Delivery of cold hydrogen in glass fiber composite pressure vessels

We are proposing to minimize hydrogen delivery cost through utilization of glass fiber tube trailers at 200 K and 70 MPa to produce a synergistic combination of container characteristics with properties of hydrogen gas: (1) hydrogen cooled to 200 K is ∼35% more compact for a small increase in theoretical storage energy (exergy); and (2) these cold temperatures (200 K) strengthen glass fibers by as much as 50%, expanding trailer capacity without the use of much more costly carbon fiber composite vessels.     

Modeling of sudden hydrogen expansion from cryogenic pressure vessel failure

We have modeled sudden hydrogen expansion from a cryogenic pressure vessel. This model considers real gas equations of state, single and two-phase flow, and the specific “vessel within vessel” geometry of cryogenic vessels. The model can solve sudden hydrogen expansion for initial pressures up to 1210 bar and for initial temperatures ranging from 27 to 400 K. For practical reasons, our study focuses on hydrogen release from 345 bar, with temperatures between 62 K and 300 K. The pressure vessel internal volume is 151 L. The results indicate that cryogenic pressure vessels may offer a safety advantage with respect to compressed hydrogen vessels because i) the vacuum jacket protects the pressure vessel from environmental damage, ii) hydrogen, when released, discharges first into an intermediate chamber before reaching the outside environment, and iii) working temperature is typically much lower and thus the hydrogen has less energy. Results indicate that key expansion parameters such as pressure, rate of energy release, and thrust are all considerably lower for a cryogenic vessel within vessel geometry as compared to ambient temperature compressed gas vessels. Future work will focus on taking advantage of these favorable conditions to attempt fail-safe cryogenic vessel designs that do not harm people or property even after catastrophic failure of the inner pressure vessel.     

Hydrogen storage technology options for fuel cell vehicles: Well-to-wheel costs, energy efficiencies, and greenhouse gas emissions

Five different hydrogen vehicle storage technologies are examined on a Well-to-Wheel basis by evaluating cost, energy efficiency, greenhouse gas (GHG) emissions, and performance. The storage systems are gaseous 350 bar hydrogen, gaseous 700 bar hydrogen, Cold Gas at 500 bar and 200 K, Cryo-Compressed Liquid Hydrogen (CcH2) at 275 bar and 30 K, and an experimental adsorbent material (MOF 177) -based storage system at 250 bar and 100 K. Each storage technology is examined with several hydrogen production options and a variety of possible hydrogen delivery methods. Other variables, including hydrogen vehicle market penetration, are also examined. The 350 bar approach is relatively cost-effective and energy-efficient, but its volumetric efficiency is too low for it to be a practical vehicle storage system for the long term. The MOF 177 system requires liquid hydrogen refueling, which adds considerable cost, energy use, and GHG emissions while having lower volumetric efficiency than the CcH2 system. The other three storage technologies represent a set of trade-offs relative to their attractiveness. Only the CcH2 system meets the critical Department of Energy (DOE) 2015 volumetric efficiency target, and none meet the DOE’s ultimate volumetric efficiency target. For these three systems to achieve a 480-km (300-mi) range, they would require a volume of at least 105-175 L in a mid-size FCV.     

Study of a GaN Schottky diode based hydrogen sensor with a hydrogen peroxide oxidation approach and platinum catalytic metal

A platinum (Pt) catalytic metal and a hydrogen peroxide oxidation approach are utilized to fabricate a hydrogen sensor based on a GaN Schottky diode. The presence of a gallium oxide dielectric layer between the Pt metal and the GaN surface can increase the adsorption sites for dissociated hydrogen species, thereby improving the related sensing ability towards hydrogen gas. Experimentally, under introduced 1% hydrogen/air gas, the studied device shows a high sensing response ratio of 1.03 × 10⁵ at 300 K. In addition, the lowest detecting level of 1 ppm hydrogen at 300 K is obtained. This device also exhibits good high-temperature durability (≥573 K) and a high sensing speed. The response (recovery) time constant at 300 K is only 74 (103) sec even under a very low hydrogen concentration of 1 ppm; these time constant values are much smaller than those of palladium metal-based sensors. Under the 1% hydrogen/air, the response (recovery) time constant at 300 K is drastically reduced to 15 (19) sec. Furthermore, in order to improve the feasibility of transmitting the sensing data, the concept of linear differentiation method is employed to eliminate redundant data. The simulation result shows that the average of the reduced ratios can achieve 77.88%. Therefore, this Schottky diode device not only shows promise to detect hydrogen gas, but also can be utilized effectively in the transmission of sensing data.     

