Hydrogen Absorption Research Articles

Hydrogen storage and handling with hydrides

Abstract After production and before the use in different applications, hydrogen may need to be purified, transported, compressed and stored. Hydrogen is conventionally stored in high pressure gas cylinders and, as a liquid phase at low temperatures, in opened tanks. These methods present several economic and security problems. So, hydrogen storage in liquid or solid carriers is a suitable method for future applications. Hydrogen absorption and desorption in metal and complex hydrides will be discussed. Examples are provided, including the role of additives in promoting hydrogen sorption reactions. Some case studies using metal hydrides as hydrogen carrier are presented. The HyCARE project, focussed on the development of an efficient metal hydride-based system for the storage of renewables energies is presented, giving evidence of about 50 kg of hydrogen stored in metal hydrides. A small-scale hydrogen refuelling station developed to provide hydrogen for a fuel cell driven drone will be described. The Life Cycle Assessment (LCA) methodology to evaluate the environmental impacts associated with developed systems is also shortly described. Finally, main open challenges will be outlined, suggesting possible approaches for their overcoming.

Effect of Buoyancy Force in Phase Change Material-Based Metal Hydride Reactor

Abstract In Phase Change Material (PCM) simulations, buoyancy force is used to capture the melting contour. However, for the sake of simplicity, most of the PCM-based Metal Hydride (MH) simulations have ignored the influence of buoyancy in PCM which is crucial in analyzing the heat flow within PCM. This study incorporates the buoyancy term in mathematical models to capture the contour of a melted PCM and also its heat transfer capacity during the hydrogen absorption process. A PCM model with buoyancy force is validated against the experimental values and applied to the MH-PCM models. Incorporating the buoyancy force improves the heat transfer rate in the PCM during melting which benefits in better heat removal from the MH bed. Two designs of MH-PCM models having PCM placed in ring-type and tube-type configurations are discussed. Further, the design optimization in ring-type models was done by changing the PCM-MH volume and sandwiching ratios.

The relationship between thermal management methods and hydrogen storage performance of the metal hydride tank

Solid-state hydrogen storage tanks are key equipment for fuel cell vehicles and hydrogen storage. However, the low heat transfer properties of hydrogen storage tanks result in the inability to meet the hydrogen supply requirements of fuel cells. In this study, different thermal management approaches were explored through the design of LaNi5-based solid-state hydrogen storage tanks. We experimentally studied the effects of different internal heat transfer methods, that is, expanded natural graphite (ENG), copper foam, and copper fins on the hydrogen absorption and desorption performance. We also studied the effects of external cooling methods with natural convection, air cooling, and water cooling, respectively. Under the same external cooling method of natural convection, a solid hydrogen storage tank filled with 5 wt.% ENG has similar performance to a tank filled with copper foam. Compared to natural convection, air and water cooling can significantly improve the heating performance of metal hydride (MH) beds by increasing the external heat transfer coefficient. The effect of water cooling is better than that of air cooling, and in these two enhanced performance conditions, the tank filled with copper foam performs better than with ENG. In the case of water cooling, by adding copper fins to a hydrogen storage tank filled with 5 wt.% ENG, the tank was saturated with hydrogen absorption in only 29.4 min, which is 55.6 % shorter than the hydrogen uptake time in a hydrogen storage reactor without copper fins. And its stable hydrogen desorption (1 NL/min) has reached 98.1 % of the total hydrogen released. The results show that the effective thermal conductivity and heat transfer area of metal hydride bed play key roles in improving heat transfer and reaction rate. In addition, heat transfer is more important than mass transfer to improve the performance of the hydrogen storage tank.

An experimental platform for investigation of the Zeeman effect in strong magnetic fields.

An experimental platform is developed for the investigation of the Zeeman effect in strong magnetic fields. Mega-Gauss magnetic fields are generated by a 1 MA Zebra pulsed power machine using metal rod loads. A gas jet or CH oil on the load is the source of hydrogen. Excited hydrogen atoms are backlit by black body radiation from the rod load. Hydrogen absorption spectra are recorded with a grating spectrometer and intensified gated CCD camera. The experimental platform enables the observation of the quadratic Zeeman effect in hydrogen gas jets using the spectral shift of the central line in the Zeeman triplet. Other gases can be studied using the gas jet method.

