Hydrogen Capacity Research Articles

Crystal structure of deuteride phase of Nd-Ni alloy by X-ray and neutron diffraction

The hydrogen-absorbing alloys currently used in industry form residual hydrogen that reduces the alloy’s reversible hydrogen capacity, decreasing its useful life. RNi3 intermetallic compounds, which have a PuNi3-type crystal structure composed of MgZn2-type and CaCu5-type cells that exhibit structural change in relation to their hydrogenation properties, have been the focus of much research, but only a few of those reports focus on the interplay between residual hydrogen and alloy structure. Thus, this study seeks to clarify the residual hydrogen occupation mechanisms in MgZn2-type and CaCu5-type cells during the hydrogen absorption-desorption process. The structural changes and deuterium occupation in NdNi3Dx were investigated using X-ray diffraction (XRD) and neutron powder diffraction (NPD). Rietveld refinement was performed for NdNi3, NdNi3D2.6, NdNi3D3.2, NdNi3D4.0, and NdNi3D4.8, during the deuterium absorption-desorption process. The deuterium capacity reached 0.9 D/M at the first absorption process and 0.7 D/M of residual deuterium was formed after the first desorption at 248 K. For NdNi3D2.6 (phase II), the residual deuterium contents of MgZn2-type and CaCu5-type cells were determined to be 1.0 D/M and 0.4 D/M, respectively. The residual deuterium preferred the deuterium site in the MgZn2-type cell. The deuterium capacity was 1.2 D/M in the first absorption process at 213 K and the residual deuterium was 1.0 D/M at the end of the first desorption. The severe peak broadening observed in the XRD and neutron diffraction patterns of NdNi3D4.0 and NdNi3D4.8 indicate that the deformation of the metal sublattice of the deuteride phase was deformed over 0.8 D/M.

Lightweight alkali-induced lattice-dynamical stability and energy storage mechanism of quaternary Mg-based hydrides under pressure effect

New-discovery compositions of the lightweight quaternary Mg-based hydrides at ambient pressure are found as NaLiMgH4, NaLiMg2H6, and Na3LiMg4H12, which their stabilities were determined by all positive modes of the phonon dispersion relation. The varying compositions of Na-Li-Mg-H were analyzed using the ab initio random structure searching technique and affirmed by mechanical stability and Born stability criteria. Besides, the effects of pressure on stable structures are considered also. High-gravimetric hydrogen capacity introduces us to study H-vacancy occurrence and H-diffusion kinetics in these lightweight quaternary hydrides. Our calculation results indicated that the NaLiMg2H6 in the P21/m system gave more suitable for hydrogen storage material due to lower energy barriers as well as the hydrogen diffusion kinetics in this lightweight hydride for its practical use in energy storage applications.

In situ formed Mg(BH4)2 for improving hydrolysis properties of MgH2

The hydrolysis of MgH2 delivers high hydrogen capacity (15.2 wt%), which is very attractive for real-time hydrogen supply. However, the formation of a surface passivation Mg(OH)2 layer and the large excess of H2O required to ensure complete hydrolysis are two key challenges for the MgH2 hydrolysis systems. Now, a low-cost method is reported to synthesize MgH2@Mg(BH4)2 composite via ball-milling MgH2 with cheap and widely available B2O3 (or B(OH)3). By adding small amounts of B2O3, the in-situ formed Mg(BH4)2 could significantly promote the hydrolysis of MgH2. In particular, the MgH2–10 wt% B2O3 composite releases 1330.7 mL·g−1 H2 (close to 80% theoretical hydrogen generation H2) in H2O and 1520.4 mL·g−1 H2 (about 95%) in 0.5 M MgCl2 in 60 min at 26 °C with hydrolysis rate of 736.9 mL·g−1·min−1 and 960.9 mL·g−1·min−1 H2 during the first minute of the hydrolysis, respectively. In addition, the MgCl2 solution allows repeated use by filtering and exhibits high cycle stability (20 cycles), therefore leading to much reduced capacity loss caused by the excess H2O. We show that by introducing B2O3 and recycling the 0.5 M MgCl2 solution, the system hydrogen capacity can approach 5.9 wt%, providing a promising hydrogen generation scheme to supply hydrogen to the fuel cells.