Effect of Co loading on the hydrogen storage characteristics of hollow glass microspheres (HGMs)

The use of hydrogen as a fuel either direct combustion in an IC engine or for power generation in fuel cells continues to be a topic of significant interest. Developing and popularizing fuel cells for vehicular or other stationary applications depends upon the availability of safe and reliable hydrogen storage method. The greatest challenge as of now in this regard is the production of a light weight, nontoxic and easily transportable material which can store hydrogen. World-wide research is being conducted on developing newer materials for hydrogen storage. Hollow glass microspheres (HGMs) can be considered to be a potential hydrogen carrier which can store and deliver hydrogen for energy release applications. In this paper, we are reporting the preparation and characterization of cobalt loaded HGMs from amber glass powder for hydrogen storage applications. The feed glass powder with different percentage of cobalt loading was prepared by soaking and drying the feed glass powder in required amount of cobalt nitrate hexahydrate solution. Further, the dried feed glass powder was flame spheroidised to get cobalt loaded HGMs. Characterizations of all the HGMs samples were done using SEM, FTIR and XRD techniques. Hydrogen adsorptions on all the samples were done for 10 bar pressure at room temperature and 200 °C for 5 h. The results showed that the hydrogen adsorption capacity on these samples increased with increase in cobalt wt% from 0.2 to 2.0%. The hydrogen storage capacity of HACo2 was found to 2.32 wt% for 10 bar pressure at 200 °C.     

Sustainable H2 generation via steam reforming of biogas in membrane reactors: H2S effects on membrane performance and catalytic activity

This study proposes the steam reforming of a synthetic biogas stream containing 200 ppm of H₂S, carried out in a non-commercial supported Pd–Au/Al₂O₃ membrane reactor (7–8 μm selective layer thickness) at 823 K and 150 kPa over a non-commercial Rh(1%)/MgAl₂O₄/Al₂O₃ catalyst. This system is able to recover almost 80% of the total hydrogen produced during the reaction and shows good resistance to the H₂S contamination, as confirmed by stable methane conversions for more than 400 h under operation. For comparison, the same reaction was carried out in a commercial self-supported Pd–Ag membrane (150 μm wall thickness), yielding a hydrogen recovery equal to 40% at 623 K and 200 kPa, and presenting stable methane conversions for less than 200 h under operation due to the effect of the H₂S contamination.     

Structural strength analysis and optimization of portable hydrogen storage vessel made of fiberglass tube

Compared to steel, glass has higher strength and lower density, which makes it stand out as a pressure resistant vessel for hydrogen storage. However, glass easily breaks when it encounters locally concentrated stress. For high pressure hydrogen storage, the stress distribution of a glass vessel during pressure loading needs to be homogeneous without local stress concentration. Herein, the stress-strain behavior of portable hydrogen storage vessels made of glass fiber tubes is investigated theoretically and experimentally, respectively. The effects of different glass materials, wall thickness and pressure on the strength of the microtubes are investigated. Meanwhile, the method of filling the triangular gaps and adding solid fiberglass border was proposed to reduce the stress concentration. The result reveals that glass materials have little effect on the strength of microtubes. The optimal wall thickness is 12.5 μm for microtubes with an inner diameter of 100 μm. Filling the triangular gaps can reduce stress and expansion. The arrayed microtubes with solid fiberglass border are less deformed during fiber drawing technique. The stress increases at the tangent point of the arrayed microtubes with solid fiberglass border, but the stress of the outermost microtubes is significantly decreases.     

Hydrogen storage potential in MIL-101 at 200 K

Hydrogen adsorption isotherms for MIL-101 metal-organic framework are reported within a wide pressure range for temperatures between 77 and 295 K. Data modeling with the modified Dubinin-Astakhov equation shows a good fitting with the experimental results. The calculated absolute adsorption allowed the evaluation of the total hydrogen storage capacity for high pressure storage tank filled with MIL-101 as sorbent. The results show that the gravimetric and volumetric storage capacities at 198 K and 70 MPa are within the present-day accepted DOE targets, even if the storage capacity is slightly decreased by 3–6% as compared to the tank without sorbent. Moreover, the calculations reveal that the dormancy time is much increased, as compared to a tank without sorbent, exceeding the ultimate DOE target of 14 days. The MIL-101 assisted cold high-pressure hydrogen storage at ∼200 K and 70 MPa, brings about an additional advantage and seems promising for both mobile and stationary applications.     

