Integrated materials and methods for integrated operation of hydride storage systems

Abstract

To provide a metal hydride based composite material for hydrogen storage that effectively controls the heat generated during hydrogen absorption and consumed during hydrogen desorption in hydrides, and a method of operating a hydride based system for hydrogen storage that is less complex and less costly than conventional systems.SOLUTION: A composite material for hydrogen storage comprising a powder or pellets of a hydride and a phase changing material (PCM), in which the PCM is an encapsulated phase changing material (EPCM) which is homogeneously dispersed within the powder or pellets of the hydride.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to composite metal hydride-based hydrogen storage materials and methods of operating metal hydride-based hydrogen storage systems capable of releasing and absorbing hydrogen, which can be used as fuel sources for fuel cells. [Background technology]

[0002] Hydrogen is used in many industrial sectors, for example as a fuel for fuel cells or heat engines, for example as a reagent in hydrogenation reactions, or as a source for storing energy, for example in batteries.

[0003] The debate over a future, environmentally and economically viable energy economy has in recent years also increasingly focused on efficient solutions for energy generation. Developments are being carried out in various technological fields, for example in the field of combined heat and power for industrial or domestic use, or in the automotive sector, with the aim in each case to increase the efficiency of the entire process.

[0004] In the power generation field, the potential of fuel cell technology has been recognized for several years, and efforts have been made to efficiently generate and utilize electricity and the heat derived from it. A fuel cell is a galvanic cell that converts the chemical reaction energy of a continuously supplied fuel and oxidant, and the heat generated by the reaction, into electrical energy. Hydrogen is often used as the fuel and oxygen as the oxidant.

[0005] Hydrogen storage is a key technology enabling the development of a hydrogen and fuel cell-based economy. Hydrogen has the highest energy density per unit mass of any fuel; however, its volumetric density at ambient temperature and pressure is low, resulting in a rather low energy density per unit volume. The most common hydrogen storage method remains compressing and storing hydrogen gas at pressures of approximately 35 MPa to 75 MPa, but this method has many drawbacks. Tanks are expensive, and their structures have proven susceptible to aging. Furthermore, due to the inherent limitations of compressed hydrogen density, improvements in this technology have been limited. Another storage method involves liquefying hydrogen in cryogenic tanks at extremely low temperatures. These tanks also require high insulation, which adds to their cost.

[0006] In recent years, hydrogen storage in the form of metal hydrides has been investigated as an advantageous alternative that offers safer storage conditions and limited energy expenditure. Hydride storage systems, especially metal hydride storage systems, have proven particularly suitable for fuel storage. Solid-state hydrogen storage, for example via MgH2, offers very good performance in terms of volumetric density. Metal hydride storage systems function at very low operating pressures, making them safe and compact. Storing fuels such as hydrogen in metal hydrides allows for near-loss-free storage over long periods of time without additional energy expenditure, as the gas is chemically bound. From a safety perspective, metal hydride storage systems are also preferable to compressed gas or liquid hydrogen storage systems, as hydrogen cannot escape explosively.

[0007] Research into metal hydride materials has focused on improving the volumetric and gravimetric capacities, hydrogen absorption / desorption kinetics, and reaction thermodynamics of potential material candidates. Furthermore, the impact of long-term cycling must be considered when developing hydrogen-based technologies. Transition metal additives have been used to improve hydrogen absorption / desorption kinetics, as disclosed, for example, in W. Oelerich, T. Klassen, and R. Bormann, "Metal oxides as catalysts for improved hydrogen sorption in nanocrystalline Mg-based materials," Journal of Alloys and Compounds, Vol. 135, pp. 237-242, 2001.

[0008] Other approaches to improving both the hydrogen absorption / desorption reaction kinetics and reaction thermodynamics of metal hydrides focus on thermal management of heat transfer during hydrogen desorption and absorption. One reason for this is that dehydrogenation, i.e., the release of hydrogen from a hydride, is an endothermic reaction that requires heat, while hydriding, i.e., the absorption of hydrogen in a hydride storage, is an exothermic reaction that generates heat. For some reactions, such as magnesium hydride (ΔH: approximately −75 kJ / mol), significant efforts must be made to manage heat so that the desorption / absorption reactions occur at the desired reaction rate.