Photohydrolysis of Ammonia Borane for Effective H2 Evolution via Hot Electron-Assisted Energy Cascade of Au-WO2.72/TiO2

Catalytic hydrolysis of ammonia borane has drawn much attention for on-board hydrogen generation because of its high hydrogen capacity. Herein, a ternary Au-WO2.72/TiO2 hybrid is synthesized for efficient photohydrolysis of ammonia borane. The Au nanoparticles (NPs) deposited were in situ-reduced by defective WO2.72 nanowires, and 2 wt % Au-WO2.72 is optimal to realize high photoactivity because of the high light absorption and low charge-transfer resistance, which is then combined with TiO2 nanosheets to form a 2%Au-WO2.72/TiO2 hybrid. This hybrid possesses compact interfaces among Au, WO2.72, and TiO2, and the electron pump effect of Au surface plasmon resonances and the electron capture property of TiO2 accelerate the electron transfer from WO2.72 to Au and then to TiO2, leading to the effective separation and long lifetime of photoinduced charges. Therefore, the 2%Au-WO2.72/TiO2 hybrid shows very high catalytic activity under visible light with H2 evolution rates 2.67- and 31-times higher than those for 2%Au-WO2.72 and WO2.72, respectively.

Trapping Hydrogen Atoms in Vacancies of Li2TiO3 Crystal: A First-Principles Study.

The hydrogen atom capacity in the vacancies of the Li2TiO3 crystal is systematically studied by the first-principles method to evaluate its tritium release performance as a solid breeder material in nuclear fusion reactors. The adsorption process of adding hydrogen atoms one by one in the vacancy are investigated to find the possible adsorption sites of the hydrogen atoms in the vacancy. The charge transfer and density of states analysis are performed to reveal the form of a hydrogen–hydrogen dimer in the vacancy. Also, the trapping energy and formation energy are defined and calculated to determine the hydrogen atom capacity of the system. According to the simulations, the Ti vacancies have the strongest hydrogen atom capacity followed by Li vacancies, and O vacancies are the weakest. The influence of hydrostatic pressure on the hydrogen atom capacity is also investigated. Our results reveal the hydrogen capacity of vacancies in the Li2TiO3 crystal from the atomic scale, which also provide a theoretical guide to the related tritium release experiments.

Hydrogen dissociation in Li-decorated borophene and borophene hydride: An ab-initio study

Lithium (Li) dopants have garnered attention as a means to enhance hydrogen (H2) binding energies and capacities in 2D boron-based materials. However, it is unclear if and how these dopants affect H2 dissociation and chemisorption. Using density functional theory (DFT) and nudged elastic band (NEB) calculations, reaction pathways for H2 dissociation on borophene-hydride and striped-borophene are investigated in the presence of Li dopants. Our results indicate that tuning the Li-loading can increase the reversibility and the rate of dehydrogenation for both borophene-hydride and striped borophene. In particular, for Li-doped borophene-hydride, the heat of reaction for H2 release is reduced by more than 85% compared to the pristine structure (1.97 eV/H2). Our results signify that Li-doping can considerably change the H2 chemisorption properties of striped-borophene and borophene-hydride, and can lead to promising materials for H2 storage.

