WO2024132150A1

WO2024132150A1 - Polymer-graphene composite material and hydrogen carrier for hydrogen storage and/or transport

Info

Publication number: WO2024132150A1
Application number: PCT/EP2022/087476
Authority: WO
Inventors: Mamoun TAHER; Guillaume RATOUIT
Original assignee: Graphmatech Ab
Priority date: 2022-12-22
Filing date: 2022-12-22
Publication date: 2024-06-27

Abstract

The present patent disclosure relates to a polymer-based composite material comprising a polyethylene- based polymer matrix and reduced graphene oxide in an amount of 0.1%-15% in weight per weight of the polyethylene-based polymer matrix. Also disclosed are hydrogen carriers for hydrogen storage and/or transport, the hydrogen carrier comprising a hollow body comprising the polymer-based based composite material.

Description

POLYMER-GRAPHENE COMPOSITE MATERIAL AND HYDROGEN CARRIER FOR HYDROGEN STORAGE AND/OR TRANSPORT

The present patent disclosure is within in the field of hydrogen transport and storage and polymer-based materials for such transport and storage. Particular embodiments concern a polymer-based composite material, an assembly for hydrogen storage and/or transport, a method for manufacturing such assemblies and use of the polymer-based composite material.

In recent years there has been an increased interest in the use of hydrogen as in fuel cells to create electrical energy. Provided that the green hydrogen is created in a process that does not produce carbon dioxide it can be regarded as a zero-carbon electricity source.

For hydrogen to reach its full potential as a clean energy source, however, the hydrogen will need to be transported to where it is to be used, which could be far away. For example, hydrogen may have to be transported from hydrogen production sites to factories, or inside different vehicles such as cars, trucks and buses where hydrogen can be used as a source of fuel. Due to its small size, it is challenging to transport hydrogen, both in its liquid and gaseous state. It is highly permeating and therefore hard to enclose. Hydrogen carriers, such as hydrogen storage containers and hydrogen transport pipes, can be used to store and/or transport hydrogen, for instance as liquid hydrogen or pressurized gaseous hydrogen gas.

In recent years numerous reports have discussed the problem with increased amounts of hydrogen in the air. It has been discussed that hydrogen in the air affects other substances such as methane, ozone and water vapour. This results in hydrogen to be considered an indirect greenhouse gas with an estimated global warming potential of 5.8 over a 100-year time horizon. Therefore, hydrogen leakage into the atmosphere is unwanted and is a potential risk for the hydrogen economy.

US 2022/0003362 according to its abstract states that a plant for delivering hydrogen includes a hydrogen tank and at least one pipe for delivering hydrogen. At least one surface of the hydrogen tank or the hydrogen delivery pipe is covered with a two-dimensional material mixed with a polydopamine- type polymer.

It is an object, among objects, to provide improved hydrogen carriers for hydrogen storage and/or transport. It is also an object, among objects, to provide improved materials that can be used in hydrogen carriers for hydrogen storage and/or transport. To this end, there is provided a polymer-based composite material comprising a polyethylene-based polymer matrix and reduced graphene oxide in an amount of 0.1%-15% in weight per weight of the polyethylene-based polymer matrix.

The provided polymer-based composite material comprising reduced graphene oxide shows a reduced hydrogen permeability compared to bare polyethylene-based polymer, such as HDPE. The obtained experimental results for composite materials falling within this scope described below and in Figure 3 show a clear trend of decreasing hydrogen permeability the more reduced graphene oxide is in the composite material. At the same time, at the above noted reduced graphene oxide concentration range of 0.1 wt% to 15 wt% relative to the polyethylene-based polymer matrix, the composite material can be processed using standard polymer processing techniques, such as injection moulding, rotational moulding, compression moulding, blow moulding and/or extrusion. At concentrations of reduced graphene oxide above 15 wt%, the composite material becomes relatively cumbersome to process, even though the hydrogen permeability would be lower than for lower concentrations of reduced graphene oxide in the composite material.

The presence of the reduced graphene oxide in the composite material has the additional benefit that the composite material becomes more electrically conductive than the bare polyethylene-based polymer matrix without reduced graphene oxide present. As mixtures of hydrogen with air have a relatively low ignition energy, electrical discharge can be a problem when storing and transporting hydrogen. In applications where the composite material is in contact with hydrogen, the safety is improved, as there is a lowered chance of electrical discharges from static electricity built-up on the polyethylene-based polymer.

