Hydrogen Absorbing Materials Research Articles

Porous Silicone Rubber Composite Supported 1,4-Diphenylethynyl Benzene for Hydrogen Absorption with Pd/C Catalyst.

Hydrogen is a dangerous gas as it reacts very easily with oxygen and may explode; therefore, the accumulation of hydrogen in confined spaces is a safety hazard. Composites consisting of unsaturated polymers and catalysts are a common getter, where the commonly used polymer is 1,4- diphenylethynyl benzene (DEB). Silicone rubber (SR) is a good carrier for hydrogen-absorbing materials due to its excellent chemical stability and gas permeability. In this work, polysiloxane, water, and a emulsifier are ultrasonically injected into a uniform emulsion, and the hydrogen getter DEB-Pd/C (Palladium on carbon) is then added. Under the catalysis of platinum (Pt), the cross-linking agent undergoes a hydrosilylation reaction to cross-link polysiloxane in emulsion to form silicone rubber. Then, the water was removed by freeze-drying, and the loss of water constructed a porous frame structure for silicone rubber, thus obtaining porous silicone rubber. The difference in hydrogen absorption performance between porous silicone rubber and ordinary silicone rubber was compared. It was found that, with the increase in water in the emulsion, the porous frame of silicone rubber was gradually improved, and the hydrogen absorption performance was improved by 243.4% at the highest, almost reaching the theoretical saturated hydrogen absorption capacity. Porous silicone rubber was prepared by emulsion mixing, which provided a new idea for further improving the hydrogen absorption performance of silicone rubber.

The effect of milling time on formation of magnesium-activated carbon composites as hydrogen absorbing materials

Hydrogen is a potential environmentally friendly fuel, but it has problems in terms of storage. Hydrogen storage using magnesium (Mg) and activated carbon (AC) is an effective and safe alternative because it can store hydrogen in a large enough capacity. This research was conducted to study the potential of Mg-AC material with addition of cobalt as catalyst in storing hydrogen by studying the effect of milling time and weight ratio of Mg-AC on the characteristics of the composites and the amount of hydrogen gas that can be adsorbed. Composites were formed using mechanical milling method using Fritsch 6 Planetary Ball Mill. The prepared composites were characterized using the X-ray diffraction (XRD), Fourier Transform Infra-Red (FTIR), Scanning Electron Microscopy (SEM) and Thermal Gravimetric Analysis (TGA). XRD analysis showed that MgH2 compound was formed starting from 3 hr of milling time. The results of FTIR characterization showed that more C-H groups were formed with increasing milling time. The SEM graphs show that the longer milling time, the more evenly the distribution of particles in the Mg-AC composite and forming more nano particles. Meanwhile, the TGA analysis showed that with the addition of 5% AC, 10% and 15% then a weight reduction reached 9.6%, 10.6% and 14.2%, respectively.

Multicomponent Metal Hydride Materials for Hydrogen Energy Storage Systems

This paper presents the results of experimental studies of new hydrogen absorbing materials based on AB5 type alloys used for solid-phase hydrogen storage. The crystal structures, morphology, and hydrogen absorption properties of the new prepared samples were investigated. The effect of different metal additives on the properties of intermetallic compounds was studied

Raising the Dehydrogenation Rate of a Mg-CMC (Carboxymethylcellulose, Sodium Salt) Composite by Alloying Ni via Hydride-Forming Milling