Hydrogen contribution to low temperature embrittlement during PWR exposure of an alloy 82 weld metal

The embrittlement of alloy 82 welds exposed to a simulated pressurised water reactor (PWR) environment was analysed and compared with that observed for cathodically hydrogen-precharged specimens. Similarities in mechanical behaviour, i.e. the evolution of the constitutive equations with a decrease in flow stress compared with non-precharged specimens, and in the fracture modes, with brittle zones in the outer layer, enabled us to conclude that the embrittlement observed in simulated PWR environment corresponded to a two-step hydrogen-assisted cracking mechanism. The first step corresponded to hydrogen absorption into the surface layer leading to crack initiation, and the second step to hydrogen localisation ahead of the crack tip promoting crack propagation.

Effect of Ce replacing La on the electrochemical performance of amorphous grain boundaries Mg-Ni-based materials

Aiming at enhancing the electrochemical characteristic of RE-Mg-based composite, the partial substituting La with Ce experiment in the composites was conducted, and the surface modification treatment of the alloys was performed by mechanical coating Ni. By means of mechanical trituration, The La10-xCexMg80Ni5 (x = 0–2) + y wt% Ni (y = 50–200) compound materials which have the structures of nanocrystalline and amorphous were synthesized. In order to make sense of the principle action of Ce and Ni elements in structural and electrochemical properties of the material, some deep research were carried out. According to the final results, the as-milled composites have the electrochemical hydrogen absorption and hydrogen desorption abilities at room temperature. Having no use for activation, the as-milled composites can reach the maximum discharge capacities when the first cycling was carried out. With the Ni value x changed from 50 to 200, the discharge capacity was varied from 70.5 mAh/g to 902.1 mAh/g; moreover, the capacity retention rate at 20th cycle (S20) and high rate dischargeability (HRD) of the (x = 0) composite were heightened from 67.2 % to 82.3 %, from 50.6 % to 55.7 % respectively. The composites' (y = 100) discharge capacity has a maximum value 118.5 mAh/g when the Ce value x is 1. The capacity retention rate (S20) is enhanced from 53.3 % to 68.5 % by lifting Ce content from x = 0 to x = 2. what's more, the high-rate discharge ability (HRD), the electrochemical impedance spectrum (EIS), potentiodynamic polarization curves, and potential-step measurements all intimate that substituting La with Ce clearly promotes the composites' electrochemical kinetic properties, but maximum values emerge only when the x value is 1.

Experimental investigation on hydrogen transfer in coupled metal hydride reactors for multistage hydrogen purification application

Three stage metal hydride hydrogen separation system was tested, wherein each stage was configured with 1.2 kg of LaNi4.7Al0.3, LaNi5 and La0.9Ce0.1Ni5, placed in descending order of their equilibrium bed pressure respectively as R1 (La0.9Ce0.1Ni5) > R2 (LaNi5) > R3 (LaNi4.7Al0.3). Hydrogen absorption capacity obtained for R1, R2 and R3 were 15.91 g, 15.93 g and 16.02 g respectively for 3rd activation cycle, performed at 30 bar and 25 °C. For coupled reactor operation, optimum hydrogen transfer was for desorbing reactor at 90 °C and absorbing reactor at 20 °C, which was 12.31 g for R1 to R2 in 350 s, 13.33 g for R2 to R3 in 300 s and 13.38 g for R1 to R2 in 280 s, constituting to 1.03, 1.11 and 1.12 wt% of hydrogen storage respectively. Further, the system was tested for hydrogen purification, wherein inlet sample with 80% impurity (18% Ar, 20% CO2, 20% N2, 20% CH4 and 2% CO) and 20% H2 was used for purification study. According to Thermal Conductivity Detector (TCD) results, the system delivered 91.54%, 99.996% and 99.9999% pure hydrogen respectively for stage 1, stage 2 and stage 3 purification. The system works within low temperature range of 20–90 °C.

