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The number of catalytically active sites (site density, SD) and the catalytic turnover frequency (TOF) are critical for meaningful comparisons between catalytic materials and their rational improvement. SD and TOF numbers have remained elusive for PGM-free, metal/nitrogen-doped porous carbon electrocatalysts (MNC), in particular, FeNC materials that are now intensively investigated and widely utilized to catalyze the oxygen reduction reaction (ORR) in fuel cell cathodes. Here, we apply CO cryo sorption and desorption to evaluate SD and TOF numbers of a state-of-art FeNC ORR electrocatalyst with atomically dispersed coordinative FeNx (x ≤ 4) sites in acid and alkaline conditions. More specifically, we study the impact of thermal pretreatment conditions prior to assessing the number of sorption-active FeNx sites. We show that the pretreatment temperature sensitively affects the CO sorption uptake through a progressive thermal removal of airborne adsorbates, which, in turn, controls the resulting catalytic S...

MCM-48, metal doped MCM-48 and MCM-41 have been synthesized by hydrothermal method, respectively. The specific hydrogen storage amount of prepared materials at 77 K below 100 kPa are recorded in order to explore their hydrogen storage mechanisms. Experimental results indicate that pore size is the key factor that dominates their hydrogen storage capacity. Adsorption plays an important role from 0 to 35 kPa and mesoporous materials with smaller pore size seem to be better candidates for hydrogen storage. Diffusion will play a dominant role in the pressure range of 35–100 kPa, and mesoporous materials with larger pore size exhibit higher hydrogen storage capacity.

In this study, activated polymer-based hard carbons were prepared using various steam activation conditions in order to enhance their hydrogen storage ability. The structural characteristics of the activated carbons were observed by X-ray diffraction and Raman spectroscopy. The N2 adsorption isotherm characteristics at 77 K were confirmed by Brunauer-Emmett-Teller, Barrett-Joyner-Halenda and non-local density functional theory equations. The hydrogen storage behaviours of the activated carbons at 298 K and 10 MPa were studied using a Pressure-Composition-Temperature apparatus. From the results, specific surface areas and total pore volume of the activated carbons were determined to be 1680–2320 m2/g and 0.78–1.39 cm3/g, respectively. It was also observed that various pore size distributions were found to be dependent on the functions of activation time. In the observed result, the hydrogen adsorption of APHS-9-4 increased about 30% more than that of as-prepared hard carbon. This indicates that hydrogen storage capacity could be a function not only of specific surface area or total pore volume, but also of micropore volume fraction in the range of 0.63–0.78 nm of adsorbents.

LaNi 5 -based hydrogen storage alloys have a strong application potential in many areas such as gaseous hydrogen storage, hydrogen compressing, Ni/MH batteries etc. But the cycling stability is always an important issue of concern. In this study, the changes in the hydrogen storage performance of the LaNi 4 Al alloy at 403, 423 and 443 K during 1000 hydrogen absorption/desorption cycles are studied, and the degradation mechanism is explored using EXAFS as a main study method. It is found that with increasing cycle number, the P-C-T plateau first becomes flattened then steepened, the plateau pressure and the hysteresis are decreased, the entropy change for both hydrogen absorption and desorption first increases and then decreases, and the hydrogen storage capacity decreases. Testing temperature does not have notable influence in the variation trend of the long-term hydrogen storage properties. The degradation is mainly reflected by the tilted P-C-T plateau and the reduced hydrogen storage capacity. Structural analysis results suggest that the strain-induced nanocrystalization and the atomic mis-location during hydrogen absorption/desorption might cause a high disorder state and a partial destruction in LaNi 5 crystal lattice, resulting in the degradation in the hydrogen storage properties.

Effects of Mn doping on the hydrogen adsorption and diffusion on the Mg 2 Ni (010) surface are studied using first-principles density functional theory. The results show that the Mg 2 Ni (010) surface becomes more uneven and the thermodynamical stability of Mg 2 Ni (010) system is lowered after Mn doping. Analysis of the hydrogen adsorption energies on the pure and Mn-doped Mg 2 Ni (010) surfaces shows that Mn-doped Mg 2 Ni (010) surface has more sites for hydrogen to adsorb stably. Further calculation of the hydrogen diffusion indicates that the substitution of Mg with Mn lowers the energy barrier for hydrogen to diffuse from the (010) surface to the subsurface.

