphene "flakes", shown in <FIG>.

<FIG> shows an example of the graphene spray head <NUM>. Especially, <FIG> shows the application of the graphene layer <NUM> on the surface <NUM> by spraying graphene flakes <NUM>. The detail of <FIG> show an enlarged view of such a graphene flake <NUM>. A graphene flake <NUM> is <NUM> to <NUM> long and has a thickness of about <NUM> to <NUM> carbon atoms. The graphene spray head <NUM> comprises a container <NUM> with solvent containing graphene flakes <NUM> and a spray gun <NUM>. The <FIG> display a detail of one graphene "flake" <NUM>, which is <NUM> to <NUM> long and consists of one layer of carbon-atoms. The solvent is kept in the container <NUM> which is connected to the spray gun <NUM>, by which the solvent is sprayed onto the surface <NUM>.

It is clear from <FIG>, that the manufacturing method as described before also works for manufacturing the hydrogen pipe <NUM>.

In the following, several advantages and effects of the hydrogen receptacle <NUM> with inner graphene liner will be described referring to <FIG>, <FIG>. Therein, <FIG> and <FIG>show different situations wherein hydrogen receptacles <NUM> with receptacle walls <NUM> made of CFRP which are still not provided with a graphene layer are used while the <FIG>, <FIG>, <FIG> show the same situations wherein the inner surface <NUM> of the receptacle walls <NUM> made from the same wall materials <NUM> is provided with the graphene layer <NUM> in accordance with embodiments of the invention.

Referring now to <FIG>, lightweight hydrogen receptacles <NUM> the walls <NUM> of which are not coated are shown during filling with a liquid <NUM> from a liquid container <NUM>. Further, <FIG> shows enlarged details of an area near a wall of the hydrogen pipe <NUM> and of an area near the bottom wall of the hydrogen tank <NUM> shown in an uncoated state in order to explain the effect of static electricity in liquid containers.

It is well established that when a gas or liquid passes over a surface at a sufficient velocity, static electricity may be built up by charged particles <NUM>, <NUM>, on the one hand in the gas/liquid, and on the other hand at the surface <NUM>. A well-known example in aeronautics is static electricity on the wing covers.

The phenomenon appears typically when the surface <NUM> is not made of an electrically conducting material, i.e., the charged particles cannot be led away. Static electricity may be built up when a liquid is flushed at a high velocity over a surface <NUM>, such as is the case when filling a tank <NUM>. In <FIG> liquid <NUM> from a container <NUM> is filled through a pipe <NUM> into a tank <NUM> at a high velocity. Tank <NUM> and pipe <NUM> is made of a non-conducting material. Static electricity is built up in pipe <NUM> and in tank <NUM>.

<FIG> shows a lightweight hydrogen tank <NUM> with a still uncoated tank wall <NUM> partly filled with LH2 <NUM> together with an enlarged view of a detail thereof near an upper wall portion. <FIG> shows a LH2 tank <NUM>. The illustration on the left shows a cross-section of a cylindrical tank with hydrogen in both liquid <NUM> and gas form <NUM>. The illustration on the right shows a detail with gas permeation <NUM> through material of the tank wall <NUM>. In this instance the tank wall <NUM> is built of CFRP, and will therefore display particular permeation, if no separate measures are taken to suppress it.

<FIG> shows the situation as in <FIG> wherein the tank wall <NUM> is provided with the graphene layer <NUM> in accordance with embodiments of the invention. <FIG> shows a lower part of the tank wall provided with the graphene layer <NUM> which is electrically connected to ground <NUM>.

An embodiment of the CFRP LH2 tank <NUM> as shown in <FIG> and <FIG> includes a multi-functional inner layer <NUM> of graphene for suppression of static electricity build-up as well as suppression of permeation. The graphene layer <NUM> is electrically grounded (i.e., electrically connected to earth).