One-step process of hydrogen storage in single walled carbon nanotubes-tin oxide nano composite

Hydrogen intake study on single walled carbon nanotubes (SWCNTs)-tin oxide (SnO₂) nano composite films have been performed. The composite is prepared on glass substrates in hydrogen atmosphere by electron beam evaporation (e-beam) technique. The process of hydrogenation has been done during the preparation of hydrogen storage medium itself, as one-step process. The amount of hydrogen incorporated in the composite is found to be 2.4 wt.%. The entire (100%) amount of stored hydrogen is released in the temperature range of 200–350 °C. The stored hydrogen has weak chemical binding in the SWCNTs-SnO₂ nano composite.     

Hydrogen storage thermodynamic and dynamic properties of as-milled CeMgNi-based CeMg12-type alloys

Ni was chosen to partially substitute the Mg of alloys to investigate the effect on hydrogen storage dynamics of NdMg₁₂-type alloy. The amorphous and nanocrystalline alloys were synthesized by mechanical milling technology based on CeMg₁₁Ni + x wt% Ni (x = 100, 200) alloys. This paper systematically narrates and investigates the influences of Ni content and milling duration on hydrogen storage performance. Sievert apparatus and differential scanning calorimetry (DSC) were utilized for investigating the de-/hydriding performances of samples. Both Arrhenius and Kissinger methods were utilized in this paper for estimating the dehydrogenation activation energy of hydrides, and found that enhancing Ni content can decrease the thermodynamic parameters (ΔH and ΔS) of alloys slightly and improve the dehydriding dynamics significantly. Furthermore, the hydrogen storage property can be affected significantly by adjusting milling time. With varying milling time, the hydrogen storage capacities can reach the maximum values of 5.691 and 5.904 wt% for x = 100 and 200 alloys separately. The hydrogen absorption saturation ratio (R^a(10)) at 573 K and 3 MPa also obtains maximum values with the variation of milling time, namely 90.17% and 99.32% for x = 100 and 200 alloys separately. The hydrogen desorption ratio (R^d(20)) always increases with milling time increasing. To be specific, prolonging milling time from 5 to 60 h results in the increase of R^d(20) at 593 K from 37.55% to 47.21% for x = 100 alloy and 47.29%–61.70% for x = 200 alloy.     

CFD simulation of heat transfer and phase change characteristics of the cryogenic liquid hydrogen tank under microgravity conditions

The heat transfer and phase change processes of cryogenic liquid hydrogen (LH₂) in the tank have an important influence on the working performance of the liquid hydrogen-liquid oxygen storage and supply system of rockets and spacecrafts. In this study, we use the RANS method coupled with Lee model and VOF (volume of fraction) method to solve Navier-stokes equations. The Lee model is adopted to describe the phase change process of liquid hydrogen, and the VOF method is utilized to calculate free surface by solving the advection equation of volume fraction. The model is used to simulate the heat transfer and phase change processes of the cryogenic liquid hydrogen in the storage tank with the different gravitational accelerations, initial temperature, and liquid fill ratios of liquid hydrogen. Numerical results indicate greater gravitational acceleration enhances buoyancy and convection, enhancing convective heat transfer and evaporation processes in the tank. When the acceleration of gravity increases from 10^?2 g0 to 10^?5 g0, gaseous hydrogen mass increases from 0.0157 kg to 0.0244 kg at 200s. With the increase of initial liquid hydrogen temperature, the heat required to raise the liquid hydrogen to saturation temperature decreases and causes more liquid hydrogen to evaporate and cools the gas hydrogen temperature. More cryogenic liquid hydrogen (i.e., larger the fill ratio) makes the average fluid temperature in the tank lower. A 12.5% reduction in the fill ratio resulted in a decrease in fluid temperature from 20.35 K to 20.15 K (a reduction of about 0.1%, at 200s).     