[0009] US Patent Application Publication No. 2010 / 0266488 proposes a hydrogen storage material based on magnesium hydride and graphite, preferably expanded natural graphite (ENG), in a compressed form that is said to have good properties in terms of mechanical strength and thermal conductivity, thereby exhibiting good absorption and desorption kinetics.

[0010] M. Jehan and D. Furchart, "McPhy-Energy's proposal for solid-state hydrogen storage materials and systems," Journal of Alloys and Compounds, (2013), No. 580, pp. S343-S348 (Non-Patent Document 2), propose using in-tank heat storage in addition to expanded natural graphite (ENG) as a heat transfer agent by filling a coaxial tube with a phase change material (PCM) to manage the bulk of the heat in the Mg / MgH2 reaction. The PCM melts during hydrogenation and stores energy as latent heat of fusion. During hydrogen desorption, the PCM solidifies and provides thermal energy to the hydride, which can then be liberated by decomposition.

[0011] US Patent Application Publication No. 2012 / 006397 (Patent Document 2) discloses an insulated metal hydride-based hydrogen storage tank consisting of a hydride vessel and a tubular vessel incorporating a phase change material (PCM).

[0012] However, it was found that heat transfer between the hydride bath and the PCM was not very effective, especially in the later stages of each reaction when the PCM was more than half molten or solidified, resulting in heat transfer problems. For this reason, and due to the increased weight and volume, the proposed solution was not well accepted in the market. Another problem was that the use of PCM required the construction of a separate bath, piping, etc., which made the system complicated. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] US Patent Application Publication No. 2010 / 0266488 [Patent Document 2] US Patent Application Publication No. 2012 / 006397 [Non-patent literature]

[0014] [Non-Patent Document 1] W. Oelerich, T. Klassen, and R. Bormann, "Metal oxides as catalysts for improved hydrogen sorption in nanocrystalline Mg-based materials," Journal of Alloys and Compounds, 2001, No. 135, pp. 237-242 [Non-patent document 2] M. Jehan and D. Furchart, "McPhy-Energy's proposal for solid-state hydrogen storage materials and systems," Journal of Alloys and Compounds, (2013), No. 580, pp. S343-S348 [Non-patent document 3] K. Pielichowska and K. Pielichowski, "Phase changing materials for thermal energy storage," Progress in Materials and Science (2014), No. 65, pp. 67-123 [Non-patent document 4] M. Farid, A. Khudhair, S. Razak, and S. Al-Hallaj, "A review on phase change energy storage: materials and applications," Energy Conversion and Management (2004), No. 45, pp. 1597-1615 [Non-Patent Document 5] S. Sundarram et al., “The effect of pore size and porosity on thermal management performance of phase change material infiltrated in microcellular metal foams,” Applied Thermal Engineering, 2014, No. 64, p. 147-154. [Non-patent document 6] B. Sakintuna et al., "Metal hydride materials for solid hydrogen storage: A review," International Journal of Hydrogen Energy, No. 32, (2007), pp. 1121-1140 [Non-Patent Document 7] V. Kumar et al., "Hydrogen absorption / desorption characteristics of room temperature ZrMn2‐XNiX system (X=1.25-1.50)," Bull. Mater. Sci., No. 37, pp. 655-660, 2014 Summary of the Invention [Problem to be solved by the invention]

[0015] It is an object of the present invention to provide a hydride-based composite hydrogen storage material that effectively manages the heat generated during hydrogen absorption and dissipated during hydrogen desorption in the hydride, and a hydride-based hydrogen storage system that is less complex and less costly than known systems.

[0016] The object is achieved by a composition having the features set forth in claim 1. Preferred embodiments are set forth in the dependent claims. [Means for solving the problem]

[0017] According to one aspect of the present invention, there is provided a composite material comprising a metal hydride powder or pellets and a phase change material (PCM). In this aspect, the PCM is an encapsulated phase change material (EPCM) uniformly dispersed in the hydride powder or pellets. In another embodiment of the present invention, the encapsulated phase change material (EPCM) is a microencapsulated phase change material (MEPCM).