Influence of the phase evolution and hydrogen storage behaviors of Mg-based alloy catalyzed by Gd-Fe compound

In order to further optimize the kinetic and thermal properties of Mg-based hydrogen storage alloy, the Mg + 10 wt% GdFe alloy is prepared by using vacuum induction melting. The XRD, SEM, EDS, TEM, PCT and TG-DTA are used to characterize the microstructure of the alloy and phase transition in the reaction process. The results show that the sample is composed of the main phase Mg and the remaining Mg5Gd. In addition, Fe elements are evenly distributed in dissolved in the Mg matrix. After hydrogen absorption, all these phases disappear and are transformed into MgH2 and GdH2. After hydrogen desorption, MgH2 transforms to Mg phase, but the GdH2 phase remains unchanged. During the reaction, Fe always exists in the Mg/MgH2 lattice in the form of simple substance, which is beneficial to the recombination and dissociation of hydrogen atoms. Meanwhile, the GdH2 phase also provides abundant the active sites and diffusion admittance. The alloy has a reversible hydrogen content of 5.8 wt% H2 and an activation energy of 144.1 kJ/mol. It also shows excellent kinetic properties, which can absorb 4.3 wt% H2 at 360 °C in 10 min, and complete hydrogen desorption at the same temperature requires only 18 min. The thermodynamics energy increases only slightly, but the initial hydrogen release temperature and peak temperature are much lower than those of Mg.

Effects of differential speed rolling and H2S poison on hydrogen storage performance of ZK60 alloys ball-milled with C, Pd, Ag, and Zr

The commercial ZK60 magnesium alloy was used to investigate hydrogen absorption performance. The ZK60 alloy was severely deformed via differential speed rolling with differential speeds of 6:3 and 9:3. High energy ball milling was used to blend deformed ZK60 powder with 5 wt% activated carbon(C), 0.5 wt% silver (Ag), 0.5 wt%palladium (Pd), and 1 wt% zirconium (Zr) for 20h at 1725 rpm. Hydrogen absorption characteristics at different low temperatures and number of cycles were analyzed using Sievert's apparatus with hydrogen supplied with H2S impurities. The microstructure of the powder was analyzed field emission scanning electron microscope (FESEM). The hydrogen absorption capacity increases with the temperature rise, and maximum capacity(6.02 wt%) was observed in 5C1Zr deformed at 9:3DSR at 200 °C after five cycles. Hydrogen absorption capacity increases after each hydrogenation cycle in 5C0.5Ag and 5C1Zr but remains the same in 5C0.5Pd. The increase in H2S concentration decreases the hydrogen capacity, and increase in the number of cycles further deteriorates absorption capacity when the differential speed ratio is 6:3. The H2S concentration variation has almost no effect at the differential speed of 9:3. The maximum hydrogen absorption kinetics (74.7%) in 10min was observed in 5C1Zr. A more refined dendritic microstructure was observed in ZK60 alloy deformed with a differential speed ratio of 9:3.

Study of the effect of static stresses on the hydrogen content and electrochemical characteristics of steels of different types

When cathodic protection is applied in places where paint films are damaged, an intense release of hydrogen occurs, which is removed both through diffusion and by transition from the adsorbed state on the metal surface to the subsurface layers thus leading to static hydrogen fatigue of steels, i.e., a brittle fracture occurs suddenly under static loading conditions at stress values significantly lower than the strength limit and even below the plasticity limit. We present the results of studying the impact of static tensile stresses on the hydrogen absorption by a metal during its cathodic polarization and the distribution of hydrogen over the cross-section of the metal surface. Three types of metal samples were used: wire samples made of U8A steel, plate samples made of 10KhSND steel, and semicircular samples made of Kh18N9T stainless steel with a stress concentrator. Tests of wire and semi-ring samples were carried out under a constant load and plate samples were tested under constant deformation. Polarization of wire and plate samples was carried out at different current densities for 4 days and semi-ring samples for 1 hour. At the end of polarization, the layer-by-layer distribution of hydrogen absorbed by the metal was determined by the anodic dissolution method. It is shown that with increasing deformation, the hydrogen content of the surface layers of the metal increases. Moreover, application of tensile loads and deformation of the metal by bending contribute to an increase in the amount of absorbed hydrogen and affect hydrogen distribution over the metal cross section. The thickness of the layer containing the maximum amount of hydrogen differs in steels of different compositions and structures. The results obtained can be used to protect structural steels against corrosion in sea water.