Reversible hydrogen storage in vapour deposited Mg-5 at.% Pd powder composites

Mg-5 at.% Pd powder composites derived from multilayered films of Mg and Pd deposited in Pd/Mg/Pd/Mg/Pd layer configuration by thermal evaporation reversibly store about 3.5 wt.% hydrogen up to 15 cycles under mild conditions of pressure and temperature. Hydrogenation takes place at 0.15 MPa hydrogen pressure while dehydrogenation occurs in a dynamic rotary vacuum. Each process is completed in about three hours. The temperature of a dehydrogenation or hydrogenation step is about 5–10 K higher than the preceding hydrogenation or dehydrogenation step. The hydrogenation temperature of the first cycle is 343 K whereas the dehydrogenation temperature of the 15th cycle is 423 K. The hydrogen storage capacity of composite is the manifestation of fine-grained microstructure of Mg and the catalytic properties of Pd. It declines beyond 423 K due to the exhaustion of metallic Pd as a result of the formation of Mg–Pd intermetallic compounds. This approach presents a simple and rapid method of preparing Mg–Pd composites for hydrogen storage applications.     

Doping engineering: Highly improving hydrogen evolution reaction performance of monolayer SnSe

By using the first-principles approach, we explore the hydrogen evolution reaction (HER) performance of SnSe monolayer. It is found that the SnSe monolayer with or without intrinsic defects is not good HER catalyst. By doping eighteen different elements at Sn or Se sites of the SnSe monolayer, we find that the elements P and In can effectively reduce the free energies of hydrogen (H) adsorption (ΔG) to −0.1 eV and 0.21 eV, much lower than 1.45 eV of perfect monolayer SnSe. This is attributed to great dispersion of electronic density of states of absorbed hydrogen atom having small interactions with doping elements. However, strong hybridizations between H and doping elements (K and Te) increase the ΔG values of doping systems (ΔG = 2.84 eV and ΔG = 1.77 eV).     

Hydrogen absorption/desorption behavior of Mg50La20Ni30 bulk metallic glass

In this work, Mg₅₀La₂₀Ni₃₀ bulk metallic glass (BMG) was prepared and its hydrogen absorption/desorption behavior was studied. The amorphous structure was found to be retained after gaseous hydrogenation. The T_g and T_x of the hydrogenated Mg₅₀La₂₀Ni₃₀ BMG was 561 K and 619 K respectively, much higher than the corresponding value of 463 K and 504 K of the unhydrogenated sample. Mg₅₀La₂₀Ni₃₀ BMG absorbed 0.73 and 1.85 wt% hydrogen within 1 h at 313 K and 423 K respectively, which was higher than that of ball-milled Mg₂Ni alloy. Mg₅₀La₂₀Ni₃₀ BMG exhibited an equilibrium hydrogen absorption plateau with a pressure of 0.07 MPa in pressure–composition isotherm curve at 423 K. It suggested that Mg-based BMGs are promising materials for hydrogen storage applications.     

Hydrogen absorption kinetics of magnesium fiber prepared by vapor deposition

The hydrogen absorption behavior of Mg fiber was observed over a temperature and pressure range of 560-620 K and 0.4-1.6 MPa, respectively. The Mg fiber had a diameter of 200 nm to 1 μm and consisted of grains smaller than 100 nm. The absorption kinetics was analyzed using the Arrhenius and Johnson-Mehl-Avrami-Kolmogorov equations. Obtained kinetics parameters for the Mg fiber were compared with those of conventional Mg powder with the particle size of tens of micrometers. The initial reaction rate of the Mg fiber was larger than that of Mg powder. The absorption behavior was well-described by the nucleation and growth model. The values of Avrami exponent for the initial absorption varied from 0.8 to 2.5; these values are larger than those obtained for Mg powder (0.6-1.3). The Avrami exponents varied wider at higher temperatures, and increased with decrease in pressure. The obtained values of Avrami exponent for both the Mg fiber and the powder corresponded to a reaction through the rate-limiting step of hydrogen diffusion in Mg. The activation energies were estimated to be 69 kJmol⁻¹-H₂ for the powder Mg and 72 kJmol⁻¹-H₂ for the Mg fiber, respectively. The pre-exponential factor in the Arrhenius equation for the Mg fiber was approximately three times larger than that for the Mg powder.     