[0018] Encapsulated Phase Change Material Encapsulated phase change materials (EPCMs) are described in K. Pielichowska and K. Pielichowski, "Phase changing materials for thermal energy storage," Progress in Materials and Science (2014), No. 65, pp. 67-123 (Non-Patent Document 3), and M. Farid, A. Khudhair, S. Razak, and S. Al-Hallaj, "A review on phase change energy storage: materials and applications," Energy Conversion and Management (2004), No. 45, pp. 1597-1615 (Non-Patent Document 4), which are incorporated herein by reference in their entireties. Encapsulated phase change materials (EPCMs) can be described as particles containing a phase change material (PCM) surrounded by a shell or coating, or as particles embedded in a particulate matrix such that upon melting, the PCM remains embedded in the matrix particles. Such PCM materials are sold under the trade names of Rubitherm (registered trademark) RT series or Rubitherm (registered trademark) SP series by Rubitherm Technologies AG of Germany, and have a wide melting point range from -10°C to 90°C. Suitable PCM materials include Rubitherm® RT100, Rubitherm® RT100HC, Rubitherm® RT90HC, Rubitherm® RT80HC, Rubitherm® RT82, Rubitherm® RT70HC, Rubitherm® RT69HC, Rubitherm® RT65, Rubitherm® RT64HC, Rubitherm® RT62HC, Rubitherm® RT60, Rubitherm® RT55, Rubitherm® RT54HC, Rubitherm® RT50, Rubitherm® RT47, Rubitherm® RT44HC, Rubitherm® RT42,Rubitherm® RT35HC, Rubitherm® RT31, Rubitherm® RT28HC, Rubitherm® RT24, Rubitherm® RT22HC, Rubitherm® RT21HC, Rubitherm® RT21, Rubitherm® RT18HC, Rubitherm® RT15, Rubitherm® RT12, Rubitherm® RT11HC, Rubitherm® RT10HC, Rubitherm® RT10, Rubitherm® RT9, Rubitherm® RT8HC, Rubitherm® RT8, Rubitherm® RT5HC, Rubitherm® RT5, Rubitherm® RT4, Ru Examples of suitable heat-resistant curing agents include, but are not limited to, Rubitherm® RT3HC, Rubitherm® RT2HC, Rubitherm® RT0, Rubitherm® RT-4, Rubitherm® RT-9HC; Rubitherm® SP90, Rubitherm® SP70, Rubitherm® SP58, Rubitherm® SP50, Rubitherm® SP31, Rubitherm® SP29EU, Rubitherm® SP26E, Rubitherm® SP25E2, Rubitherm® SP24E, Rubitherm® SP21EK, Rubitherm® SP15, Rubitherm® SP-11, and Rubitherm® SP-17.

[0019] A variety of encapsulation techniques may be used to prepare capsules, particularly microcapsules, with a polymer or metal cover and a PCM core. Methods employed to prepare capsules with a polymer cover and a PCM core include complex coacervation, suspension, emulsion, condensation, addition polymerization, or spray coating. A metal cover may be disposed around the PCM material or around the polymer-encapsulated PCM material.

[0020] Other suitable encapsulated PCM materials are sold by Croda under the trade name CrodaTherm™ ME29P by Croda International Ltd., UK; savE® FS29 by Pluss Advanced Technologies Ltd., India; and Puretemp® 151, Puretemp® 108, Puretemp® 68 by Puretemp Ltd., USA.

[0021] Generally, the diameter of PCM particles ranges from 1 μm to 5 mm, preferably from 1 μm to 1 mm. Microencapsulated phase change materials (MEPCMs) are described as particles containing a core material surrounded by a coating or shell, or embedded in a matrix, with particle diameters ranging from about 1 μm to less than 1000 μm, preferably from about 10 μm to about 20 μm.

[0022] In another embodiment, the encapsulated phase change material is contained within the pores of a particulate porous or structured sponge-like matrix material. This type of material is often referred to as a PCM composite or shape-stabilized PCM (ss-PCM). Such EPCM particles are available from Rubitherm Technologies, Germany, under the trade names Rubitherm® PX15, Rubitherm® PX25, Rubitherm® PX52, Rubitherm® PX82, Rubitherm® GR42, and Rubitherm® GR82. Thus, for purposes of the present invention, the term encapsulated phase change material (EPCM) is intended to encompass a PCM material embedded in a particulate matrix material.