In our previous work, samples with a composition of 95 wt% Mg + 5 wt% CMC (Carboxymethylcellulose, Sodium Salt, [C6H7O2(OH)x(C2H2O3Na)y]n) (named Mg-5 wt%CMC) were prepared through hydride-forming milling. Mg-5 wt%CMC had a very high hydrogenation rate but a low dehydrogenation rate. Addition of Ni to Mg is known to increase the hydrogenation and dehydrogenation rates of Mg. We chose Ni as an additive to increase the dehydrogenation rate of Mg-5 wt%CMC. In this study, samples with a composition of 90 wt% Mg + 5 wt% CMC + 5 wt% Ni (named Mg-5 wt%CMC-5 wt%Ni) were made through hydride-forming milling, and the hydrogenation and dehydrogenation properties of the prepared samples were investigated. The activation of Mg-5 wt%CMC-5 wt%Ni was completed at the 3rd hydrogenation-dehydrogenation cycle (N=3). Mg-5 wt%CMC-5 wt%Ni had an effective hydrogen-storage capacity (the quantity of hydrogen stored for 60 min) of 5.83 wt% at 593 K in 12 bar hydrogen at N=3. Mg-5 wt%CMC-5 wt%Ni released hydrogen of 2.73 wt% for 10 min and 4.61 wt% for 60 min at 593 K in 1.0 bar hydrogen at N=3. Mg-5 wt%CMC-5 wt%Ni dehydrogenated at N=4 contained Mg and small amounts of MgO, β-MgH2, Mg2Ni, and Ni. Hydride-forming milling of Mg with CMC and Ni and Mg2Ni formed during hydrogenation-dehydrogenation cycling are believed to have increased the dehydrogenation rate of Mg-5 wt%CMC. As far as we know, this study is the first in which a polymer CMC and Ni were added to Mg by hydride-forming milling to improve the hydrogenation and dehydrogenation properties of Mg. Key words: hydrogen absorbing materials, mechanical milling, scanning electron microscopy (SEM), X-ray diffraction, a polymer CMC (Carboxymethylcellulose, Sodium Salt) addition, Ni addition

Acceleration of hydrogen absorption by palladium through surface alloying with gold

Enhancement of hydrogen (H) absorption kinetics improves the performance of hydrogen-purifying membranes and hydrogen-storage materials, which is necessary for utilizing hydrogen as a carbon-free energy carrier. Pd-Au alloys are known to show higher hydrogen solubility than pure Pd. However, the effect of Au on the hydrogen penetration from the surface into the subsurface region has not been clarified so far. Here, we investigate the hydrogen absorption at Pd-Au surface alloys on Pd(110) by means of thermal desorption spectroscopy (TDS) and hydrogen depth profiling with nuclear reaction analysis (NRA). We demonstrate that alloying the Pd(110) surface with submonolayer amounts of Au dramatically accelerates the hydrogen absorption. The degree of acceleration shows a volcano-shaped form against Au coverage. This kinetic enhancement is explained by a reduced penetration barrier mainly caused by a destabilization of chemisorbed surface hydrogen, which is supported by density-functional-theory (DFT) calculations. The destabilization of chemisorbed surface hydrogen is attributed to the change of the surface electronic states as observed by angle-resolved photoemission spectroscopy (ARPES). If generalized, these discoveries may lead to improving and controlling the hydrogen transport across the surfaces of hydrogen-absorbing materials.

Hydrogen Storage Properties of Mg-Graphene Composites

To improve the hydrogen uptake and release properties of magnesium (Mg), five weight percent of graphene was added to pre-milled Mg by milling in hydrogen (reaction-involving milling). The hydrogen uptake and release properties of the graphene-added Mg (named Mg-5graphene) were investigated. Pre-milling of Mg (for 24 h) and then adding graphene by milling in hydrogen (for 30 min) significantly increased the hydrogen uptake and release rates and the quantities of hydrogen absorbed and released for 60 min of the Mg and graphene composite. The activation of Mg-5graphene was completed after the second hydrogen uptake-release cycle (n=2). Mg-5graphene had a high effective hydrogen-storage capacity (quantity of hydrogen absorbed for 60 min) of 5.47 wt% at 593 K in 12 bar H2 at n=3. Mg-5graphene absorbed 0.92 wt% H for 2.5 min, 2.67 wt% H for 10 min, and 5.62 wt% H for 60 min in 12 bar H2 and released 0.25 wt% H for 2.5 min and 4.99 wt% H for 60 min in 1.0 bar H2 at 623 K at n=1. The increase in ID/IG, the ratio of intensities of D and G peaks in Raman spectra, after reaction-involving milling of the pre-milled Mg with graphene, compared with that of the used graphene, suggests that defects and disordering in the graphene were increased. We believe that the generation of stacking fault disorder and formation of turbostratic graphite occurred after milling with the pre-milled Mg, rather than the formation of defects, in graphene. Key words: hydrogen absorbing materials, mechanical milling, hydrogen, microstructure, graphene-added Mg alloy