Metal hydrides have been under focus as a favorable hydrogen storage medium. The heat transfer to/from the metal hydride reactor bed is one of the major controlling parameters of the storage process. Consequently, a variety of heat transfer techniques have been employed till date to improve the system performance. In this review, an effort has been made to summarize the developments so far, assess the effectiveness of various heat transfer techniques and draw some inferences from the study which can contribute to a more effective design of heat transfer systems. Upon a comprehensive study of the existing literature a classification of heat transfer techniques was attempted and their relative effectiveness assessed with respect to system scale. It was observed that improvement of only thermal conductivity or heat transfer coefficient will not be able to improve system performance. An effective design should take into account the influence of both these parameters concurrently.

Hydrogen produced from ethanol solution by pulsed discharge was investigated in this work. With needle-net configurations, hydrogen can be easily exported from the plasma reactor thereby preventing hydrogen from consuming by the oxidizing active substances generated from pulsed discharge. Both flow rate and percentage concentration of hydrogen were enhanced with the increase of energy density, but not much change with the increase of discharge time. Flow rate, percentage concentration, and energy consumption of hydrogen were achieved about 800 mL/min, 73.5%, and 0.9 kWh/m3 H2 respectively with energy density of 6.4 J/L. All products were analyzed, which were divided into main and secondary products guiding the mechanism analysis of hydrogen production. The main products contain H2, CO, CH3OH, and the secondary products include C2H2, CO2, macromolecular compounds, nano carbon particles. The high hydrogen yield, emerged nano carbon, low ethanol and energy consumption make this method possess bright prospect in hydrogen production.

The development of a viable hydrogen storage system is one of the key challenges which must be solved prior to the establishment of a hydrogen economy. One of the envisaged options to store hydrogen is adsorption on high surface area porous materials such as activated carbons (ACs). The aim of the present study is to develop a low cost hydrogen storage material and to improve its uptake capacity at room temperature. First, an activated carbon has been prepared from olive pomace through chemical activation procedure. Then, the carbon surface has been decorated with oxygen functional groups and with metal nanoparticles. A careful textural characterizations show that, in contrast to other gases, oxygenated groups hindered H2 access to active adsorption sites. Hence acid activation should be avoided for hydrogen adsorbent preparation. While, the insertion of metal nanoparticles improve the H2 adsorption performance of AC via spillover mechanism at room temperature, unless the metal content and the catalyst preparation method were optimized.

Hydrogen sulfide is a hazardous gas from environmental, human health and equipment prospective. Hydrogen sulfide occurs naturally from crude oil and natural gas wells along with some other hydrocarbon impurities. Reformation of hydrogen sulfide without or with the presence of xylene (a common impurity present in hydrogen sulfide) has been investigated. Production of hydrogen concurrent with destruction of hydrogen sulfide provides a good alternative method to treat hydrogen sulfide. The role of xylene addition on the reformation of hydrogen sulfide was experimentally investigated. A laboratory-scale reactor was used to examine the effect of reactor temperature in the range of 1273–1573 K and various inlet stream composition on the production of hydrogen and destruction of both hydrogen sulfide and xylene. Results showed enhanced hydrogen production and higher hydrogen sulfide destruction at temperatures above 1273 K. Xylene was destructed completely at a relatively low temperature of 1373 K. Carbon disulfide formation increased with increase in temperature for all the inlet compositions of hydrogen sulfide and xylene examined. Reducing the formation of CS 2 and also mitigation of carbon deposition by reducing the amounts of carbon introduced to the reactor were investigated and quantified experimentally. The most favorable operational conditions for reaction between hydrogen sulfide and xylene were established. The results showed new potential of this binary mixture dissociation as an alluring treatment method of hydrogen sulfide.

In this work, hydrogen storage property of single walled carbon nanotubes-tungsten trioxide (SWCNTs-WO 3 ) composite is investigated. The composite is prepared and hydrogenated by electron beam (e-beam) evaporation technique. Hydrogenation is carried out during the preparation of the composite itself. The amount of hydrogen uptake by the composite is 2.7 wt%, which is due to the collective adsorption of hydrogen by CNTs and WO 3 nanostructured materials, the method of preparation and hydrogenation involved. The incorporated hydrogen is completely (100%) released in the temperature range of 175–305 °C which in turn infers that the hydrogenated composite is stable at room temperature. The stored hydrogen has the average binding energy of 0.4 eV and the nature of binding is found to be weak chemisorption. Spillover mechanism is attributed for the hydrogen uptake of the composite.