[0023] The diameter of the particles contained in the pores of the porous or structured sponge-like matrix material containing the phase change material in particulate form is also generally in the range of 1 μm to 5 mm, preferably 1 μm to 1 mm. However, the pore size of the pores or channels containing the PCM material is more specific. Generally, the pore size of such materials is in the range of 25 nm to 250 μm, preferably 1 μm to 150 μm, and more preferably 25 μm to 100 μm. See S. Sundarram et al., "The effect of pore size and porosity on thermal management performance of phase change material infiltrated in microcellular metal foams," Applied Thermal Engineering, 2014, Vol. 64, pp. 147-154 (Non-Patent Document 5).

[0024] The heat generated when the hydrogen storage material absorbs hydrogen is stored in the phase change material and then used to supply heat to the hydride material when hydrogen is desorbed from the metal hydride. Thus, the heat generated by hydrogen absorption is stored in the phase change material when the phase change material changes from a first phase to a second phase. Then, during use, the stored heat is released when the phase change material changes from the second phase to the first phase. In one embodiment of the present invention, the phase change material (PCM) is selected to change from a solid phase to a liquid phase, or vice versa. This ensures high thermal conductivity without the need to construct a separate reservoir, piping, etc. for the PCM material.

[0025] In another embodiment of the present invention, a melting area ΔT, as determined by differential scanning calorimetry (DSC), between the hydrogen desorption temperature (T1) at the operating desorption pressure and the hydrogen absorption temperature (T2) at the operating absorption pressure of a selected metal hydride is f The phase change material (PCM) is selected so that it has a melting area ΔT of the PCM, as determined by DSC, to avoid favoring one reaction direction over the other in terms of loading or unloading time. f Peak T f It is desirable that the time T1 is as close as possible to (T1 + T2) / 2. The same is also desirable for the data on the coagulation area and the coagulation area peak determined by DSC. It is desirable that the coagulation area and the coagulation area peak are as close as possible to the melting area peak.

[0026] Metal hydrides Metal hydrides used as hydrogen storage materials are classified into different categories depending on their desorption temperatures. An overview of common metal hydrides and their properties can be found in B. Sakintuna et al., "Metal hydride materials for solid hydrogen storage: A review," International Journal of Hydrogen Energy, Vol. 32, (2007), pp. 1121-1140 (Non-Patent Document 6), which is incorporated herein by reference in its entirety.

[0027] The relationship between pressure, temperature, and hydrogen concentration in a metal during hydrogen absorption is determined as a pressure-composition-temperature (PCT) isotherm over a temperature range. Hydrogen dissolves into the metal lattice at a specific temperature during pressure increase. This process follows Sievert's law until a saturation concentration is reached (α phase). After that, the concentration in the metal increases even without pressure increase; a hydride phase (β phase) is formed; i.e., hydrogen begins to react with the metal to form metal hydrides, and α and β phases coexist in the alloy. This "plateau region" follows both van't Hoff's law and Gibbs' phase rule. At the end of the plateau region, the pressure is increased again, and hydrogen atoms dissolve into the hydride phase according to Sievert's law. The van't Hoff equation is:

[0028]

number

[0029] where P eq represents the equilibrium plateau pressure, R represents the gas constant, and T represents the reaction temperature.

[0030] To compare different hydrides, it is common to construct van't Hoff diagrams based on the equilibrium values of the PCT diagrams in the middle of the plateau region at different temperatures. eq ) to determine the enthalpy of absorption (ΔH abs ) and entropy value of the hydrogen absorption reaction. abs ) is the ln(P eq ) is calculated from the slope of the line (V. Kumar et al., "Hydrogen absorption / desorption characteristics of room temperature ZrMn2- X Ni X system (X=1.25-1.50),” Bull. Mater. Sci., Vol. 37, pp. 655-660, 2014 (see Non-Patent Document 7). Similarly, the reaction enthalpy (ΔH des) is calculated from the slope of the line obtained from the pressure-composition-temperature (PCT) curve of the hydrogen desorption reaction.

[0031] In the category of intermediate-temperature hydrides, desorption begins at 100°C to 200°C and atmospheric pressure of 100 kPa. Intermediate-temperature hydrides are those with an absolute value of the reaction enthalpy (|ΔH abs It is defined as the coefficient |. In principle, intermediate-temperature hydrides have a hydrogen storage density of approximately 2.5% to 5% by weight relative to the metal. Medium-temperature hydrides include aluminum hydrides such as NaAlH4 and amides such as LiNH2, which have a H2 absorption capacity of up to 4.5% by weight. The optimum hydrogen absorption temperature (T1) is approximately 125°C for sodium aluminum hydride, for example, and the hydrogen desorption temperature (T2) is approximately 160-185°C. The relatively high hydrogen storage capacity and relatively low operating temperatures of intermediate-temperature hydrides make them interesting candidates for mobile applications.