LaNi5 hydride powder flowability as a function of activation and hydrogen content

Volume expansion of hydrogen absorbing materials, together with inter-particle friction can cause tension accumulation in hydride containers during absorption. When hydride particles absorb hydrogen there is an important volume increase, in the order of 25%. Particles have to accommodate to the container geometry but this movement is opposed by inter-particle friction. Under certain conditions tensions can build up, compromising the mechanical integrity of the container. This phenomenon needs to be addressed at the design stage to avoid mechanical failure of the container.Flow behavior of powder materials is a relevant technological field, usually addressed by means of qualitative or quantitative flowability measuring devices. The rotating drum technique, while mainly qualitative, is well established and can be modified into a completely sealed unit. To determine the flowability of a hydride under different activation stages and hydrogen content levels we developed a rotating drum device that can be pressurized with hydrogen or depressurized. We report particle size evolution and flowability measurements of a hydrogen absorbing material (LaNi5) at different stages of activation for both absorbed and desorbed states. The results of the present study show that the flowability of LaNi5 in more dependent on the degree of activation of the sample than on hydrogen absorption state.

Dynamic Blocking by CO of Hydrogen Transport across Pd70Au30(110) Surfaces

CO adsorption affects hydrogen transport across surfaces of hydrogen-absorbing materials. On Pd70Au30(110), CO was found to block the desorption sites for absorbed hydrogen. However, the detailed CO adsorption site and hence the blocking mechanism have not been clarified yet. In this study, we investigated the CO adsorption structure on Pd70Au30(110) by using reflection–absorption infrared spectroscopy (RAIRS). We demonstrate that the CO adsorption structure depends on the CO coverage and sample temperature. We also performed thermal desorption spectroscopy (TDS) simulations on the basis of the RAIRS results and clarified the dynamical mechanism of the CO blocking where the CO site transfer from the Pd on-top to the Pd–Pd bridge sites enhances the blocking efficiency. These discoveries would lead to understanding and controlling the hydrogen transport across the Pd–Au alloy and Pd-related surfaces.

Hydrogen Absorption in Metal Thin Films and Heterostructures Investigated in Situ with Neutron and X-ray Scattering

Due to hydrogen possessing a relatively large neutron scattering length, hydrogen absorption and desorption behaviors in metal thin films can straightforwardly be investigated by neutron reflectometry. However, to further elucidate the chemical structure of the hydrogen absorbing materials, complementary techniques such as high resolution X-ray reflectometry and diffraction remain important too. Examples of work on such systems include Nb- and Pd-based multilayers, where Nb and Pd both have strong affinity to hydrogen. W/Nb and Fe/Nb multilayers were measured in situ with unpolarized and polarized neutron reflectometry under hydrogen gas charging conditions. The gas-pressure/hydrogen-concentration dependence, the hydrogen-induced macroscopic film swelling as well as the increase in crystal lattice plane distances of the films were determined. Ferromagnetic-Co/Pd multilayers were studied with polarized neutron reflectometry and in situ ferromagnetic resonance measurements to understand the effect of hydrogen absorption on the magnetic properties of the system. This electronic effect enables a novel approach for hydrogen sensing using a magnetic readout scheme.