Methods to Improve the First Hydrogenation of the Vanadium-Rich BCC Alloy Ti16V60Cr24

In this paper we report the effect of three different preparation methods on the first hydrogenation of the vanadium-rich BCC alloy Ti16V60Cr24: one-time cold rolling, 5 min ball milling and addition of 4 wt.% of Zr. All samples were synthesized by arc melting. Without Zr addition the alloy was single phase, but when 4 wt.% Zr was added, a secondary zirconium-rich phase was present. However, X-ray diffraction patterns only showed a single-body-centred cubic phase before hydrogenation for all samples. The crystal structure of the fully hydrogenated samples was body-centred tetragonal. The highest hydrogen capacity (3.8 wt.%) was measured for the Zr-doped alloy. The ball-milled alloy also exhibited a high storage capacity and fast kinetics. However, the maximum hydrogen storage capacity slightly decreased after cold rolling. It was found that air exposure increases incubation time for the first hydrogenation. The incubation time was shortened by cold rolling which, however, reduced the hydrogen storage capacity. The Pressure-Composition isotherms of Ti16V60Cr24 + 4 wt.% Zr at 297, 303 and 323 K were determined. The determined enthalpy and entropy of hydrides formation were −41 ± 5 kJ/mol and −134 ± 14 J/mol/K, respectively.

Capture‐Transport Double Enhancement Strategy to Construct High‐efficiency Photo‐catalysts with p‐n Junction for Hydrogen Production under Visible‐light Irradiation

AbstractThe conversion of solar energy into chemical energy by photo‐hydrolysis is considered as an effective way to solve current energy and environmental problems. The preparation of photo‐catalysts with excellent activity is expected to promote the rapid development of photo‐catalytic hydrogen production research. A two‐step strategy is used to obtain a CdS‐based photo‐catalyst with enhanced photo‐hydrogen production efficiency by improving the electron transport efficiency and the intrinsic electric field to promote electron separation. The CdS/Ag2S/NiS nanocomposites were prepared by a two‐step method in this work. After characterization of the structure, optical properties and surface chemical state by XRD, EDS, XPS, TEM and UV‐vis, it is found that Under visible light exposure (λ=420 nm), when the ratio of NiS is 11 %, the sample got the highest hydrogen yield (3280 μmol ⋅ g−1 ⋅ h−1), which is 2.8 times of CdS/Ag2S material, and also showing good cycle stability. The improved catalytic efficiency can be attributed to two points: the introduction of Ag2S provides more electro‐chemical active sites and routes for nano‐materials; the introduction of NiS builds an internal electric field to promote the transmission and separation of optical electrons and holes, and improve aquatic hydrogen capacity.

Enhanced hydrogen adsorption in alkali metal based copper hexacyanoferrate Prussian blue analogue nanocubes

Two Prussian blue analogues (PBAs) CuII[FeIII(CN)6)]2/3·15H2O (1), and KICuII[FeII(CN)6)]3/4·9H2O (2) are synthesised using a co-precipitation method at room temperature. The compounds are studied using XRD (x–ray diffraction), FESEM (Field Emission Scanning Electron Microscopy), IR (infrared), Raman spectroscopy, and TGA (thermogravimetric analysis). The surface morphology of the compounds is investigated using the FESEM technique, which confirms the formation of cube-type microstructure with an average size of ∼200 and ∼120 nm for compounds (1), and (2), respectively. The x-ray diffraction (XRD) results, derived from the Rietveld refinement method, reveal that both the compound crystallized in a pure single nanocrystalline phase with face centred cubic crystal structure of space group Fm3m. The lattice constants are found to be ∼10.04, and ∼10.08 Å for the compound (1), and (2) respectively. The IR and Raman spectroscopy show characteristic peaks, observed in the range of 1900–2200 cm−1, corresponds to the CN stretching frequency of CuII–CN–FeIII/II, confirming the formation of PBAs compounds. The hydrogen adsorption isotherm measurements have been used to investigate the molecular hydrogen adsorption into PBAs compounds at low temperature (77 K) conditions. The compounds (1) and (2) show hydrogen storage capacity of ∼1.12 and 1.63 wt %, respectively. The compound (2) shows an enhanced hydrogen capacity of ∼45% as compared to compound (1), which is due to the presence of unsaturated Cu/Fe metal ions, and the larger surface area of the nanocubes in the framework structure. In addition, the presence of K+ ions in the compound (2) also strongly favours to catalysing more H2 for their enhanced storage capacity.