<FIG> shows the inner graphene layer <NUM> in the CFRP LH2 tank <NUM>, wherein a section of the tank <NUM> is shown in the left illustration, and a detail depicted on the right side of <FIG> shows how charged particles of the material surface are led to earth, thus the charged particles in the liquid get dispersed. Especially, <FIG> shows a liquid hydrogen tank <NUM> in accordance with an embodiment of the invention. To the left a partial cross-section through the tank <NUM> is seen, with liquid hydrogen and gaseous hydrogen. The tank <NUM> has the inner surface layer <NUM> of graphene (a graphene "liner"). To the right a detail is seen of a section with liquid hydrogen <NUM>. It is seen that the charged surface particles <NUM> are led away in the graphene layer <NUM>, which is connect to ground (earth) <NUM>. Once they are led away the oppositely charged particles <NUM> in the liquid get dispersed, and so no build-up of a charge can take place any longer.

<FIG> illustrates the permeation suppression in the CFRP LH2 tank <NUM> by the graphene layer <NUM>. In more detail, <FIG> shows the same liquid hydrogen tank <NUM> as in <FIG>, i.e., a CFRP tank <NUM> with a graphene inner layer (liner) <NUM> however here focussing on permeation. To the left, a partial section is shown with an overpressure of hydrogen gas <NUM>. To the right a detail shows that gas that would permeate without the graphene layer <NUM>, here is hindered from penetrating the graphene layer <NUM>.

Hence, there are several advantages in applying a graphene layer <NUM> to wall components <NUM> of hydrogen receptacles <NUM> some of them are listed in the following:.

For applying the graphene layer <NUM>, embodiments of the manufacturing method make use of graphene flakes <NUM> ready in solvent and a spray gun <NUM>. An embodiment of the manufacturing method comprises the steps of.

However, applying a graphene layer to fibre reinforced composite material of or for a wall component <NUM> of a hydrogen receptacle provides even more advantages as listed above. Those further effects and advantages are explained in more detail in the following.

<FIG> shows a sectional view through a wall material <NUM> for the wall component <NUM> of the hydrogen receptacle <NUM> made of CFRP being still uncoated in order to illustrate potential issues of a porosity of the CFRP material.

<FIG> shows a typical cross-section of a carbon fibre reinforced plastic (CFRP). Especially, a ply <NUM> is shown as an example for the wall material <NUM>. The ply <NUM> has a polymer matrix and carbon fibres <NUM> embedded therein. The ply <NUM> has resin rich layers <NUM>. On the surface thereof, there areas of a pore free surface and areas with open pores <NUM> in the surface. The total thickness <NUM> of the ply <NUM> varies typically between <NUM> (ultra-thin) and <NUM> (thick). Typical standard thicknesses are, <NUM> (thin), <NUM> (medium), and <NUM> (thick). Thicknesses below <NUM> are defined as "thin plies".

In the resin various pores are usually present, defined by a porosity content. This is dependent on the curing process, and includes parameters such as pressure and temperature during curing. The pores may vary in size from <NUM> up to appr. The pores are present within the resin, and may appear in the surface as open pores <NUM>, such as seen in <FIG> shows a cross-section of a typical CFRP ply <NUM> with pores shown internally as well as crossing the surface.

<FIG> shows a cross-section of a cylindrically shaped liquid hydrogen tank <NUM> built of a laminated CFRP shell on the left side. The situation is shown where the tank wall <NUM> is manufactured with a CFRP laminate <NUM> of several plies <NUM> as shown in <FIG> without surface treatment. The tank <NUM> is partially filled with liquid hydrogen <NUM> and to a part with gaseous hydrogen <NUM>. An over pressure of Δp bar exists in the tank <NUM>. Permeation of hydrogen <NUM> takes place through the CFRP laminate <NUM>.

To the right a detail of the CFRP laminate <NUM> is shown, here for simplicity with only three plies <NUM>, 94T, <NUM>, two transverse 94T and one longitudinal <NUM>. On the inside of the shell, a surface <NUM> with some open pores <NUM> is visible.

<FIG> illustrates the fluid dynamics with a porous surface as it would happen when using the CFRP laminate <NUM> without surface treatment of the inner ply <NUM> thereof. <FIG> illustrates a liquid flow over a smooth surface (left) displaying laminar flow <NUM>, and over a void (right) displaying turbulent flow <NUM> near the void.