In an embodiment, the reduced graphene oxide is distributed and/or dispersed in the polyethylene-based polymer matrix. The reduced graphene oxide is preferably homogeneously distributed and/or dispersed in the polyethylene-based polymer matrix. Advantageously, distributed and/or dispersed reduced graphene oxide is beneficial in terms of gas permeability, such as hydrogen gas permeability.

In an embodiment, the polymer-based composite material comprises the reduced graphene oxide in an amount of 0.5%-9% in weight per weight of the polyethylene-based polymer matrix. This range results in a composite material having an advantageous combination of lowered hydrogen permeability and processability of the composite material using the standard polymer processing techniques.

In an embodiment, the amount of reduced graphene oxide in the polymer-based composite material is 0.5%-5% in weight per weight of the polyethylene-based polymer matrix. This range results in a composite material having an even more advantageous combination of lowered hydrogen permeability and processability of the composite material using the standard polymer processing techniques.

In an embodiment, the amount of reduced graphene oxide in the polymer-based composite material is 2.5%-5% in weight per weight of the polyethylene-based polymer matrix.

In an embodiment, the amount of reduced graphene oxide in the polymer-based composite material is 3%-5% in weight per weight of the polyethylene-based polymer matrix.

In an embodiment, the amount of reduced graphene oxide in the polymer-based composite material is 3.4%-5%, preferably 3.8%-5%, in weight per weight of the polyethylene-based polymer matrix. These concentration ranges of reduced graphene oxide particularly has a combination of reduced hydrogen permeability and reduced electrical resistivity.

In an embodiment, the polymer-based composite material further comprises nanoclay.

In an embodiment, the polymer-based composite material comprises the nanoclay in an amount equal to 90 to 110 wt% per weight of reduced graphene oxide.

In an embodiment, the nanoclay comprises, or consists of, layered mineral silicate-based nanoparticles.

In an embodiment, the layered mineral silicate-based nanoparticles comprise one or more selected from the group consisting of montmorillonite nanoparticles, bentonite nanoparticles, kaolinite nanoparticles, hectorite nanoparticles, halloysite nanoparticles.

In an embodiment, the reduced graphene oxide in the polymer-based composite material comprises a Li-salt. Results on hydrogen permeability show an even lower hydrogen permeability for the polymer- based composite materials comprising reduced graphene oxide and the Li-salt.

In an embodiment, the polymer-based composite material comprises the Li-salt in a concentration of 1 to 50 wt%, preferably 2 to 30 wt%, more preferably 5 to 20 wt%, per weight of reduced graphene oxide.

In an embodiment, the Li-salt is lithium bis(salicylate)borate. In an embodiment, the polymer-based composite material comprises the lithium bis(salicylate)borate in an amount in the range of 1 to 50 wt%, preferably 2 to 30 wt%, more preferably 5 to 20 wt%, per weight of reduced graphene oxide. The exact amount of added Li-salt, such as the lithium bis(salicylate) borate, is not important. The addition of the Li-salt within the indicated ranges beneficially improves the dispersion and/or interaction of the rGO with the polymer.

In an embodiment, the polymer-based composite material comprises the Li-salt in the range of 1-50 wt% relative to the reduced graphene oxide, preferably 4-20 wt%, more preferably 6-15 wt%, for instance 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, or 14 wt% relative to the reduced graphene oxide.

In an embodiment, wherein the polyethylene-based polymer matrix is a high-density polyethylenebased polymer matrix. One advantage of the use of high-density polyethylene is that it is known to be suitable for hydrogen applications, such as for hydrogen transport pipes.

The HDPE may typically have an average molecular weight in the range of 50,000 to 1,000,000 Da, such as 100,000 to 250,000 Da. The HDPE may have a melt flow rate in the range of 0.01 to 5 g/10 min, for instance 0.1 to 4 g/10 min or 0.5 to 2 g/10 min, as determined according to ISO1133 at 190 °C with an applied weight of 2.16 kg. As is well known in the field of polymer processing, different techniques of manufacturing parts using HDPE typically work best with HDPE different melt flow rates, respectively. For instance, HDPE having melt flow rates in the lower end of the mentioned ranges, such as 0.1 to 1 g/10 min, may be more suitable for techniques where a higher viscosity is preferred, such as extrusion, while, for instance, HDPE in the higher end of the mentioned ranges, such as 1 to 4 g/10 min, may be more suitable for other techniques where are lower viscosity is preferred, such as injection moulding. The polymer-based composite material according to the present patent disclosure shows the beneficial effects, such as that of a reduced hydrogen permeation compared to bare HDPE, for HDPE in general, including HDPE with the melt flow rates mentioned above.