The production of pure hydrogen for use in energy applications and related industries often relies on the permeation of hydrogen through palladium-based membranes. However, the scarcity of Pd reserves necessitates the development of affordable alternatives with high hydrogen permeability. Here we report room-temperature hydrogen permeability of titanium nitrides (widely used as tough and inert coating materials) enabled by mixed hydride ion–electron conductivity. Combined spectroscopic, permeability and microgravimetric measurements reveal that nanocrystalline TiN x membranes feature enhanced grain-boundary diffusion of hydride anions associated with interfacial Ti cations on nanograins. Since the corresponding activation energies are very low (

The lightweight compound material NaNH2-NaBH4 is regarded as a promising hydrogen storage composite due to the high hydrogen density. Mechanical ball milling was employed to synthesize the composite NaNH2-NaBH4 (2/1 molar ratio), and the samples were investigated utilizing thermogravimetric-differential thermal analysis-mass spectroscopy (TG-DTA-MS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses. The full-spectrum test (range of the ratio of mass to charge: 0-200) shows that the released gaseous species contain H2, NH3, B2H6, and N2 in the heating process from room temperature to 400 °C, and possibly the impurity gas B6H12 also exists. The TG/DTA analyses show that the composite NaNH2-NaBH4 (2/1 molar ratio) is conductive to generate hydrogen so that the dehydrogenation process can be finished before 400 °C. Moreover, the thermal decomposition process from 200 to 400 °C involves two-step dehydrogenation reactions: (1) Na3(NH2)2BH4 hydride decomposes into Na3BN2 and H2 (200-350 °C); (2) remaining Na3(NH2)2BH4 reacts with NaBH4 and Na3BN2, generating Na, BN, NH3, N2, and H2 (350-400 °C). The better mechanism understanding of the thermal decomposition pathway lays a foundation for tailoring the hydrogen storage performance of the composite complex hydrides system.

Hydrogen storage in single-walled carbon nanotubes containing the Stone-Wales defects and doped with metal atoms (titanium and beryllium) has been studied using molecular dynamics simulations and density functional theory calculations. Although, Be is known to be toxic at high temperatures, Be-doped SWCNT shows a promising potential to exceed the DOE target at moderate temperatures and pressures. One of the major advantages of doping Be is its lower atomic weight, which increases the gravimetric storage capacity compared to SWCNTs doped with heavy-wight Ti atoms. In addition, the binding energy of Be is higher than that of Ti, which enhances the capture of hydrogen molecules. The gravimetric and volumetric storage capacities depend not only on the dopant atom but also on the location of doping. SWCNTs in which Be is doped on the octagonal ring of the Stone-Wales defects exhibits higher storage capacity than Be doped on defect-free SWCNTs. At room temperature (298 K), the storage capacity of Be-doped SWCNT containing the Stone-Wales defect exceeds the DOE target of 5.5 wt% (gravimetric) and 40 g H 2 /L (volumetric) at a pressure of 267 atm, which is significantly lower than that used in high pressure vessels.

In situ hydrogen production technologies have attracted attentions because of hydrogen storage and transportation safety issues. Discharge plasma technology for hydrogen production is of fast response, large capacity, small scale and portability, which is suitable for automobiles and ships. In this paper, a method for producing hydrogen by microwave discharge in ethanol solution was introduced. A microwave discharge reactor of direct standing wave coupling (MDRSWC) was designed, which was suitable for on-board hydrogen production. The characteristics of large capacity hydrogen production by applying MDRSWC in liquid ethanol were investigated. Depending on the experimental conditions of ethanol concentration and microwave power, the flow rate of hydrogen production was achieved ranging from 28.93 to 72.48 g/h. In addition to main hydrogen and carbon dioxide, a small amount of methane and acetylene as by-products were detected. By optimizing the experimental conditions, the experimental results showed that the flow rate of hydrogen, the percentage concentration of hydrogen and the energy yield of hydrogen production were 72.48 g/h, 58.1% and 48.32 g/kWh respectively. This work could provide a potentially effective hydrogen production method for on-board hydrogen utilization device.