Charge and Hydrogen Storage Capacities of Electrodeposited Graphene Derivatives

Graphene’s theoretical capacitance and physical hydrogen storage abilitiesmark it as one of the best candidates for energy storage application. Graphene oxide (GO) is easy to manufacture in bulk synthesis and can be considered as a precursor for graphene synthesis. The application of graphene on the surface of electrodes can be achieved by different techniques as drop-coating and electrodeposition. It has been reported that the electrochemical hydrogen storage is favored in samples with a well-developed porosity and a low content in surface oxygen complexes. Both features indicate that the unsaturated carbon atoms in the carbon materials have an important role for the hydrogen uptake. It has also been suggested that the total capacity of hydrogen storage is proportional to the interlayer distance and not to the carbon specific surface area.The present work presents an investigation of electrodeposited GO coatings (ED), which have subsequently been electroreduced to various degrees of rGO, and relate their charge capacitance and hydrogen storage capacity to the preparation mode, morphological structure, and surface chemistry. These properties were compared to those of drop-cast (DC) coatings of GO.The ED coatings were characterized by more accumulated graphene sheets imperfections as observed by cross section TEM analysis. These coatings, when reduced at -1.6 V vs Hg/HgO showed more efficient removal of phenolic groups than DC ones treated at the same potential (remaining contents of 2.1 and 18.1 %, respectively). They also showed lower charge transfer resistance (5.2 and 28 Ω cm2, respectively), higher capacitance (73.2 and 42.6 F/g, respectively), and higher hydrogen storage capacity (119 and 57 mAh/g, respectively). Moreover, they showed higher stability towards H2 charge/discharge cycles (retained hydrogen capacities of 95 and 40 % after 15 and 6 cycles for ED and DC coatings reduced at -1.5 V, respectively).The removal during the electroreduction process of phenolic groups located at the graphene sheets edges of the ED coatings and their higher pseudo-capacitance can explain their lower charge transfer resistance and their higher pseudo-capacitance, respectively. Their superior stability towards hydrogen charge/discharge cycles is suggested to stem from evolving hydrogen escape routes created during the ED process. The superior performance properties of coatings obtained by ED and subsequently electro-reduced make them promising electrode materials for energy storage.

Design of LPSO-introduced Mg96Y2Zn2 alloy and its improved hydrogen storage properties catalyzed by in-situ formed YH2

The long period stacking ordered (LPSO) structure in Mg-based alloy presents a high content of Mg and evenly-dispersed transition metal (TM) and rare earth (RE) elements, which shows great potential in hydrogen storage. In this work, Mg96Y2Zn2 alloy with high proportion of LPSO structure was prepared, forming fine α-Mg dendrite and the interdendrite region with homogeneous Zn and Y distributions. Results indicate that Mg96Y2Zn2 alloy decomposes into YH2 + Mg(Zn) composite after hydrogen ab/desorption, of which nanosized YH2 is in-situ formed from the irreversible decomposition of LPSO and eutectic phase and Mg(Zn) is generated from the dissolution of Zn atoms in Mg lattice. This composite can absorb 5.36–5.79 wt% hydrogen and desorb hydrogen at a lower temperature than pure MgH2, which ascribes to the “hydrogen pump” effect of YH3 and the catalyst of MgZn2. The hydrogenation process of Mg96Y2Zn2 alloy is dominated by one-dimension diffusion rate of hydrogen atoms, while the dehydrogenation process is dominated by two-dimension interface movement of the metal/hydride phases. The in-situ formed YH2 nanophase and Mg(Zn) originated from LPSO structure are stable and evenly dispersed, thus the Mg96Y2Zn2 alloy shows enhanced hydrogenation capacity and kinetics.