The polymer-based composite material according to any one of the proceeding claims, wherein the reduced graphene oxide comprises oxygen in the range of 0.1 to 50 wt%.

According to a second aspect, there is provided hydrogen carrier for hydrogen storage and/or transport, the hydrogen carrier comprising- a hollow body comprising a polymer-based graphene composite material comprising a polyethylene-based polymer matrix and reduced graphene oxide in an amount of 0. 1 %- 15 % in weight per weight of the polyethylene-based polymer matrix.

The provided hydrogen carrier for hydrogen storage and/or transport comprises the polymer-based composite material according to the first aspect which shows a reduced hydrogen permeability compared to the bare polyethylene-based polymer. The hollow body being comprised of the polymer- based composite material thus reduced the hydrogen leakage towards the outer surface of the hollow body.

The hydrogen carrier may additionally or alternatively be referred to as a hydrogen transport carrier and/or hydrogen storage carrier.

The hollow body can additionally provide a pathway for conducting electricity and thus reduces the chance of discharges towards a hydrogen rich environment when the assembly is in use.

In an embodiment, the hollow body is made of the polymer-based graphene composite material.

In an embodiment, the hollow body is a tank, a vessel, a pipe, a joint, or a cylinder.

In an embodiment, the hydrogen carrier is a hydrogen storage container or a hydrogen transport carrier, In an embodiment, the hydrogen storage container is a hydrogen storage tank, a hydrogen storage vessel, or a hydrogen cylinder.

In an embodiment, the hydrogen cylinder is a hydrogen gas cylinder.

In an embodiment, the hydrogen transport carrier is a hydrogen transport pipe or a joint for joining hydrogen transport pipes.

In an embodiment, the polymer-based composite material is the polymer-based composite material according to any embodiment of the first aspect and/or any embodiment described below.

In an embodiment, the hollow body is a first hollow body; and the hydrogen carrier further comprises a second hollow body concentrically arranged relative to the first hollow body.

In an embodiment, the second hollow body is a hollow mechanical reinforcement body.

In an embodiment, the hydrogen carrier may further comprise a third hollow body arranged in between the first hollow body and the second hollow body.

In an embodiment, at least one of the second and third hollow bodies is a hollow mechanical reinforcement body. Any of the additional hollow bodies may add mechanical strength and/or stability to the hydrogen carrier. For instance, the hydrogen carrier may have to withstand conditions during pipe laying and also during use with, for instance, high pressure hydrogen gas.

In an embodiment, the second hollow body is made of the polymer-based composite material.

In an embodiment, the second hollow body is arranged inside the first hollow body.

In an alternative embodiment, the first hollow body is arranged inside the second hollow body.

According to a third aspect, there is provided a method for manufacturing a hydrogen carrier according wherein the hydrogen carrier is manufactured using extrusion or injection moulding.

In an embodiment, the hydrogen carrier for hydrogen storage and/or transport is the hydrogen carrier for hydrogen storage and/or transport according to any embodiment of the second aspect and/or any embodiment described below.

According to a fourth aspect, there is provided an extruded hydrogen carrier comprising or consisting of a polymer-based composite material comprising a polyethylene-based polymer matrix and reduced graphene oxide in an amount of 0.1 %- 15% in weight per weight of the polyethylene-based polymer matrix.

It will be understood that technical advantages and effects associated with features and/or embodiments of one aspect, apply to the corresponding, similar or equivalent features and/or embodiments the other aspects. It will also be apparent that the features of the various aspects and/or embodiments thereof may be applied to the other aspects and/or embodiments thereof.