Hydrogen (1H) trapped at intermetallic particles (IPs) in an aluminum alloy, 6061-T6, was visualized with secondary ion mass spectrometry (SIMS) by precisely excluding the false signal which is caused by background hydrogen (HBG). The interference of the HBG was avoided by a unique continuous pre-sputtering (pre-digging) by a primary ion beam of SIMS into a sample in combination with silicon sputtering prior to the SIMS measurement of the sample and we succeeded in visualizing the exact signal of 1H trapped by IPs at subsurface layer of the sample charged in high-pressure hydrogen gas. The thermal desorption analysis clarified that the desorption energy (Ed) of the IPs was 200 kJ/mol or higher, which was extremely higher than Ed for lattice interstice, dislocations, and vacancies. High density hydrogen was concentratedly trapped at IPs in the subsurface layer in contact with the hydrogen gas. This nature causes an extremely low effective hydrogen diffusivity of 6061-T6 of the order of 10−14 m2/s even at 200 °C and may eventually give a high HE resistance to 6061-T6.

Hydrogen can be stored in containers or in materials (in molecular or atomic forms). The atomic form can further exist as multiple phases. Molecular hydrogen can be adsorbed on the surface or can be present inside the material. By invoking multiple modes of hydrogen storage, we establish a paradigm shift in the philosophy of hydrogen storage. Using a novel strategy of storage of molecular hydrogen in metal (Pd) nanocontainers, we observe that 18% hydrogen is in molecular form. Interestingly, this is achieved at 25 °C and 1 atm pressure; which is in contrast to storage in MOFs and carbonaceous materials like nanotubes. Enhancement in storage capacity as compared to Pd nanocrystals of the same mass is observed (36% increase at 1 atm & 25 °C), along with fast kinetics (0.5 wt% hydrogen absorption in 5 s). A new mechanism for hydrogen storage involving the dual catalytic role of Pd is established.

Schwarzites are one of the most well-known forms of nanoporous carbon. High porosity and large surface area of these materials make them promising candidates for molecular hydrogen storage. Quantum-chemical modeling showed that hydrogen weight fraction inside D-schwarzite structure depends on the number of atoms per unit cell that determines its size and morphology. D480 schwarzite has demonstrated the largest value of hydrogen sorption capacity amongst the structures considered in this work. It reaches 7.65% at the technologically acceptable values of temperature and pressure (300 K and 10 МPа). Though being lower than that required by DOE (9%), this amount can be increased by using schwarzites with larger unit cell corresponding to the larger surface area.

Development of technologically and economically feasible solutions for hydrogen storage stimulates progress in hydrogen economy. High gravimetric and volumetric capacities of magnesium hydride makes it promising material capable to accelerate implementation of hydrogen-based technologies in our daily life. However, widely discussed limitations of sorption kinetics and thermodynamic properties must be managed in MgH 2 . This work investigates two steps hydrogenation when process of hydrogen absorption is followed after hydrogen plasma activation. Such technique initiates creation of new channels for enhanced hydrogen sorption. Moreover, synthesis of negligible amount of hydride acts as positive factor for further hydrogenation.

We investigated the minimum energy pathways and energy barriers of reversible reaction (V111 + H2↔V221) based upon calculations using density functional theory. We find a comparable activation barrier of around 1.3 eV for both the dissociative chemisorption and desorption processes. The charge transfer rate from a reacting hydrogen atom to the graphene is around 0.18 e per hydrogen atom in the final state. A subsequent reaction path to recover the initial structure of V111 is realized by the migration of hydrogen atoms from V221 onto the graphene surface. The comparable energy barrier of 1.3 eV for both adsorption and desorption suggests that this novel storage and release concept has the potential to act as a hydrogen storage system for certain applications.