Investigation of cryo-adsorption hydrogen storage capacity of rapidly synthesized MOF-5 by mechanochemical method

Comparisons were made between the samples mechanochemically (MOF-5(M)) and solvothermally (MOF-5(S)) prepared for the development of efficient hydrogen storage medium. Synthesized samples were undergone structural characterization as well as adsorption equilibrium measurements of hydrogen at temperature-pressure range 77 K–87 K and 0.1–10 MPa. Grand Canonical Monte Carlo (GCMC) simulations were further conducted to study the behaviors of hydrogen molecules adsorbed on MOF-5. It shows that, besides the advantage of large scale synthesis and a lower cost, mechanochemical method respectively brings about 207% and 90.5% increments in the specific surface area and the maximum excess adsorption capacity of hydrogen at 77 K within pressure range 0–10 MPa. Results also reveal that the crystal within MOF-5(M) is regular and distributing uniformly with a mean size only one tenth of that of the MOF-5(S); at 77 K within pressure range 0–10 MPa, Toth equation can predict the adsorption equilibrium data of hydrogen on two MOF-5 samples with a mean relative error less than 1.5%. It suggests that MOF-5(M) is more promising for hydrogen storage by adsorption for practical applications.     

Topological defects embedded large-sized single-walled carbon nanotubes for hydrogen storage: A molecular dynamics study

In this paper, we investigate the performance of large-sized single-walled carbon nanotubes (SWCNTs) incorporated with mono vacancy (MV), double vacancy (DV), and Stone-Wales (SW) topological defects as a medium for hydrogen adsorption using molecular dynamics (MD) simulations. A novel potential energy distribution (PED) method is employed with MD simulations to determine the adsorbed hydrogen molecules and associated binding energy. In addition, we extended our work to bundles of defected SWCNT (D-SWCNT) that provided the most prominent adsorption capacity subjected to temperature and pressure variations. In particular, four representative (8,8), (13,13), (19,19), and (33,0) SWCNTs are simulated under various thermodynamic conditions, and collected adsorption isotherms data reveals higher gravimetric density for large-sized SWCNT. At 77 K and 100 bar, the maximum hydrogen uptake in pristine SWCNTs is 6.88–7.73 wt%, depending on the size of the nanotubes. In contrast, the binding energy decreases as the nanotube size increases. At 77 K, (8,8) and (19,19) SWCNTs have average binding energies of 0.043 and 0.021 eV, respectively. Meanwhile, (19,19) SWCNT incorporated with 1% DV defects having 5–8 rings (DV1) and MV defects yields the maximum storage capacity of 9.07 wt% and 8.62 wt%, respectively, at 77 K. Furthermore, the increment of about 43.29% in wt.% is obtained for DV1 defected nanotube relative to pristine SWCNT at 300 K and 100 bar. Moreover, our results indicate the maximum hydrogen uptake of 8.65, 7.15, 2.57, and 1.33 wt% in the square array of DV1 defect embedded SWCNTs at 77, 100, 200, and 300 K, respectively, compared to 9.07, 6.65, 2.24, and 1.11 wt% in the isolated D-SWCNT at identical conditions. As a result, the D-SWCNT bundles are better suited for hydrogen storage at high temperatures than the isolated D-SWCNT. Our present study paves the way to progress toward the efficient usage of D-SWCNTs with few chemical alterations for scaled-up applications.     

“Preliminary results of hydrogen production from water vapor decomposition using DBD plasma in a PMCR reactor”

The water decomposition is considered one of the most attractive chemical processes for the production of hydrogen. The present work describes the preliminary results obtained in the experimental study of the water vapor dissociation into hydrogen and oxygen species using Dielectric-Barrier Discharge (DBD) plasma in a plate micro-channel reactor (PMCR). The water vapor molecules are injected without using carrier gas into the PMCR reactor at pressure of 100 kPa and temperature of 573 K. The applied high voltage of the plasma was within range of 14–18 kV and different steam flow rates have been analyzed within range of 100–200 ml/h. The product gases have been separated in ice trap which it was connected directly to the PMCR reactor to prevent the recombination of hydrogen and oxygen species. The concentration of the outlet species has been measured in a gas phase chromatography (GC) instrument. The PMCR reactor heating temperature effect on the water vapor decomposition has been analyzed. It was found that the water vapor is dissociated into their constituent molecular elements of hydrogen and oxygen gas using plasma. The maximum obtained mole fraction, hydrogen flow rate and conversion rate were 2.3%, 9.42 g/h, 42.51% respectively, at steam temperature of 573 K, pressure 100 kPa, PMCR heating temperature 403 K, steam flow rate of 200 ml/h and the plasma discharge high voltage of 18 kV. It was observed that the amount of evolved hydrogen concentration increased with the increase of the PMCR reactor heating temperature. Also, the thermal efficiencies versus the heat supplied have been calculated and the maximum obtained efficiency was 49.32%. Consequently, the evolved hydrogen flow rate appears to depend mainly on the plasma voltage, PMCR reactor heating temperature and the separating temperature of outlet hydrogen and oxygen species. The steam dissociation experiment will be extended to separate hydrogen and oxygen species elements at high temperature conditions.     