Given a liquid hydrogen tank <NUM> built of CFRP and no particular liner installed on the inside of the CFRP pressure vessel, we obtain the case of a fluid acting on a porous surface. We will here summarize the physics of this case in the particular case of a pressure vessel, to be filled with a liquid medium which will be repeatedly filled and evacuated.

<FIG> shows a liquid flowing nearby a solid surface that is smooth (left). The liquid velocity <NUM> is shown by means of a velocity diagram as function of the distance to the surface. Right at the surface <NUM> the velocity of the liquid is zero, and it increase by a parabolic function of the distance. The flow in the liquid is here laminar at all distances.

To the right a surface <NUM> with a void is shown, here made up by an open pore <NUM> in the CFRP resin at the surface <NUM>. It can here be seen that a turbulent flow is taking place near the surface, and the distribution <NUM> of the flow velocity is also changed.

For liquid pressure vessels in operation over years with multiple evacuations and refilling experience has shown that tiny particles <NUM> may build up on the inside of the pressure vessel. In particular this has proven to be the case at voids in surfaces. <FIG> shows the case of an open pore <NUM> with tiny particle build-up <NUM>. The particles <NUM>, <NUM> can be foreign materials transported with the liquid medium, or can be the result of chemical reactions. The particle build-up <NUM> can contribute to further turbulent flow.

For maintaining proper function over longer time, it is advantageous to be able to either clean the inner tank surface <NUM> from undesired particle build-up <NUM>, (which is often performed by flushing the tank <NUM>); since pressure vessels are often designed so as not to be disassembled, the best option is to utilize such an inner surface <NUM> that permits as little particle build-up <NUM> as possible. Clean surfaces are essential to rapid filling and evacuation under laminar flow.

Experience has also proven that tiny bubbles <NUM>, <NUM> will develop, in particular at high liquid velocities, and at obstacles. In voids, bubbles <NUM> may be arrested and may gather in such a manner that they remain, see <FIG>. In such cases, bubble build-up <NUM> can contribute to further turbulent flow. <FIG> shows bubbles <NUM> trapped in open voids inside the tank <NUM>, contributing to turbulent flow.

Also here applies that an inner tank surface <NUM> that does not permit bubbles <NUM> to be trapped and bubble-build-up <NUM> is a preferred option.

Such advantageous smooth surfaces <NUM> can be achieved by the graphene coating <NUM>.

A 2D layer of one atom thickness of carbon is defined as "graphene". Within the last <NUM> years, graphene has been intensively researched, and found to possess numerous interesting characteristics.

The manufacturing of graphene layers <NUM> involve chemical exfoliation from graphite, and is described in the literature. Graphene can be provided e.g., in limited "flakes", see <FIG>.

For practical applications, graphene can be applied on a material surface <NUM> as a layer <NUM>. Such a graphene layer <NUM> may consist of a multitude of graphene flakes <NUM> that are e.g., sprayed on to the surface, see <FIG> or <FIG> which illustrates the step of applying graphene according to another embodiment of the manufacturing method.

<FIG> shows an embodiment capable of performing the method according to the invention of the graphene applying unit <NUM> wherein graphene is applied on the wall material <NUM> before the wall component <NUM> is formed from the wall material <NUM>. As described before referring to <FIG>, the graphene applying unit <NUM> comprises the robotic arm <NUM> and the graphene spray head <NUM> with the container <NUM> with solvent as graphene flake source and the spray gun <NUM> with a spraying nozzle. <FIG> further shows the CFRP laminate <NUM> in form of a tape, a material spool <NUM> containing rolled CFRP tape with graphene coating <NUM>.

In other instances, different processes can be used for applying graphene onto a substrate, such as e.g., additive manufacturing with dispersed graphene particles, or using graphene bucky paper.

A CFRP tape coated with graphene has proven to possess several beneficial characteristics, such as smooth surface texture, mechanical, thermal and electrical properties.