The present numerical study aimed at studying the solid-statehydrogen storage and destocking in the Lanthanum Nickel (LaNi5 H2) in a concentric triple-tube heat exchanger. Moreover, the influence of the thermal-reactor geometry for the storage and destocking hydrogen have been examined by changing the diameters of the heat exchanger. The performance of Lanthanum Nickel was compared with those of the hydride (MmNi4.6Fe0.4) and activated carbon. The flowing parameters: kinetics of hydrogen absorption/desorption, chemical reactions, enthalpy of fusion, equilibrium pressure, hydrogen concentration and the storage capacity were considered for calculating the terms of mass and energy equations. The hydride thermal and mass behaviour was integrated in the CFD Fluent with software (C++). A good agreement between the presented model and the literature experimental results was obtained. Additionally, the mentioned above parameters have shown a significant impact on the geometry of the reactor.

Solar water splitting is an effective approach to hydrogen production and application of solar energy. However, the photo-generated hydrogen should be initially stored in high pressure cylinder and subsequently applied in hydrogen-oxygen fuel cells. Herein, a solar rechargeable battery is proposed based mainly on hydrogen storage mechanism in dual-phase electrolyte. Specifically, the hydrogen production, storage and utilization are integrated into a hybrid system of the dye-sensitized solar cell and electrochemical cell with the dye-sensitized TiO 2 as photo-anode, LiI as the cathode active material in organic electrolyte, AB 5 -type hydrogen storage alloy as anode in alkaline solution, and PEDOT-modified Nafion membrane as separator. Here, the photo-generated electrons in organic electrolyte pass to the AB 5 -type hydrogen storage alloy to split water in alkaline aqueous electrolyte for generating hydrogen, which is in situ stored into AB 5 -type hydrogen storage alloy. Subsequently, the hydrogen stored in the AB 5 -type hydrogen storage alloy can be oxidized by electrochemical way to generate electricity, coupled with LiI cathode in organic electrolyte. The solar rechargeable battery demonstrates a new solution of the solar energy conversion, hydrogen production, storage, and utilization, achieving the new energy conversion and storage from solar energy to chemical energy, and further to electrical energy.

The paper shows, that a low-temperature plasma initiated in liquid media in interelectrode discharge gap is able to decompose hydrogen containing organic molecules resulting in obtaining gaseous products with volume part of hydrogen higher than 90% (up to gas chromatography data). Tentative assessments of energy efficiency, calculated with regard for hydrogen and feedstock heating value and energy consumption, have shown efficiency factor of 60–70%, depending on the source mixture composition. Theoretical model calculations of discharge current and voltage have been performed; the values are in good accordance with experimental data.

A potential hydrogen source generated from milled Li-Si-AlCl3 composite was evaluated in this paper. The composite exhibits good hydrogen generation performance in water at 313–343 K, whereas pure silicon powder cannot continuously react with water under similar conditions. The hydrogen yield reaches 1300 mL hydrogen/g within 20 min, and the highest hydrogen generation rate is higher than 1200 mL hydrogen/g min within the first minute of hydrolysis. The hydrogen generation performance increases with increasing concentrations of lithium and aluminum chloride. Microstructure analysis indicates that silicon activity increases due to decreased particle size and distribution of lithium and aluminum chloride into silicon matrix during milling. The hydrolysis of the additives generates heat and alkaline hydrolysis byproducts, thereby stimulating the hydrolysis rate of silicon in the micro area. Therefore, the hydrolysis of silicon in water may act as a potential hydrogen source for portable micro fuel cells.

The article addresses the determination of the physical and material properties of the alloy La0.85Ce0.15Ni5 with a crystalline structure. The properties of the microstructure of the alloy were determined using a scanning electron microscope. The chemical composition was evaluated by energy-dispersive X-ray spectroscopy. An X-ray diffractometer was used to determine the phase composition of the alloy. Next, the alloy sample was subjected to measurements of hardness, thermal conductivity and heat capacity. The storage capacity of hydrogen in the alloy was determined using the pressure concentration isotherms method of measuring. For comparison, the storage capacity was also measured in the amorphous structure of the alloy formed by the melt spinning method.

Metal hydride (MH) alloys are a promising type of material in hydrogen storage applications, allowing for low-pressure, high-density storage. However, while many studies are being performed on enhancing the hydrogen storage properties of such alloys, there has been little research on large-scale storage vessels which make use of the alloys. In particular, large-scale, high-density storage devices must make allowances for the temperature variations caused by the heat of reaction between hydrogen and MH alloys, which may impact the storage characteristics. In this study, we propose a numerical model for the design and evaluation of hydrogen storage devices using MH alloys. Hydrogen desorption reaction behavior for an alloy is observed in terms of temperature and reaction rate. This behavioral correlation is used as the basis for a comprehensive simulation model of the alloy system. Calculated results are found to be in good agreement with experimentally measured data, indicating that the model may be applied to multiple system geometries, scales, and alloy compositions.