In operando visualization of hydride-graphite composites during cyclic hydrogenation by high-resolution neutron imaging

Hydrogen solid-state storage in metal hydrides has attracted remarkable attention within the past decades due to their high volumetric storage densities at low operating pressures. In particular, recently emerged hydride-graphite composites (HGC) can enable a safe, reliable and very compact hydrogen storage solution for various applications. In this regard, only little is known about the activation behavior of such HGC, their cycle stability and degradation effects. Because of the high sensitivity to hydrogen, neutron imaging offers a distinctive approach to examine in operando reaction fronts, swelling effects and microstructural changes of hydrogen absorbing materials with high spatial and temporal resolution. In this contribution, a comprehensive analysis of various phenomena during activation and cycling of HGC based on a Ti–Mn hydrogen absorbing alloy and expanded natural graphite is reported for the first time. A neutron radiography and tomography set-up with a spatial resolution down to 7 μm was utilized allowing highest detection precision. During initial hydrogenation, regions with enhanced reactivity are observed which contradicts a theoretically expected homogeneous reactivity inside the HGC. These active regions grow with the number of hydrogenation-dehydrogenation cycles until the whole HGC volume uniformly participates in the hydrogen sorption reaction. With regard to long-term hydrogenation-dehydrogenation cycling, inhomogeneous swelling effects were observed from which essential conclusions for technical HGC-based tank systems can be derived.

Study of the thermodynamic properties of a hydrogen-absorbing alloy LaFe0.1Mn0.3Ni4.8 for systems for hydrogen storage and purification

The article is devoted to methodological problems of investigation of the pressure-concentration-temperature (PCT) phase diagrams of hydrogen-absorbing materials that are used in metal hydride systems for storage and purification of hydrogen based on intermetallic compounds of the AB5-type. The problem is discussed with an example of the PCT-diagram of the LaFe0.1Mn0.3Ni4.8 alloy, which is promising for creation of metal hydride systems for storage and purification of hydrogen integrated with power plants (with a power of up to 5 kW) based on fuel cells with a solid-polymer electrolyte.

Hydrogen storage system based on hydride materials incorporating a helical-coil heat exchanger

Metal hydrides offer the potential to store hydrogen at modest pressures and temperatures with high volumetric efficiencies. The process of charging hydrogen into a metal powder to form the hydride is exothermic. The heat released by the reaction must be removed quickly in order to maintain a rapid charging rate. An effective method for heat removal is to embed a heat exchanger within the metal hydride bed. Here, we investigate the effectiveness of a helical coil heat exchanger tube to remove the heat generated during the absorption process. This paper presents a three-dimensional mathematical model formulated in Ansys Fluent 12.1 to evaluate the transient heat and mass transfer in a cylindrical metal hydride tank embedded with a helical-coil cooling tube. We present results from a parametric study of hydrogen storage efficiency as a function of helical coil pitch and convective heat transfer coefficient (h) within the cooling tube. We also explore the effect of adding aluminum foam to enhance the thermal conductivity of the metal hydride. The parametric study reveals that the mass of stored hydrogen is less sensitive to the coil pitch when aluminum foam is added. It is also found that the absorption rate increases with h as expected, although the rate of improvement diminishes at high values of h. Results were examined at filling times of 3 and 6 min to draw conclusions about the overall effectiveness of this hydrogen storage system. At 3 min, it is found that the addition of 5% Al foam is optimal, and h = 1000 W/m2-K is sufficient to bring the metal hydride to saturation; under these conditions a non-dimensional pitch of 0.5 maximizes the hydrogen absorption. Adding Al foam beyond 5% does not improve volumetric efficiency as the Al foam begins to displace the active hydrogen-absorbing material.