Formation of AlNi phase and its influence on hydrogen absorption kinetics of Mg77Ni23-xAlx alloys at intermediate temperatures

In order to reduce the obstacle influence of coarse Mg2Ni phase on hydrogen absorption kinetics in Mg–Ni alloys, aluminum was doped and Mg77Ni23-xAlx (x = 0, 3, 6, 9) alloys were prepared. The results show that AlNi phase was formed when Al was added, the size of primary Mg2Ni phase decreases with increasing Al content till 6 at.%, while primary Mg2Ni phase was diminished and primary Mg phase was formed when Al content increased to 9 at.%. The initial hydrogenation rates of Mg77Ni23-xAlx alloys were increased, which is resulted from the refined primary Mg2Ni and the catalytic AlNi phase. More importantly, the hydrogenation rates and capacities were significantly improved at 150 °C, especially for the Mg77Ni17Al6 alloy. The apparent activation energy of the Mg77Ni17Al6 alloy for hydrogenation was reduced to 73.68 kJ/mol from 102.27 kJ/mol of the Mg77Ni23 alloy. Its enthalpy changes for hydrogenation at low and high platforms are 72.3 kJ/mol and 53.9 kJ/mol, respectively. The multiple channels and short distance for hydrogen atoms diffusion provided by refined primary Mg2Ni phase, the solid dissolution of Al in Mg2Ni lattice, and catalytic effect of AlNi on hydrogenation, leading to the improvement of the hydrogen storage properties.

Simulation methodology for hydrogen liquefaction process design considering hydrogen characteristics

One promising method to improve the storage capacity of hydrogen is to liquefy it, resulting in high energy density. However, liquefying hydrogen is a challenging task because hydrogen characteristics, such as a boiling point at a cryogenic temperature and changes in equilibrium compositions of spin isomers constituting hydrogen molecules, must be considered. For a design of a hydrogen liquefaction process, it is necessary to use an equation of state that can accurately calculate the properties of hydrogen, and to consider conversion reactions of the spin isomers. In this study, it is confirmed that the modified Benedict-Webb-Rubin equation is a suitable equation of state for simulating hydrogen liquefaction processes and that an equivalent model used in this study for the conversion reactions of the spin isomers shows reasonable results. Furthermore, the economic feasibility of the designed hydrogen liquefaction process is investigated based on energy optimization and economic analysis.

Understanding crystal structure roles towards developing high-performance V-free BCC hydrogen storage alloys

Current bottlenecks in the supply and high cost of V have negatively impacted their application. There is great interest in developing V-based hydrogen storage alloys that use less or free V. Here, we investigate the role of V in deliberately designed V-based alloys. Our results affirm that V plays an undeniable role in enhancing hydrogen storage properties. It is found that V maintains the stable single BCC structure but leads to more residual hydrogen (1.4 wt%) because of the high stability of the dihydride and smaller hydriding rate because of the small lattice parameter, which offers unexpected but encouraging perspectives towards reducing the need of V in such alloys. Mo substitution for V effectively alleviates the higher residual hydrogen to achieve a high dehydriding capacity of 2.5 wt%. Moreover, the suction-cast (Ti0.46Cr0.54)97.5Mo2.5 alloy, which keeps BCC structure after suction-cast process and contains a low-Mo content, also exhibits dehydriding capacity of 2.3 wt%. The enthalpy change as well as dehydriding capacity of V-Free alloys obtained were similar to those reported V-based alloys. These findings are attractive for developing new V-free BCC hydrogen storage alloys and higher hydrogen capacity.

Microwave Plasma Enhancing Mg-Based Hydrogen Storage: Thermodynamics Evaluation and Economic Analysis of Coupling SOFC for Heat and Power Generation