In this paper, we give an overview of recent advances in the production of formic acid, as a hydrogen carrier, from CO 2 and water by using the earth-abundant metal of Fe as the reductant under hydrothermal conditions, which mainly includes: 1) hydrogen production from water with Fe; 2) reduction of HCO 3 – to formic acid in the presence and absence of catalysts; 3) proposed reaction mechanisms. The novel options under this study are mainly the use of water as a hydrogen source with metal Fe as a reductant, and the formed Fe x O y as an auto-catalyst. Such a process possesses several benefits: (i) water acts not only as a hydrogen source but also as an environmentally benign solvent; (ii) there are no hydrogen requirements, including pumps or storage, because hydrogen is derived from water and reacts with CO 2 in situ ; (iii) no exotic catalysts or harsh reagents are used; and (iv) the method is simple and highly efficient. This technology can provide a one-step, sustainable and highly efficient way to reduce CO 2 into formic acid using the hydrogen directly from water.

Using density functional theory, we investigated the hydrogen storage capacity of Li coated BC3 honeycomb sheet. Our result indicates 18 H2 molecules can be adsorbed on BC3Li6 complex with a storage gravimetric density of 9.68 wt% and the average adsorption energy reaches 0.206 eV/H2. This is desirable for absorbing and desorbing H2 molecules at near ambient conditions.

We report a simple method of entrapping hydrogen gas inside palladium silica material (Pd/MCM-41). Nuclear Magnetic Resonance spectroscopy shows water can be used as a simple mechanism for entrapping and releasing hydrogen gas in this material. For dry samples of Pd/MCM-41 loaded with hydrogen gas at 2 atm, the 1 H-NMR gas signal continued to attenuate and eventually disappeared after approximately 17 min. In contrast, adding water to a dry sample of Pd/MCM-41 loaded with hydrogen gas entrapped the hydrogen into the sample. In this case, the 1 H-NMR signal of the gas remains unchanged for up to a week. In addition, removing the water caused the hydrogen gas to start leaving the material. This is an essential step toward finding an easy way to store/release hydrogen gas at pressures close to the atmospheric value in metallic based porous materials.

Metal hydride (MH) material can be used for effective separation of hydrogen from gas mixture. However, some impurities in the feedstock gas may cause the poisoning of the material and hence failure of the MH-based hydrogen separation system. In this paper, the hydrogen storage alloy LaNi 4.3 Al 0.7 , which has low-plateau pressure and was supposed to be used for hydrogen separation from the semi-coke oven gas, was tested in the atmosphere with relatively high concentration of CO impurities (∼0.1%v/v) by cycling experiments. Interestingly, the hydrogen storage capacity of the material shows quite mild decline during contact with CO at the temperature of 363 K or higher, and relatively fast kinetics can be kept, highlighting its application potential for hydrogen separation on a variety of occasions.

The MgH2 with 16.7 wt.% BiVO4 composite prepared by ball milling method presented favorable thermodynamic and kinetic performances, and the effect of BiVO4 on the hydrogen storage properties of MgH2 was investigated. The onset desorption temperature of the composite is 538 K, 98 K lower than that of the as-milled MgH2. The composite releases 1.1 wt.% hydrogen at 573 K within 1200 s, while pristine MgH2 hardly release hydrogen under identical conditions. Moreover, the composite absorbs 1.99 wt.% hydrogen at 423 K, 2.12 times than that of pristine MgH2. The dehydrogenation activation energy of MgH2 is reduced from 122.29 kJ/mol to 84.33 kJ/mol with the addition of BiVO4. The BiVO4 additive also facilitates the H diffusion and alters the rate-controlling step of MgH2 in the hydrogen absorption process. It may be believed that the active V-containing species formed during the dehydrogenation process would greatly improve the hydrogen storage performances of MgH2.