The method of limited volume electrodes as a tool for hydrogen electrosorption studies in palladium and its alloys

The review summarizes selected aspects of the electrochemical investigations on hydrogen absorption in palladium and its alloys prepared as thin layers deposited on a conductive substrate. These kinds of electrodes are named “limited volume electrodes” (LVEs). We demonstrate that LVE methodology creates new possibilities for electrochemical studies on hydrogen-absorbing materials. In this paper, we describe the procedures of preparation and characterization of Pd-based LVEs and give a survey of the investigations on hydrogen electrosorption performed with the use of LVEs. We discuss the influence of such factors as electrode potential, temperature, electrolyte composition, electrode thickness, and other experimental conditions on the process of hydrogen and deuterium absorption in Pd LVEs. The results concerning Pd alloys are thoroughly reviewed. The studies on thermodynamics, kinetics, and mechanism of hydrogen electrosorption in Pd and its alloys are also summarized. Attention is paid to the examination of the interrelation between hydrogen absorption and other electrochemical processes taking place on LVEs. Finally, possible applications of the LVE methodology in the context of electrochemical power sources are mentioned.

Non-harmonic electro-chemical and pneumato-chemical impedance spectroscopies for analyzing the hydriding kinetics of palladium

Analysis of phase transformation processes observed in most hydrogen-absorbing materials (pure metals, alloys or compounds) is still a matter of active research, in view of electrochemical or chemical hydrogen storage applications. Most metal hydride systems present a large and irreducible hysteresis, indicating that non-linear phenomena are taking place during hydrogen sorption/desorption reactions. Investigation of hydriding kinetics therefore requires non-harmonic spectroscopies to fulfill the requirements of linearity and time invariance imposed by the theory of systems. The purpose of this paper is to report on the insertion of atomic hydrogen into a palladium foil. The process is analyzed using electrochemical (the electrolyte is the source of hydrogen) and pneumato-chemical (the gas phase is the source of hydrogen) experimental spectroscopies. Pneumato-chemical impedance spectroscopy (PIS) provides additional information to electro-chemical impedance spectroscopy (EIS) since (i) there is no electrolyte and no electrified interface; (ii) experiments can be performed over long periods of time, without any pollution (closed systems); (iii) there is no parasite reaction such as hydrogen evolution encountered in electrochemical experiments; (iv) the temperature range of investigation is larger; (v) there is no kinetic limitations on the electrolyte side of the interface. Results obtained in single and two-phase domains of the model PdH system, using both EIS and PIS spectroscopies, are reported and discussed. Surface and bulk microscopic rate parameters are compared.

Hydrogen Electrosorption into Pd−Cd Nanostructures

Hydrogen-absorbing materials are crucial for both the purification and storage of hydrogen. Pd and Pd-based alloys have been studied extensively for their use as both hydrogen dissociation catalysts and hydrogen selective membrane materials. It is known that incorporating metal atoms of different sizes into the Pd lattice has a major impact on the hydrogen absorption process. In this paper, hydrogen electrosorption into nanostructured Pd-Cd alloys has been studied for different compositions of Cd that varied from 0 to 15 at. %. The low cost of Cd makes it an attractive material to combine with Pd for hydrogen sorption. A combination of chronoamperometry and cyclic voltammetric experiments was used to determine the ratio of the H/(Pd + Cd) and the kinetics of hydrogen sorption into these Pd-Cd alloys at different potentials. It was found that the maximum H/(Pd + Cd) value was 0.66 for pure Pd, and this decreased with increasing the amount of Cd. Also, the alpha (solid solution) to beta phase (metal hydride) hydrogen transition was determined to be the slowest step in the absorption process and was practically eliminated when an optimum amount of Cd atoms was doped (i.e., Pd-Cd(15%)). With increasing the amount of Cd, more hydrogen was absorbed into the Pd-Cd nanostructures at the higher potentials (the alpha phase region). The faster kinetics, along with the decrease in the phase transition of hydrogen sorption into the Pd-Cd nanostructures when compared to pure Pd, makes the Pd-Cd nanostructures attractive for use as a hydrogen dissociation catalytic capping layer for other metal hydrides or as a hydrogen selective membrane.