Hydrogen, as a kind of green and efficient energy, plays an increasingly important role in current social development. Hydrogen storage technology is considered to be one of the main bottlenecks in limiting the large-scale application of hydrogen energy. The solid-state hydrogen storage technology based on Mg-based materials has received extensive attention due to its advantages of high hydrogen capacity, good reversibility, and low cost, but there are still shortcomings such as high reaction temperature, large energy consumption, and slow reaction kinetics. In order to solve these problems, this article proposes a new method of using microwave plasma to ionize hydrogen into H− ion. The possible activation mechanism of microwave plasma to improve the hydrogen storage properties is put forward. Based on the activation mechanism, the thermodynamic performance of Mg-based hydrogen storage is evaluated using density functional theory. It is concluded that the reaction temperature is significantly reduced from 339°C to 109°C with the help of microwave plasma. In addition, the comparison between the conventional heating hydrogen storage process based on MgH2 and microwave enhanced advanced hydrogen storage process based on MgH2 systems coupled with solid oxide fuel cells for heat and power generation is conducted to evaluate the economic feasibility. The results show that the energy consumption cost of the proposed microwave plasma enhancing hydrogen storage system is approximately 1.71 $/kgH2, which is about 50% of the energy consumption cost of the conventional system.

First principles investigation on the hydrogen adsorption on planar aluminene with boron, carbon, and nitrogen as impurities

Materials including two-dimensional systems have been widely investigated for potential hydrogen storage. In this work, hydrogen adsorption on planar hexagonal aluminene with boron, carbon, and nitrogen decorations was studied using density functional theory. Results showed that boron, carbon, and nitrogen atom can be chemisorped without barriers on aluminene sites: top, hollow, and bridge. Density of states (DOS) showed that these systems remained metallic and nonmagnetic except for adatoms on top site of aluminene but its ferromagnetism are passivated once hydrogen atoms are adsorbed. The p orbitals of the adatoms and aluminium atoms formed the chemical bonding as shown by the DOS and supported by the charge density difference. Potential energy barriers were found in hydrogen adsorption on all systems indicating additional energy is needed to adsorb hydrogen on all systems. Hydrogen is chemisorped on surfaces where adatoms are at the top and bridge site through its s orbital and p orbital of the adatom, while H2 is physisorped for adatoms on the hollow site. The presence of boron, carbon, and nitrogen atoms on aluminene can reduce the hydrogen capacity of pristine aluminene due to the potential energy barriers.

Concurrent 2. Presentation for: Naturally derived carbon material for hydrogen storage

Presented on Tuesday 17 May: Session 2 Over the last few decades, hydrogen storage has become a vital issue for hydrogen technologies. Several techniques, such as adsorbents, hydrides, nanomaterials, metal–organic frameworks and porous polymers, have been widely explored for hydrogen storage. Although some techniques are promising, there are still challenges, such as operating temperature and pressure, cyclic reversibility and higher hydrogen content. The concept of carbon-based nanomaterials in hydrogen storage, among all the systems that are up-and-coming, appears to be promising, especially the carbon nanotubes (CNTs), activated carbons, and carbon particle systems. This work reports on the development of carbon material from naturally available biomass, such as waste date leafs, through the pyrolysis method and its hydrogen capacity and comparison with commercial CNTs. The synthesised carbon nanomaterial was characterised using field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and the Brunauer–Emmett–Teller method. The date leaf carbon nanomaterial was found to have better surface area and pore‐size distribution than CNTs, which is promising for hydrogen storage. To access the presentation click the link on the right. To read the full paper click here

Natural sources and conditions of geological hydrogen generation (in the context of hydrogen depositssearches)