[0032] In the case of high-temperature hydrides, desorption begins at temperatures above 200°C and atmospheric pressures of 100 kPa. High-temperature hydrides are those in which the absolute value of the reaction enthalpy (|ΔH abs High-temperature hydrides are generally defined as a coefficient. As a rule, high-temperature hydrides have even higher hydrogen storage densities of approximately 7% to 15% by weight of hydrogen relative to the base metal or compound. High-temperature hydrides are often formed from light metals (magnesium, aluminum) and / or non-metals (nitrogen, boron) and have high capacities that make them suitable for use in fuel cells and H2 internal combustion engines. For magnesium hydride, the optimum hydrogen desorption temperature (T1) is approximately 300°C, and the optimum hydrogen desorption temperature (T2) is 340°C to 400°C.

[0033] Low-temperature hydrides, with desorption temperatures between -40°C and 100°C at 100 kPa, have a relatively low gravimetric hydrogen storage capacity of less than 2% by weight, and are therefore very clearly only useful for mobile applications, particularly for forklift and bicycle prototypes, where low storage capacity can be tolerated. Low-temperature hydrides are those with an absolute value of the reaction enthalpy (|ΔH) of the hydrogen absorption reaction of less than 30 kJ / mol H2. abs|) (coefficient).

[0034] The metal hydride powder or granules may be of any suitable particle size, for example, the average diameter of the granules may be about 1 μm or more, e.g., 1 μm to 50 mm, preferably 1 μm to 1000 μm, and more preferably 10 μm to 1000 μm. DETAILED DESCRIPTION OF THE INVENTION

[0035] As mentioned above, in embodiments of the present invention, the melting area ΔT, as determined by DSC, of a selected metal hydride is determined between the hydrogen desorption temperature (T1) at the operating desorption pressure and the hydrogen absorption temperature (T2) at the operating absorption pressure. f The phase change material (PCM) is selected so that it has a high thermal conductivity and the shell material is selected so that it can withstand the desired temperatures and contact with hydrogen without being harmed.

[0036] In general, it is preferable that the hydrogen desorption pressure is selected between 10 kPa and 2,000 kPa depending on the hydride, and the hydrogen absorption pressure, that is, the filling pressure, is selected between 150 and 10,000 kPa, preferably between 30,000 kPa or 70,000 kPa.

[0037] While polymer-encapsulated PCMs are useful for dispersing in powders or pellets of medium-temperature or low-temperature hydrides, metal-encapsulated PCMs are preferred for dispersing in powders or pellets of high-temperature hydrides to avoid shell decomposition.

[0038] The minimum amount of phase change material is required to convert the energy stored in the hydride chemical bonds into the latent heat of fusion ΔH of the PCM material. m The total energy stored in the chemical bonds of the hydride, E tot (HYD) is the enthalpy of the hydride absorption reaction, ΔH r (HYD) and the stored mass of hydrogen in the hydride m HYD This is calculated by multiplying

[0039]

number

[0040] For example, ΔH r = 25 kJ / mol H2 and an absorption capacity of 1.5 wt% (meaning that 1.5 kg of H2 can be stored for every 100 kg of storage material). 0.95 Zr 0.05 Mn 1.46 V 0.45 Fe 0.09 The melting point of PCM is about 53°C, and the latent heat of fusion ΔH m The minimum amount of CrodaTherm™ 53 with a (PCM) of 226 kJ / kg can be calculated by first determining the stored energy (E) in 100 kg of hydride (ignoring heat losses) as follows:

[0041]

number

[0042] The minimum amount of PCM per 100 kg of hydride can then be calculated based on the stored energy (E) in 100 kg of hydride and divided by the heat capacity of the PCM.