Hydride ion diffusion along grain boundaries in titanium nitride

Density functional theory (DFT) simulations are utilized to study the absorption and diffusion of hydride ions along four types of titanium nitride grain boundaries: open and compact structures of Σ5 (210)[001] and Σ5 (310)[001]. The absorption energy into bulk vacancies ranges from approx. −0.7 eV in TiN0.7 to −0.38 eV for a single vacancy in TiN, and shows a minor dependence on the hydrogen content in the structure. The absorption energy for vacancy sites at the grain boundaries ranges from −0.44 eV to −0.66 eV. Hydrogen absorption into interstitial sites at the grain boundaries is less favourable, in part due to a positive and fairly large zero-point energy contribution, with absorption enthalpies between −0.09 eV and 0.06 eV. The interstitial diffusion barriers are 1.34 eV and 0.83 eV in the open Σ5 (310) and Σ5 (210) grain boundaries, respectively. In the compact grain boundaries, the migrating hydrogen species changed oxidation state from a hydride ion (H0.5−) to a proton (H0.3+) at the transition state as it formed bonds to nitrogen along the diffusion path. The diffusion barriers are larger than in the corresponding open structures: 1.75 eV and 1.02 eV in the compact Σ5 (310) and Σ5 (210) structures, respectively. The considered grain boundaries and diffusion pathways cannot explain the fast interfacial hydride ion transport reported for hydrogen separation membranes based on TiNx thin films with columnar microstructure.

Boosting Hydrogen Storage Performance of MgH2 by Oxygen Vacancy-Rich H-V2O5 Nanosheet as an Excited H-Pump

HighlightsGraphene-like 2D V2O5 nanosheets rich in oxygen vacancies are designed as multi-functional catalysts to fabricate MgH2-H-V2O5 composites.Hydrogen release starts from 185 °C and capacity retention is as high as 99% after 100 cycles at 275 °C.The composites present rapid kinetics and impressive hydrogen absorption capability at near room temperature.The oxygen vacancies could directly enhance kinetics of MgH2 while indirectly exciting “hydrogen pump” effect of VH2/V.

Machine learning assisted design of BCC high entropy alloys for room temperature hydrogen storage

Body-centered cubic (BCC) alloy systems can theoretically store double amounts of hydrogen compared with commercial metal hydrides at room temperature, and BCC high entropy alloys (HEAs) have shown the potential to reach this theoretic limit. However, the high thermodynamic stability of the dihydrides formed during hydrogen storage results in high operating temperatures. Here, by employing multi-objective Bayesian optimization-aided density functional theory calculations, we discovered 8 new HEA candidates for hydrogen storage, including the VNbCrMoMn HEA that can store 2.83 wt% hydrogen at room temperature and atmospheric pressure, vastly exceeding the hydrogen capacities of 1.38 wt% and 1.91 wt% for commercial LaNi5H6 and TiFeH2. Such a high performance of VNbCrMoMn is ascribed to the optimized hydrogen absorption thermodynamics, which is achieved under the guidance of interpretable machine learning which revealed that the thermodynamics of the first and second stages of absorption are largely determined by the bulk modulus and the number of states in the d-band, respectively.

Additively Manufactured Silicone Polymer Composite with High Hydrogen Getter Content and Hydrogen Absorption Capacity.

Hydrogen getters consisting of 1,4-bis[phenylethynyl] benzene (DEB) and a carbon-supported palladium catalyst (Pd/C) have been used to mitigate the accumulation of unwanted hydrogen gas in a sealed system. Here, we report the formulation of a composite resin consisting of silicone polymer plus DEB-Pd/C as an active getter material and the additive manufacturing of silicone getter composites with a high getter content (up to 50 wt %). NMR and DSC studies suggest no reaction between the silicone polymer resin and DEB even at elevated curing temperatures (75 °C). Getter composites with varying amounts of getter and filler were formulated, and their rheological properties were studied. The two composite resins with good printability parameters and different getter contents were chosen to make 3D-printed samples. The hydrogen absorption capacity of these samples was studied at a low hydrogen pressure of 750 mTorr of pure hydrogen. The getter composite with 50 wt% of getter showed normalized DEB conversion of 83%, with the hydrogen adsorption capacity of 100.2 mL of H2 per gram of polymer getter composite.