Brief Description of the Drawings

The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present disclosure. The above and other advantages of the features and objects of the disclosure will become more apparent, and the aspects and embodiments will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which: Figure la is a schematic drawing of an embodiment of the assembly according to the present patent disclosure;

Figure lb is a schematic drawing of another embodiment of the assembly according to the present patent disclosure;

Figure 1c is a schematic drawing of an embodiment of the assembly according to the present patent disclosure;

Figure Id is a schematic drawing of an embodiment of the assembly according to the present patent disclosure;

Figure 2 is a schematic drawing of one embodiment of the polymer-based composite material of the present patent disclosure;

Figure 3 is a graph of H2 permeability [mol-m ^s ^MPa ¹] as a function of graphene concentration [wt%] in different polymer-based composite materials of the present patent disclosure; and

Figure 4 is a graph of volume resistivity [ohrn-cm] as a function of graphene concentration [wt%] in different polymer-based composite materials of the present patent disclosure.

Abbreviations

GO - graphene oxide;

HDPE - high density polyethylene;

LB - lithium bis(salicylate)borate;

NC - nanoclay; rGO - reduced graphene oxide; and

PE - polyethylene.

Detailed description

Carriers for carrying or being in contact with hydrogen, such as storage containers and transport pipes and pipe joints, such as tanks, vessels, cylinders, etc. have requirements in terms of thermal endurance, mechanical strength, and gas permeability. Examples of storage containers include tanks, vessels, cylinders, cartridges, canisters, cages, and caves. Assemblies for hydrogen storage and/or transport as used herein can be open- or close-ended, it can also be open at one end but closed at the other.

Graphene is a 2-dimensional carbon material. Graphene is a layered material in the form of flakes or sheets. Graphene comprises at least 30 at% carbon, has a hexagonal lattice and a thickness 1-20 times the size of a carbon atom. In the present patent disclosure, reduced graphene oxide (rGO) is used in the composite materials. In one embodiment of the present patent disclosure the composite material comprises salts, such as Li- salts, or Li -borate salts. In one embodiment the composite material comprises a graphene material as disclosed in WO 2019/054931, such as graphene composites comprising lithium bis(salicylate)borate. WO 2019/054931 is hereby incorporated by reference in its entirety.

A hydrogen carrier 100 according to the present patent disclosure comprises a hollow body that is able to withstand mechanical stress and hence provides load bearing support to the hydrogen carrier 100. The hollow body may, for instance, have a thickness in the cm size range and is as such typically a main part of the hydrogen carrier 100, or one of the main parts.

In a first aspect of the present patent disclosure there is provided a hydrogen carrier 100 for hydrogen storage and/or transport. The hydrogen carrier 100 comprises a hollow body 101 comprising or consisting of a polymer-based graphene composite material 200. The polymer-based composite material 200 comprises a polyethylene-based polymer matrix 202 and reduced graphene oxide 201 in an amount of 0. 1%- 15% in weight per weight of the polyethylene-based polymer matrix 202.

In the polymer-based composite material 200 the reduced graphene oxide 201 may be distributed in the polymer matrix 202. The polymer-based composite material 200 may also be referred to as the polymer- graphene composite material 200.

Figure la shows a schematic illustration of a hydrogen storage container 100, an embodiment of the hydrogen carrier, according to the present patent disclosure. Such a container 100 can be used to store and/or transport hydrogen. Figure la shows a schematic longitudinal cross-section of a hydrogen storage container 100 that is open-ended, e.g. in the form of a tube or pipe. Figure lb shows a crosssection along A-A of the hydrogen storage container 100 illustrated in Figure la.

In certain embodiments, the hydrogen carrier 100 may have more parts or layers such as an additional outer or inner layer that is separate from the hollow body 101. In the hydrogen carrier 100 at least the hollow body 101 comprises the polymer-graphene composite material 101. As will be discussed in more detail further down, the hollow body 101 may for example be formed by extrusion.

As mentioned, the hydrogen carrier 100 may comprise other parts, for example, but not limited to, additional cross-sectional portions as schematically illustrated in Figure 1c and d. In Figure 1c an outer portion 102, or second hollow body 102 arranged concentrically with the hollow body 101, is provided for providing increased mechanical stability or impact protection, for example. Such an outer portion 102 may comprise or consist of a carbon fiber polymer composite or steel. Similar portions as the outer portion 102 may be provided on the inside of the hollow body 101. A further alternative is that reinforcements are provided in the polymer-graphene composite material 200, for example the polymer-graphene composite material may further comprise carbon fibers. A yet further alternative is illustrated in Figure Id, wherein the hydrogen carrier comprises from outside towards inside: have a first hollow body 101’, a hollow mechanical reinforcement body 103, and a second hollow body arranged within the mechanical reinforcement body 103. At least one of the first hollow body 101’ and the second hollow body 101” comprises or consist of the polymer-graphene composite material 200. The first 101’ and second 101” hollow bodies may have a thickness in the cm size range and are typically thicker than the hollow mechanical reinforcement body 103 that would, for instance, have a thickness in the mm size range. The mechanical reinforcement body 103 may, for example, be made of stainless-steel, or made by carbon-fiber winding.