World energy problems can largely be solved in the event of discovering huge amounts of gaseous hydrogen in a free state, which is considered as a promising alternative to the reserves of traditional fossil fuel in the earth’s crust. However, the hydrogen industry’s development is inhibited by many challenges, in particular, in geology. Today there is neither strategy for exploration activity nor resource evaluation due to the lack of relevant experience and practical recommendations aimed at geological hydrogen. The purpose of the work is to establish and analyze potential ways and geological conditions for the formation, migration, and accumulation of hydrogen of natural origin in the earth’s crust for the further justification of the concept of the search of free hydrogen accumulation. The author has considered all possible theoretical natural sources and ways of generating hydrogen naturally. Its origin is generally assumed to magmatic, thermogenic, endogenous, biogenic, as well as one that is caused by radiolysis, decomposition of organic matter, the interaction of water with reducing agents in the mantle. All known possible ways of the genesis of free hydrogen in natural conditions are analyzed. Geologically controlled sources of natural hydrogen can be grouped according to the main processes: aqueous processes of hydrolysis (several processes including the oxidation of iron minerals, radiolysis, cataclasis and metamorphism; decomposition of organic matter (including thermal maturing); decomposition of hydrogen-containing compounds (in particular, methane and/or ammonia at metamorphisms); deep degassing of Earth’s interior. Potential location areas of free hydrogen in a geological environment are analyzed. Natural conditions for high/increased hydrogen content have basins with the presence of hydrocarbons, recent deposits with prolific organic, coal beds, zones of tectonic faults, extrusive magmatic bodies, alkaline magmatic complexes, geothermal fields, crystalline basements, geologic formation of rocks enriched with potassium, salt-bearing sections and ultrabasic rocks. Due to the uncertainty concerning the ways and conditions for generating hydrogen in the earth’s crust, geological searches and possible further study of hydrogen accumulations require a mix of methods and approaches used for traditional searches of hydrocarbon deposits – conventional oil and gas fields (source rocks, basin, cap) given the features of free hydrogen, in particular, mobility and reactive capacity of its molecule. Regardless of the genesis of hydrogen, the main search criteria should be focused on the ways of its migration and the availability of a basin and a cap. This approach maximally combines hypotheses competing among themselves (from the viewpoint of the genesis of hydrogen). It is required the geological structure with the corresponding basin and fluid trap (cap), which, unlike the fluid traps in the usual sense, should be not only impermeable but also chemically neutral in relation to hydrogen.

Dehydrogenation performance of metal hydride container utilising MgH2-based composite

Mg-based hydrides have gained formidable interest for hydrogen storage applications due to their high intrinsic hydrogen capacity up to 7.6 wt%. However, their ability to absorb/desorb hydrogen is limited by their slow inherent kinetics and the heat and mass transfer within the storage container. The dehydrogenation of the metal hydride material in the container becomes important when coupling with a fuel cell, since the fuel cell requires a constant H2 flow rate to provide constant power output. In this study, we investigate numerically the dehydrogenation performance of a cylindrical container filled with 300 g of ball milled Mg90Ti10 + 5 wt% C with the objective to identify the operating conditions at which the H2 flow rate is higher or equal to the threshold for a proper functioning of a fuel cell. The heat exchange in the container is improved by a combination of internal basin-like and external annular fins. The heat transfer characteristics used in the numerical model are determined from the experimental work conducted in our laboratory. The results show that during the dehydrogenation process, at low convective heat transfer coefficient of 5–35 W/m2 K, the hydride container can supply H2 to a fuel cell with different power rating from 100 to 250 W for a long period of time with nearly constant flow rate.

A suitable design of metal hydride cartridge for a fuel cell assisted bicycle in consideration of heat transfer performance

Metal hydrides (MHs) can store hydrogen produced from biomass at low pressure and high volumetric energy density. However, the endothermic reaction that occurs during hydrogen discharge decreases the hydrogen flow rate, which prevents the generation of sufficient power for fuel cell (FC) devices. Because a previous study reported that the hydrogen capacity of MHs would drop by approximately 20% due to the hydrogen sulfide contained in hydrogen from biomass, the utilizable amount of hydrogen in MHs should be enhanced. In this study, MH utilization for an FC-assisted bicycle in consideration of waste heat recovery from MH to FC was investigated. The results show that the MH-based hydrogen storage system can weigh 8 kg or lower for the FC bicycle to travel twice the distance of a lithium-ion-battery-derived bicycle. Using the mathematical model of hydrogen discharge from the MH, the heat transfer of a small MH cartridge for the FC bicycle was investigated. The center of the cartridge cooled by approximately 20 K from the initial temperature, indicating the necessity of heat injection into the MH cartridge even if the initial and boundary temperatures were high. It was also concluded that 83% of the hydrogen charged in the MH could be utilized to maintain the hydrogen flow rate to run a 220 W FC.