Influence of Zr Addition on the Microstructure and Hydrogenation Kinetics of Ti50-xV25Cr25Zrx (x = 0, 5, 7, and 9) Alloys.

Due to the poor activation performance and kinetics of Ti50V25Cr25 alloys, the element Zr was added to improve the phase structure of the alloy and achieve a high-performance hydrogen storage alloy. The Ti50-xV25Cr25Zrx (x = 0, 5, 7, and 9) system alloys were prepared by arc melting. The alloys were analyzed using an X-ray diffractometer (XRD), scanning electron microscope (SEM), and differential scanning calorimeter (DSC). The hydrogen storage capabilities of the alloys were also obtained by the Sievert volumetric method. The results indicated that the alloy with Zr added had a combination of the C15 Laves phase and the BCC phase, whereas the Zr-free alloy had a BCC single phase. The partial replacement of Zr with Ti resulted in an increase in the lattice parameters of the main phase. The hydrogen storage kinetic performance and activation of the alloys both significantly improved with an increasing Zr concentration. The time to reach 90% of the maximum hydrogen storage capacity decreased to 2946 s, 230 s, and 120 s, respectively, with the increases in Zr concentration. The initial hydrogen absorption content of the alloys increased and then decreased after the addition of the element Zr. The second phase expanded with an increasing Zr concentration, which in turn decreased the abundance of the BCC main phase. The Ti43V25Cr25Zr7 alloy showed good cycle stability and hydrogen-desorption performance, and it could absorb 90% of the maximum hydrogen storage capacity in around 230 s. The maximum hydrogen-absorption capacity of the alloy was 2.7 wt%. The diffusion activation energy of hydrogen desorption dropped from 102.67 kJ/mol to 92.62 kJ/mol.

Enhanced hydrogen adsorption capability of 2:17-type Sm-Co strips via microstructure modification

The hydrogenation kinetics of Sm26.2CobalFexCu4.0Zr2.3 (x = 23, 27 in wt%) strips (Fe23 and Fe27 strips) has been investigated. The phase composition, morphology, surface roughness and the inner pores of the strips also have been studied by XRD, SEM, optical profilometer and non-destructive micro-computerized tomography. Compared to Fe23 and Fe27 strips, heat-treated strips (H-Fe23 and H-Fe27) and corrosion heat-treated strips (HC-Fe23 and HC-Fe27) exhibit a relatively higher hydrogen absorption capability. Fragmentation behavior occurs in HC-Fe23, H-Fe27 and HC-Fe27 strips during hydrogenation. After heat treatment, the grain size and inner pore size increase, leading to the disappearance of fine crystal strengthening and the concentration internal stress. For corrosion-treated strips, increased surface roughness and deeper grooves result in the formation of surface stress concentration, ultimately leading to an increased susceptibility to hydrogen embrittlement. Accordingly, the increase of grain size, inner pore size and rougher surface is beneficial for hydrogenation and hydrogen embrittlement.

Role of hygroscopic chloride salts on corrosion performance and hydrogen absorption of steel under cyclic wet-dry conditions

The corrosion morphology of steel under aqueous NaCl, MgCl2, and ZnCl2 droplets and the corresponding hydrogen permeation behaviour were investigated using surface characterization techniques and electrochemical methods. Under cyclic wet-dry conditions, Mg2+ and Zn2+-containing surface layers were formed on steel and the latter presented a high corrosion resistance. The most active hydrogen entry occurred under ZnCl2 during drying, while it happened under MgCl2 at low humidity. The effects of chloride salts on the formation of rust layers and hydrogen entry into steel during wet-dry cycles were discussed based on the hardness of metal cations and the deliquescence properties of salts.