The polymer-graphene composite material 200 is schematically illustrated in Figure 2. As can be seen in the Figure the rGO 201 is homogeneously or almost homogenously distributed throughout the polymer matrix 202. Without being bound by any theory, it is believed that the homogenous distribution of graphene 201 in the polymer matrix 202 is beneficial in terms of gas permeability. In other words, a lower gas permeation can be achieved for a polymer-graphene composite material 200 wherein the rGO 201 is distributed throughout the polymer matrix 202 as compared to a polymer-based composite material wherein the rGO is more lumped together in parts of the composite material while less present in other parts of the composite material.

The polymer matrix 202 is made of a type of polyethylene (PE). Polyethylene (PE) is a group of polymers that are widely used. It accounts for over a quarter of the world’s total plastic market. Most types of polyethylene have the general chemical formula (CSPE),,. Examples of polyethylene include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polyethylene terephthalate (PET). It can be processed using standard manufacturing techniques such as extrusion, blow moulding, rotational moulding, and injection moulding. In one embodiment the polymer-graphene composite material 200 comprises HDPE.

The hydrogen carrier 100 beneficially increases the amount of hydrogen that remains in the container 100 and reduces the amount of hydrogen permeating through the hollow body 101. Additional improved properties by a hydrogen carrier 100 according to the invention include increased conductivity, increased load bearing capacity, and reduced electrostatic effects. As discussed earlier the hydrogen carrier 100 as discussed herein can be any type of container that is used to store and/or transport hydrogen in liquid and/or gaseous form. Examples includes tanks, vessels, pipes, joints, cylinders, cartridges, etc.

The hydrogen carrier 100 typically is configured to withstand both a wide range of temperatures and high pressure. For instance, in hydrogen transport, the hydrogen may be transported at pressures ranging from 1 bar to 100 bar, for instance 2 to 30 bar. Hence, the associated assemblies will be subjected to substantial mechanical load. The hollow body 101 may be configured to withstand pressures within these ranges. Polyethylene based pipelines may be used preferably in the lower range of hydrogen pressures, such as at 2-10 bar or 2-5 bar.

As discussed, the polymer-graphene composite material 200 comprises rGO 201 distributed in the polymer matrix 202. The amount of rGO in a polymer-graphene composite material 200 is 0.1-15 % in weight per weight of the polymer, 0.5-9 % in weight per weight of the polymer, 0.5-5.5 % in weight per weight of the polymer, 2.5-5% in weight per weight of the polymer, 3.8-5.5 % in weight per weight of the polymer, or 3-5 % in weight per weight of the polymer. The rGO can comprise graphene from any type of graphene source. The rGO may comprise 0.1-50 wt% of oxygen.

Figure 3 shows measured hydrogen gas permeabilities of different polymer-based composites according to the present patent disclosure versus the amount of additive in wt% added to the polymer matrix. In Figure 3, results for several graphene-polymer composite materials 200 are shown, each comprising high density polyethylene (HDPE) and reduced graphene oxide (rGO). All samples were manufactured using twin screw extrusion and had the same thickness.