Nanogravimetric Evaluation of Hydrogen Uptake in Thin Film Materials by A Quartz Crystal Microbalance

AbstractTo study the hydrogen storage materials in their thin film format provides a unique approach to investigate many interfacial phenomena associated with current research on hydrogen storage materials. However, the challenge is to establish a reliable method to measure weight change of at least a few tens of nanograms in pressurized hydrogen gas. We demonstrate the application of a quartz crystal microbalance for direct mass-metric evaluation of hydrogen storage materials in the pressure range of 0˜40 bars. The frequency shift of a quartz crystal coated with hydrogen absorbing materials is affected by the hydrogen mass uptake on the crystal, the pressure and the viscosity of the gases, and the crystal surface roughness, of which the roughness contribution has no direct analytical expression. Through a control experiment on the same crystal in helium, the roughness contribution in hydrogen can be derived and the frequency shift due to the hydrogen mass uptake is obtained.

Fourier-Domain Analysis of Hydriding Kinetics Using Pneumato-Chemical Impedance Spectroscopy

Analysis of phase transformation processes observed in hydrogen absorbing materials (pure metals, alloys, or compounds) is still a matter of active research. Using pneumato-chemical impedance spectroscopy (PIS), it is now possible to analyze the mechanism of hydriding reactions induced by the gas phase. Experimental impedance diagrams, measured on activated LaNi5 in single- and two-phase domains, are reported in this paper. It is shown that their shape is mostly affected by the slope of the isotherm at the measurement point. By considering the details of the multistep reaction paths involved in the hydriding reaction, model impedance equations have been derived for single- and two-phase domains, and fitted to experimental impedance diagrams. The possibility of separately measuring surface and phase transformation resistances, hydrogen diffusion coefficient, and hydrogen solubility in each composition domain is discussed.

Direct mass determination of hydrogen uptake using a quartz crystal microbalance

The authors demonstrate the application of a quartz crystal microbalance for direct mass determination of hydrogen uptake in storage materials in the pressure range of 0–40bars. The frequency shift of a quartz crystal coated with hydrogen absorbing materials is affected by the hydrogen mass uptake on the crystal, the pressure and the viscosity of the gases, and the crystal surface roughness, of which the roughness contribution has no analytical expression. Through a control experiment on the same crystal in helium, the roughness contribution in hydrogen can be derived and the frequency shift due to the hydrogen mass uptake can be obtained.

Ultrasonic studies of hydrogen absorbing materials: Quasicrystals, nanocrystals, and intermetallic compounds

Resonant ultrasound spectroscopy was used to study several materials—nanocrystalline palladium, quasicrystalline Ti‐Zr‐Ni, and a number of intermetallic compounds—that have the ability to absorb considerable amount of hydrogen, and thus are of potential use for hydrogen storage. Elastic energies are relevant to the thermodynamics of such systems, which are often described by a lattice gas model. Elastic interactions between dissolved H atoms lead to a critical temperature and precipitation of a hydride phase below the critical temperature. The energetics of hydride precipitation depend on the elastic constants. Thus, it is important that the elastic properties of such systems be measured. In addition, these materials are of interest for several other reasons. The elastic constants and internal friction for the hydrogen‐free materials were measured over a temperature range of 3 to 300 K, and in a few cases to higher temperatures. These results will be discussed and interpreted. [This work was supported by the U.S. National Science Foundation under Grant DMR‐0070808.]

06/01571 Review on hydrogen absorbing materials — structure, microstructure, and thermodynamic properties: Bououdina, M. et al. International Journal of Hydrogen Energy, 2006, 31, (2), 177–182

06/01571 Review on hydrogen absorbing materials — structure, microstructure, and thermodynamic properties: Bououdina, M. et al. International Journal of Hydrogen Energy, 2006, 31, (2), 177–182