Room-temperature sulfur doped NiMoO4 with enhanced conductivity and catalytic activity for efficient hydrogen evolution reaction in alkaline media

Transition metal oxides have been acknowledged for their exceptional water splitting capabilities in alkaline electrolytes, however, their catalytic activity is limited by low conductivity. The introduction of sulfur (S) into nickel molybdate (NiMoO4) at room temperature leads to the formation of sulfur-doped NiMoO4 (S-NiMoO4), thereby significantly enhancing the conductivity and facilitating electron transfer in NiMoO4. Furthermore, the introduction of S effectively modulates the electron density state of NiMoO4 and facilitates the formation of highly active catalytic sites characterized by a significantly reduced hydrogen absorption Gibbs free energy (ΔGH*) value of −0.09 eV. The electrocatalyst S-NiMoO4 exhibits remarkable catalytic performance in promoting the hydrogen evolution reaction (HER), displaying a significantly reduced overpotential of 84 mV at a current density of 10 mA cm−2 and maintaining excellent durability at 68 mA cm−2 for 10 h (h). Furthermore, by utilizing the anodic sulfide oxidation reaction (SOR) instead of the sluggish oxygen evolution reaction (OER), the assembled electrolyzer employing S-NiMoO4 as both the cathode and anode need merely 0.8 V to achieve 105 mA cm−2, while simultaneously producing hydrogen gas (H2) and S monomer. This work paves the way for improving electron transfer and activating active sites of metal oxides, thereby enhancing their HER activity.

Hydrogen uptake kinetics of cathodic polarized metals in aqueous electrolytes

We use a unique combination of electrochemical techniques to elucidate the dependency of hydrogen evolution reaction (HER) and absorption on pH and overpotential for iron and nickel. Impedance spectroscopy shows the dominance of the Volmer–Heyrovsky reaction pathway, challenging the common consideration of Volmer–Tafel dominance. Polarization slopes agree with the Volmer or Heyrovsky rate-determining step, with limitations at high overpotential. The evolution of steady-state permeation current density with overpotential is rationalized through newly-developed theory. Surface activity and absorption trends are captured. Combined with modelling, this work provides a path for quantifying hydrogen uptake and establishing an equivalent fugacity for aqueous electrolytes.

Effect of different metal element substitution on microstructural and comprehensive hydrogen storage performance of Ti0·9Zr0·1Mn0·95Cr0·7V0.2M0.15 (M = Fe, Co, Ni, Cu, Mo) alloy

Hydrogen is now being used as a renewable clean energy carrier. One of the main issues with the application of hydrogen energy is a shortage of security and efficient hydrogen storage technology. TiMn-based alloys are considered promising hydrogen storage materials, but their comprehensive hydrogen storage properties and cyclic stable performance limit their further practical application. The hydrogen storage properties of alloys can be enhanced by substituting transition metal elements. Therefore, the comprehensive hydrogen storage performance of the Ti0·9Zr0·1Mn0·95Cr0·7V0.2M0.15 (M ​= ​Fe, Co, Ni, Cu, Mo) alloys was systematically investigated according to the Mn element on the B side is partially replaced by variety of transition metal elements. The M ​= ​Ni alloy, which showed the highest hydrogen storage capacity among the group of alloys, was used to explore cycle stability. The plateau pressures of the series alloys decreased in order, Fe ​> ​Co ​> ​Ni ​> ​Cu ​> ​Mo. Aspects of hydrogen absorption kinetics, all of the alloys can reach full hydrogen absorption saturation within 400 ​s at 303 ​K. The Ti0·9Zr0·1Mn0·95Cr0·7V0·2Mo0.15 alloy possessed the fastest hydrogen absorption kinetic rate (t0.9 ​= ​65 ​s) and the smallest hysteresis factor. This suggests that the substitution of Mo elements is effective in improving the hysteresis of the Laves phase alloys. Among the series of alloys, the M ​= ​Ni alloy exhibited the best overall hydrogen storage performance, which hydrogen storage capacity can reach 1.81 ​wt% and 97% of its capacity is kept after 100 cycles.