Samples with a first type polymer-based composite material shown in Figure 3 were manufactured using a first grade of HDPE suitable for extruding. These samples are indicated with by “Gl”. The first grade of HDPE had a melt flow rate of about 0.5 g/10 min as measured according to ISO 1133 with a weight of 2.16 kg and at 190 °C. Samples with a second type of polymer-based composite material were manufactured using a second grade of HDPE, suitable for injection moulding. These samples are indicated with “G2” The second grade of HDPE had amelt flow rate of about 2.0 g/10 min as measured according to ISO 1133 with a weight of 2.16 kg and at 190 °C. Figure 3 further shows the gas permeability for polymer-based composite materials comprising high density polyethylene (HDPE) and reduced graphene oxide comprising lithium bis(salicylate)borate (LB), indicated as “HDPE LB”, and a mixture of reduced graphene oxide comprising lithium bis(salicylate)borate and nanoclays (NC), which is indicated as “HDPE LB-NC”. In both these cases, the second grade of HDPE was used. The additive concentration indicates the total wt% of additive added to the HDPE polymer matrix. As can be seen in the figure, all polymer-based composite materials comprising a graphene additive, i.e. rGO, NC, or rGO comprising lithium bis(salicylate)borate exhibit a lower H₂-gas permeability compared to the bare HDPE polymer samples with 0 wt% additive concentration. Although samples with the G2 grade HDPE appear to perform somewhat better than the samples with the G1 grade HDPE, all samples show an improved hydrogen permeability when the additives are included, irrespective of what grade of HDPE is used. The higher the concentration of additive the lower the H₂ gas permeability for all composite materials. The best performing composite materials in terms of hydrogen permeability are the HDPE G2 rGO and HDPE LB samples. The HDPE LB-NC sample is performing similar to or better than the HDPE G1 rGO sample.

However, increasing the amount of rGO additive too much is no longer beneficial since it will have reduce the processibility of the polymer-based composite material. For example, the higher the rGO concentration, the higher the polymer viscosity and, hence, the more difficult to processes. Furthermore, increasing the graphene concentration in polymer composites is known to reduce the flexibility of the polymer. A large amount, more than 15% in weight per weight of the polymer, of graphene additive results in a material that is not possible or very difficult to process in standard techniques such as injection moulding, blow moulding and extrusion.

As mentioned above the rGO in a composite material 200 according to the present patent disclosure may be any type of rGO, or any type of graphene that has been first oxidized and then reduced to form rGO. rGO is a form of graphene oxide (GO) that is processed in order to reduce the oxygen content. The processing can be by chemical, thermal, or other methods known to persons skilled in the art.

In one embodiment the polymer-based composite material 200 comprises a mixture of nanoclay and graphene. Nanoclays may comprise or be layered mineral silicates. The nanoclay may comprise, or consist of, layered mineral silicate-based nanoparticles. There are several types of nanoclays that are classified depending on chemical composition and morphology: montmorillonite, bentonite, kaolinite, hectorite, and halloysite. In one embodiment of the present patent disclosure the polymer-based composite material comprises a mixture of nanoclay and reduced graphene oxide as additives. The amount in terms of weight of nanoclay and reduced graphene oxide may be equal, or almost equal. Herein the term ‘equal’ refers to a difference of 10% or less.

In one embodiment of the invention the rGO comprises a salt, the salt may be intercalated in between the graphene layers. The salt may comprise Na⁺ or Li⁺. The salt may further comprise Al or B as anion. In one embodiment the salt comprises or is lithium bis(salicylate)borate (Li[BScB]). The rGO in the composite material 200 may further comprise Li⁺ and/or Na⁺. This is beneficial in terms of reduced hydrogen permeability, as is clear from Fig. 3 from the samples including “LB”. Without being bound by any theory, Li⁺ and/or Na⁺ have a high capacity as a hydrogen storage material wherein hydrogen can be reversible stored at the material. Additionally, pristine graphene and reduced graphene oxide are also able to reversibly store hydrogen. The combination of reduced graphene oxide and Li⁺ and/or Na⁺, a highly hydrogen impermeable composite material is obtained. This can be seen in the data of Figure 3. As for all types of additives used in the present patent disclosure, also in this case the hydrogen gas permeability value decreases with an increased concentration of additive. The composite material with the lowest measured hydrogen permeability is the composite material comprising rGO and lithium bis(salicylate) borate (“HDPE LB”).

Another benefit of the hydrogen carrier 100 is that it may have a low volume or electrical resistivity. This resistivity is a material property that measures how well a material resists electrical current, the unit for volume resistivity is ohm-centimetre [Q-cm] or ohm-meter [Q-m], Figure 4 shows the volume resistivity as a function of rGO content in wt% in a polymer-based composite material 200 according to the present patent disclosure. As can be seen in the Figure an increasing amount of rGO result in a decreasing resistivity. The resistivity decreases rapidly to a value that is close to 0 between an addition of 3 wt% and 4 wt% rGO, more specifically between 3.3 wt% and 3.8 wt%.