With manufacturing methods according to embodiments of the invention, one can achieve an inside coating <NUM> of a CFRP LH2 tank <NUM>, that is sufficiently free of voids so as enable a long term maintenance of the inner tank surface <NUM>, virtually free of: voids causing turbulent flow, particle build-up and bubble build-up, that both can cause added turbulent flow, by applying an inner layer <NUM> of graphene, e.g. by spraying of graphene flakes <NUM> in a multitude of atom-layers, multi-functionally also suppressing hydrogen permeation, the graphene layer <NUM> still being very thin compared to any metal layer, and displaying good material compatibility with the CFRP as a substrate. Advantageously, a clean tank inner surface <NUM> is achieved, with easy maintenance, enabling rapid filling and evacuation, taking place under laminar flow near the surface.

<FIG> shows a CFRP laminate <NUM> in form of a tape being laid down on a mandrel <NUM> (example for forming tool) within the first steps of a manufacturing process of building a CFRP cylindrical LH2 tank <NUM>. For simplicity it is here assumed that the cylindrical region is made by CFRP and the conical end domes of metal. The principles discussed here apply as well to complete CFRP LH2 tanks.

In <FIG> it is seen that the innermost ply <NUM> is laid down in a winding process involving a tape laying head <NUM>, the material spool <NUM> and a robotic arm <NUM>. The mandrel <NUM> rotates and provides the shape of the tank <NUM>. The tape used for the innermost ply is a CFRP tape coated with a graphene layer <NUM>, as shown in <FIG>, in this instance by spraying a multitude of graphene flakes <NUM> onto the tape, providing an even and virtually void free coating. The tape laying head <NUM> holds the material spool <NUM> and comprises a compaction roller <NUM> configured to press the tape onto the mandrel <NUM>.

<FIG> shows a detail of the innermost CFRP ply <NUM>, used as the inner surface <NUM> in the LH2 tank <NUM>. In the picture a void <NUM> is seen. The surface <NUM> is covered by a coating <NUM> of graphene, e.g., applied by the spraying procedure shown in <FIG>. For larger voids the carbon flakes <NUM> in the first flake layer will fall through, but layer by layer, the void is getting covered. It should be noted that the number of flake layers seen here are simplified, and will in reality be considerably larger.

<FIG> shows a cross-section of the resulting CFRP LH2 tank <NUM> (left), with a coating <NUM> of graphene on the innermost ply <NUM>, 94T. The detail of the CFRP laminate <NUM> (right) displays the graphene coating <NUM>, in this instance applied by spraying graphene flakes <NUM>. In the detail it is seen that the smooth surface of the graphene coating <NUM> results in laminar liquid flow <NUM>, and that any particles <NUM> in the liquid are not causing build-up, and there is no bubble build-up. In the cross-section is seen that the hydrogen permeation is reduced by the graphene layer <NUM> (left). <FIG> shows a cross-section of the CFRP LH2 tank <NUM> with graphene coating <NUM> on the inside (left) and detail of CFRP laminate <NUM> including the graphene coating <NUM> (right) displaying full laminar flow <NUM>, no particle build-up and no bubble build-up, and the reduced hydrogen permeation is indicated (left).

Hence, some advantages of applying graphene coating <NUM> to a wall material <NUM> of a hydrogenic receptacle <NUM> are:.

Embodiments of the methods for manufacturing and operation comprise the following steps:.

Claim 1:
Manufacturing method for manufacturing a hydrogen receptacle wall component (<NUM>), comprising the steps of:
a) providing a wall material (<NUM>) made from fibre reinforced composite material,
b) coating the wall material (<NUM>) with a graphene layer (<NUM>), and
c) forming the hydrogen receptacle wall component (<NUM>) from the wall material (<NUM>), characterized in that step b) is conducted before step c), ,
wherein step a) comprises:
a1) providing a tape made from fibre reinforced composite material, in that step b) comprises.
b1) covering one side of the tape from fibre reinforced composite material with graphene, and
in that step c) comprises
c1) applying several layers of wall material (<NUM>) onto a forming tool, especially a mandrel (<NUM>), wherein a first layer in form of the tape coated with graphene is applied with the graphene coated side contacting the forming tool.