Hydrogen is regarded as an ideal fuel for vehicle applications owing to its high chemical energy. However, for on-board energy storage, fuel cell electric vehicles need compact, light, and affordable hydrogen storage system to replace the pressurized hydrogen tanks. In this regard, various materials and composites have been developed for denser and safer hydrogen storage. Among them, Mg is considered as a highly promising material to store the hydrogen in terms of gravimetric and volumetric capacity. However, because of its higher thermodynamic stability and sluggish hydrogen sorption kinetics, the sorption temperature is high and the sorption time is long, limiting for practical usage. Nanoscale material designs with various dimensionalities that have been extensively studied and used in countless research and development sectors, which can provide new strategies to tackle the limitations of Mg based hydrogen storage system. This review describes the fundamental properties, preparation, activation kinetics and thermodynamic stability of various nanostructured Mg/MgH2 materials (including bulk particles, nanofilms, nanowires and nanoparticles confined in nanoporous carbon structures and encapsulated by polymers) for feasible hydrogen storage applications, and summarizes their dimensional effects.

Synthesis of a mathematical model of cooling of supercharging gas in the vapor space of cryogenic tanks containing liquefied gas is studied. Based on the model of a unidimensional dynamic thermal boundary layer, it is shown that the heat flux through the free liquid hydrogen surface in the cryogenic tank having a vapor space supercharged with gaseous hydrogen is much less than the heat flux through a wetted surface. The operational process of supercharging vapor space with gaseous hydrogen is studied by the example of a commercial liquid hydrogen tank. An example of calculation that shows the procedure of calculation of specific heat fluxes is given. The calculation results show that in the working range of fractions of the vapor space the heat flux through the liquid surface is much less than the heat flux through a wetted surface and that the heat of the supercharging gas exerts practically no influence on the change in temperature of the cryogenic liquid during its storage in the tank.

Increasing the amount of hydrogen that is electrochemically inserted into materials is important for studying superconductivity and hydrogen embrittlement, and improving hydrogen storage capabilities. Surfaces can be engineered to accomplish this task with better insight into how the composition of a material's first few atomic layers affects the electrochemical insertion of hydrogen. To this end, different amounts of Pb were added to the 0.1 M LiOH electrolyte to be deposited onto Pd cathodes during galvanostatic experiments. The investigated amount of added Pb was between 1 μg cm−2 and 23 μg cm−2 with respect to the geometric area of the Pd cathode. The optimum surface doping level 2.9 μg cm−2 of Pb (∼1.4 mass equivalent monolayers) was found to achieve the highest quantity of inserted hydrogen at approximately −0.5 V vs RHE. Additionally, the hydrogen content increased from PdH0.75 to PdH0.86 with increasing Pb amounts up to 2.9 μg cm−2 at a constant current of −14.5 mA cm−2. For comparison, the same change in hydrogen content from pressurized gas loading experiments would require an increase in hydrogen fugacity from about 6 to 1420 atm. Preliminary analysis concerning the adsorbed hydrogen chemical potential suggests the Pb is affecting the balance between the Volmer, Heyrovsky, and Tafel reaction rates, which changes the hydrogen surface chemical potential, and ultimately controls the hydrogen insertion. Furthermore, the addition of Pb was found to decrease the rate of hydrogen insertion. This work provides a fundamental basis for the future design of metal surfaces yielding enhanced electrochemical hydrogen insertion in Pd and other hydrogen absorbing materials.

Development of novel carbon-based nanoporous materials with high reversible capacity and excellent cycling stability is a hot topic in the field of hydrogen delivery and storage. In this work, first-principles calculations are carried out to discuss the hydrogen storage properties of Li-decorated porous graphene (Li-PG). The binding energies, electronic structures, storage capacities of hydrogen on different sites are investigated in details. The computational results show that with the increase of lithium doping concentration, the electron concentration of donor atoms exceeds the Nc value, and as a consequence, the PG changes from the p-type semiconductor to the n-type degenerate semiconductor. The maximum hydrogen adsorption configurations of H1a-H'1b and H2a-H'2b systems are obtained, and the average binding energy of per H2 molecule is 0.245 eV and 0.263 eV, respectively. Furthermore, ab inito MD simulation results show that the H1-H'1 and H2-H'2 systems can hold up to sixteen and fifteen H2 molecules, which corresponds to a hydrogen storage capacity of 10.89 wt% and 10.79 wt% at T = 300 K (no external pressure), respectively.