The hydrogen carrier 100 according to the present patent disclosure can typically be manufactured by standard techniques such as injection moulding, rotational moulding, blow moulding or spray coating. In one aspect there is provided a method for manufacturing a hydrogen carrier 100 according to the present patent disclosure, wherein the hydrogen carrier 100 is manufactured using extrusion or injection moulding.

Extrusion of polymers is a processing technique wherein the polymer is melted and formed into a desired profile. The polymer is melted by heaters and by mechanical energy generated by screws used in the process. The polymer-graphene composite material 200 may be manufactured by mixing a polymer with rGO using for example an extruder.

Experimental

For all sample preparations HDPE was used as the polyethylene-based polymer. These samples thus contained a HDPE-based polymer matrix.

Gas permeability testing

Four different samples were prepared, as mentioned above with respect to Fig. 3. Further details are described below. For the LB-NC samples a 50/50 ratio in terms of weight of LB/NC was used. Preparation of samples with rGO as additive

A batch of HDPE comprising 11 weight% of rGO was first prepared. Thereafter, this batch was diluted to concentrations of 0.5, 0.66, 2.75, 3.0, 3.3, 3.85, 5.0, 5.5, 6.93, and 7.4 weight% through mixing with more HDPE.

Mixed samples including the HDPE LB and LB-NC samples

The mixed samples were prepared using the 11 weight% rGO batch. This 11 wt% batch was diluted and then extruded to the desired concentrations of additive including rGO and LB and optionally NC. The extrusion was performed using standard process parameters. The samples including LB comprised 10 wt% of lithium bis(salicylate)borate relative to rGO.

Table 1 below shows an overview of all samples prepared for the gas permeability tests.

Table 1. Overview of samples.

Gas permeability testing

The gas permeability was tested according to the ASTM D3985-17 method. The permeability curves were obtained by placing them in a circular permeation cell. A porous stainless-steel plate was applied to support the sample during the high-pressure conditions. The area of the stainless-steel plate was 19.6 cm², which area was used for the permeability calculations as the effective area available for permeation. The sealing between the feed and permeate side was obtained by an O-ring that was placed between the sample and the feed side of the module. An additional sealing ring, placed on the permeate side of the module, was used to prevent leakages towards the external environment.

Permeation measurements were conducted using a constant-pressure method, analogue to ASTM D3985 -17. The set-up was designed to withstand a pressure up to 30 bar. The permeation cell was placed in a Memmert UF450 forced air circulation oven for temperature control.

The permeation experiments were performed as follows:

1. Seal sample in cell and connect it to the setup.

2. Heat the setup to the operating temperature (50 °C) and exposing to small overpressure ofN₂ (1 bar).

3. At a stable temperature/pressure and gas chromatography analysis, N₂ is replaced with H₂, while the pressure is rapidly increased to 20 bar. H₂ gradually permeates through the sample, and the breakthrough is determined by gas chromatography. The permeation is left to stabilize to obtain the permeate rate at a temperature of 50 °C.

Results gas permeability testing

Figure 3 shows a permeability graph wherein H₂ permeability is measured for samples comprising HDPE and rGO, HDPE and a mixture of rGO comprising lithium bis(salicylate)borate and nanoclay (• • •), and HDPE and rGO comprising lithium bis(salicylate)borate. As can be seen for all samples a decreased permeability can be seen with increasing concentrations of reduced graphene oxide. What can also be seen is that the materials comprising lithium bis(salicylate)borate show the lowest gas permeability for H₂.

The lowest gas permeability of the three samples is shown by the material comprising graphene and lithium bis(salicylate)borate and no nanoclays.

Resistivity testing

Six samples were tested for resistivity: HDPE comprising 0.66, 3.3, 3.85, 5.5, 6.93, and 131 wt% rGO. The electrical resistivity was derived through a series of measurements and calculations on respective filaments produced with extrusion. First, a linear relationship between the measured resistance and the resistivity value was established by measuring the resistance up to 1 m, using 10 cm intervals, and then deriving the resistivity value by calculating the gradient of the resistance vs length plot. Linearity was established, so the resistivity values were calculated for 10 cm length filaments. For the contact areas between the filament and the probe (Electron Microscopy Sciences, USA), silver colloidal paste was used for the contact areas between the filament and the probe. The resistance was measured using a four probe micro-ohmmeter. The results from the resistivity testing are shown in Figure 4. The results have been discussed above.

Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent to those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below.

Claims

1. A polymer-based composite material (200) comprising a polyethylene-based polymer matrix (202) and reduced graphene oxide (201) in an amount of 0.1 %- 15% in weight per weight of the polyethylenebased polymer matrix (202).

2. The polymer based composite material (200) according to claim 1, wherein the reduced graphene oxide (201) is distributed in the polyethylene-based polymer matrix (202).

3. The polymer-based composite material (200) according to claim 1 or 2, comprising reduced graphene oxide (201) in an amount of 0.5%-9% in weight per weight of the polyethylene-based polymer matrix (202).

4. The polymer-based composite material (200) according to claim 1, 2 or 3, wherein the amount of reduced graphene oxide (201) in the polymer-based composite material (200) is 0.5%-5% in weight per weight of the polyethylene-based polymer matrix (202).

5. The polymer-based composite material (200) according to any one of the preceding claims, wherein the amount of reduced graphene oxide (201) in the polymer-based composite material (200) is 2.5%-5% in weight per weight of the polyethylene-based polymer matrix (202), preferably 3%-5% in weight per weight of the polyethylene-based polymer matrix (202).

6. The polymer-based composite material (200) according to any one of the proceeding claims, wherein the polymer-based composite material further comprises nanoclay.

7. The polymer-graphene composite material (200) according to claim 6, wherein the polymer-based composite material comprises the nanoclay in an amount equal to 90 to 110 wt% per weight of reduced graphene oxide.

8. The polymer-graphene composite material (200) according to claim 6 or 7, wherein the nanoclay comprises layered mineral silicate-based nanoparticles.

9. The polymer-graphene composite material (200) according to claim 8, wherein the layered mineral silicate-based nanoparticles comprise one or more selected from the group consisting of montmorillonite nanoparticles, bentonite nanoparticles, kaolinite nanoparticles, hectorite nanoparticles, halloysite nanoparticles.

10. The polymer-based composite material (200) according to any one of the proceeding claims, wherein the reduced graphene oxide (201) in the polymer-based composite material (200) comprises a Li-salt, preferably lithium bis(salicylate)borate.

11. Hydrogen carrier (100) for hydrogen storage and/or transport, the hydrogen carrier comprising a hollow body (101) comprising a polymer-based graphene composite material (200) according to any one of claims 1 to 10.

12. Hydrogen carrier (100) according to claim 11, wherein the hollow body is a tank, a vessel, a pipe, a joint, or a cylinder.

13. Hydrogen carrier (100) according to claim 11 or 12, wherein the hydrogen carrier is a hydrogen storage container or a hydrogen transport carrier, wherein preferably the hydrogen storage container is a hydrogen storage tank, a hydrogen storage vessel, or a hydrogen cylinder wherein optionally the hydrogen cylinder is a hydrogen gas cylinder; and/or the hydrogen transport carrier is a hydrogen transport pipe or a joint for joining hydrogen transport pipes.

14. Hydrogen carrier (100) according to claim 11, 12 or 13, wherein the hollow body (101) is made of the polymer-based graphene composite material (200).

15. Hydrogen carrier (100) according to any one of claims 11 to 14, wherein the hollow body (101) is a first hollow body (101’, 101”); and the hydrogen carrier further comprises a second hollow body (101’, 101”) concentrically arranged relative to the first hollow body (101’, 101”).

16. Hydrogen carrier (100) according to claim 15, further comprising a hollow mechanical reinforcement body (103) arranged in between the first hollow body (101’, 101”) and the second hollow body (101’, 101”)

17. Hydrogen carrier (100) according to claim 15 or 16, wherein the second hollow body (101’, 101”) is made of the polymer-based composite material (200).

18. Hydrogen carrier (100) according to claim 15, 16 or 17, wherein the second hollow body (101”) is arranged inside the first hollow body (101’).

19. Hydrogen carrier (100) according to any one of claims 15 to 18, wherein the first hollow body (101”) is arranged inside the second hollow body (101’).

20. A method for manufacturing a hydrogen carrier (100) according to any one of claims 11 to 19, wherein the hydrogen carrier (100) is manufactured using extrusion or injection moulding.

21. An extruded hydrogen carrier (100) comprising a polymer-graphene composite material (200) according to any one of claims 1 to 10.