[0043]

number

[0044] Therefore, at least 82.97 kg of active CrodaTherm™ 53 PCM material is required per 100 kg of Hydralloy® C5. This calculation is provided for illustrative purposes only. Note that CrodaTherm™ 53 is not an encapsulated phase change material, but according to the present invention must be provided as such. The encapsulation or matrix embedding adds some weight (although very little volume) to this calculation.

[0045] In one embodiment of the present invention, the metal hydride and encapsulated phase change material may be in the form of a compacted material. As used hereinafter, the term compacted material refers to a material whose density is significantly higher than that of the raw material in powder form. This material is obtained in particular by compacting a mixture of powdered or granular raw materials with or without the addition of a compacting agent, thereby reducing the porosity.

[0046] In yet another embodiment, the composite of hydride powder or pellets and phase change material (PCM) may further incorporate a heat transfer enhancer, which may be selected from graphite, such as expanded natural graphite (ENG), or other known materials. In yet another embodiment, the composite material is incorporated into a hydrogen storage tank, which is preferably connected to a fuel cell.

[0047] In yet another embodiment, the present invention relates to a method of operating a metal hydride-based hydrogen storage system capable of releasing and absorbing hydrogen. The method includes providing a composite material comprising a powder or pellets of a metal hydride and a phase change material (PCM). The PCM is an encapsulated phase change material (EPCM) or a matrix-embedded phase change material (MPCM) uniformly dispersed in the hydride powder or pellets. The method also includes sequentially filling the composite material with hydrogen and evacuating it again. In one embodiment, the hydrogen is evacuated at a pressure between 10 kPa and 2,000 kPa. In another embodiment, the hydrogen is filled at a pressure between 150 kPa and 70,000 kPa, preferably between 200 kPa and 30,000 kPa.

Claims

1. A composite material consisting of a hydride powder or pellets and a phase change material (PCM), wherein the phase change material is an encapsulated phase change material (EPCM) uniformly dispersed in the hydride powder or pellets, and is in the form of particles with a diameter ranging from 1 μm to 1 mm; The minimum amount of the phase change material in the hydride powder or pellet is selected according to the following formula: m PCM =(ΔH r (HYD)・ m HYD ) / ΔH m (PCM) In the formula, m ＰＣＭ is the minimum amount of the phase change material, and ΔH ｒ (HYD) is the enthalpy of the hydrogen absorption reaction, mHYD is the mass of hydrogen stored in the hydride, and ΔH ｍ (PCM) is the latent heat of fusion of said phase change material.

2. 10. The composite material of claim 1, wherein the phase change material is a microencapsulated phase change material (MEPCM) that is uniformly dispersed in the powder or pellets of the hydride.

3. 10. The composite material of claim 1, wherein the phase change material is in the form of particles having a diameter in the range of 10 μm to 20 μm.

4. The phase change material has a melting area ΔT determined by differential scanning calorimetry (DSC) at a peak T ｆ is the hydrogen desorption temperature T １ 2. The composite material of claim 1, wherein the .lambda.

5. The phase change material has a melting area ΔT as determined by DSC. ｆ Peak T ｆ is the operating desorption pressure and the hydrogen desorption temperature T １ and at the operating desorption pressure of the hydride, the hydrogen absorption temperature T ２ 10. The composite material of claim 1, wherein the .lambda.

6. The phase change material has a melting area ΔT as determined by DSC. ｆ Peak T ｆ As much as possible (T １ +T ２ ) / 2, and T １ is the hydrogen desorption temperature at the operating desorption pressure, and T 2 10. The composite material of claim 1, wherein: ##EQU1## is the hydrogen absorption temperature of the hydride at the operating desorption pressure.

7. 10. The composite material of claim 1, which is in the form of a compressed material.

8. 10. The composite material of claim 1 further incorporating a heat transfer enhancer.

9. 9. The composite material of claim 8, wherein the heat transfer enhancer is expanded natural graphite (ENG).

10. A hydrogen storage tank comprising the composite material of claim 1 connected to a fuel cell.

11. 10. A method for operating a hydrogen storage system based on a metal hydride capable of releasing and absorbing hydrogen, characterized in that the composite material of claim 1 is sequentially charged with hydrogen and then evacuated again.

12. The method of claim 11, wherein the hydrogen is discharged at a pressure of from 10 kPa to 2,000 kPa.

13. The method according to claim 12, wherein the hydrogen is charged at a pressure of 150 kPa to 70,000 kPa.

Images