This work illustrates the hydrogen storage performance of Zr(V0.95Ni0.05)2 Laves phase alloy in hydrogen with/without gaseous impurities. It is found that Zr(V0.95Ni0.05)2 can be activated in either pure hydrogen or hydrogen with 1.00 vol% O2. However, the activation of Zr(V0.95Ni0.05)2 in hydrogen with gaseous impurities requires much more time and higher temperature due to the continually forming passivation layer oxides. Hydrogen storage capacity is found to degrade evidently with increasing oxygen content and the alloy almost loses entire hydrogen absorption capacity in hydrogen with 2.00 vol% O2. During absorption/desorption cycles, the maximum hydrogen capacity against gaseous impurities decreases in various degree comparing to that in pure hydrogen. At the temperature below 423 K, the hydrogen desorption capacity decreases gradually with increasing absorption/desorption cycles. The alloys can hardly absorb hydrogen in the third cycle both at 308 and 423 K. With the further increase of temperature, the hydrogen absorption capacity at the first cycle even shows a little rise at 573 K comparing with that at 308 K, indicating a strong temperature dependence of the hydrogen storage degradation against gaseous impurities. Both the kinetics and capacity of Zr(V0.95Ni0.05)2 decrease to a certain extent after 3 absorption/desorption cycles at 723 K.

Single-walled carbon nanotubes (SWCNTs, the mean diameter of 1.35 nm) were produced by a modified arc discharging furnace using a mixture powder of KCl and Co-Ni alloy as catalyst at 600°C. The hydrogen storage capacity of SWCNTs was enhanced by the mechanism of atom hydrogen spillover from the supported catalyst. The temperature effect on the hydrogen storage capacity of as-grown SWCNTs was investigated. The relative experiments of SWCNT hydrogen uptake and release were carried out by a high-pressure volumetric gas-adsorption measurement system. The experimental results indicated that the hydrogen storage capacity of SWCNTs increased with the environmental temperatures decreasing. The hydrogen storage capacity of SWCNTs was up to 1.73 wt% at 77 K for 2 hours under the pressure of 10 MPa, and the corresponding releasing hydrogen capacity is about 1.23 wt% under ambient pressure.

Cross-linked porous polymeric complexes with exposed metal sites are synthesized for room temperature hydrogen storage via physisorption. At 298 K and 100 atm, PTF-Cr exhibits high excess hydrogen storage capacity up to 1.5 wt% with Qst of 11.5 kJ mol−1 while PTF-Mg exhibits 0.5 wt% with Qst of 8 kJ mol−1. The result provides insight for development of future storage materials with exposed transition metals.

Hydrogenated diamond-like carbon films produced by C 3 H 6 deposition at 5 kV and implanted at room temperature with 30 keV Co atoms to 12 at.% show not only a bimodal distribution of Co atoms but also a massive redistribution of hydrogen in the films. Resonant nuclear reaction analysis was used to measure the hydrogen depth profiles (15N-method). Depletion of hydrogen near the surface was measured to be as low as 7 at.% followed by hydrogen accumulation from 27 to 35 at.%. A model is proposed considering the thermal energy deposited by collision cascade for thermal insulators. In this model, sufficient energy is provided for dissociated hydrogen to diffuse out of the sample from the surface and diffuse into the sample towards the interface which is however limited by the range of the incoming Co ions. At a hydrogen concentration of ∼35 at.%, the concentration gradient of the mobile unbounded hydrogen atoms is neutralised effectively stopping diffusion towards the interface. The results point towards new routes of controlling the composition and distribution of elements at the nanoscale within a base matrix without using any heat treatment methods. Exploring these opportunities can lead to a new horizon of materials and device engineering needed for enabling advanced technologies and applications.

We use the first-principles calculation based on density functional theory (DFT) to investigate the hydrogen storage on Li 12 F 12 nano-cage. Our result indicates the largest hydrogen gravimetric density is 7.14 wt% and this is higher than the 2017 target from the US department of energy (DOE). Meanwhile, the average adsorption energy is −0.161 eV/H 2 , which is desirable for absorbing and desorbing H 2 molecules at near ambient conditions. These findings will have important implications on designing hydrogen storage materials in the future.