Lithium decoration characteristics for hydrogen storage enhancement in novel periodic porous graphene frameworks

Hydrogen storage in porous materials by physical adsorption is being discussed to provide widespread usage of hydrogen energy systems. One of the recent hydrogen storage media that store hydrogen physically is Porous Graphene Frameworks (PGFs). In the study, three different PGFs were constructed by using Benzene-1,3,5-tricarboxylic acid (BTC), 4,40,400-Benzene-1,3,5-triyltribenzoate (BTB) and 4,40,400-(benzene-1,3,5triyl-tris (benzene-4,1-diyl))tribenzoate (BBC) organic linkers. The geometries of the structures were optimized and lithium atoms were dispersed inside. Then, thirty-three different structures were derived. Finally, hydrogen storage capacities and surface areas of each structure were computed. It was found out that 160 lithium dispersed Graphene-BBC structure has the highest hydrogen storage capacity with 4.26 wt % at 298K and 100 bars while 70 lithium dispersed graphene-BTB structure store 9.81 wt % hydrogen at 77K and 4 bars, and lithium free graphene-BBC structure store 20,68 wt % hydrogen at 77K and 100 bars. Lithium dispersion enabled extra surfaces for Graphene-BTB and Graphene-BBC structures to the limits. But surface area of Graphene-BTC structure decreased with lithium dispersion. The number of limits for Graphene-BTB and Graphene-BBC named structures were 70 and 200 lithium atoms, respectively. At the final it is pointed out that constructed novel PGFs could store comparable and relatively high hydrogen in various conditions. The existence of lithium atoms played a minor role to enhance hydrogen storage capacity but the limits are critically important to reach maximum capacity.     

Magnesium and iron loaded hollow glass microspheres (HGMs) for hydrogen storage

The development of a safe and efficient method for hydrogen storage is essential for the use of hydrogen with fuel cells for vehicular applications. Hollow glass microspheres (HGMs) have characteristics suitable for hydrogen storage and are expected to be a potential hydrogen carrier to be used for energy release applications. The HGMs with 10–100 μm diameters, 100–1000 Å pore width and 3–8 μm wall thicknesses are expected to be useful for hydrogen storage. In our research we have prepared HGMs from amber glass powder of particle size 63–75 μm using flame spheroidisation method. The HGMs samples with magnesium and iron loading were also prepared to improve the heat transfer property and thereby increase the hydrogen storage capacity of the product. The feed glass powder was impregnated with calculated amount of magnesium nitrate hexahydrate salt solution to get 0.2–3.0 wt% Mg loading on HGMs. Required amount of ferrous chloride tetrahydrate solution was mixed thoroughly with the glass feed powder to prepare 0.2–2 wt% Fe loaded HGMs. Characterizations of all the HGMs samples were done using FEG-SEM, ESEM and FTIR techniques. Adsorption of hydrogen on all the Fe and Mg loaded HGMs at 10 bar pressure was conducted at room temperature and at 200 °C, for 5 h. The hydrogen adsorption capacity of Fe loaded sample was about 0.56 and 0.21 weight percent for Fe loading 0.5 and 2.0 weight percentage respectively. The magnesium loaded samples showed an increase of hydrogen adsorption from 1.23 to 2.0 weight percentage when the magnesium loading percentage was increased from 0 to 2.0. When the magnesium loading on HGMs was increased beyond 2%, formation of nano-crystals of MgO and Mg was seen on the HGMs leading to pore closure and thereby reduction in hydrogen storage capacity.