Hydride System Research Articles

Numerical analysis of constructive and regime parameter effects on the efficiency of metal hydride systems for hydrogen purification

This work used a numerical method to study the influence of such parameters as inlet pressure in the system, thermal conductivity of the bed, cooling conditions of the reactor and its geometric characteristics on the efficiency of a metal hydride hydrogen purification system. The criterion chosen for the efficiency of the hydrogen purification system was the alloy fraction saturated with hydrogen at the time when the hydrogen breaks through the metal hydride bed, the hydrogen mole fraction at the outlet rises to 3% and the losses increase.

Superior Kinetic and Cyclic Performance of a 2D Titanium Carbide Incorporated 2LiH + MgB2 Composite toward Highly Reversible Hydrogen Storage

Reactive hydride system of 2LiH + MgB2/2LiBH4 + MgH2 is of great potential as hydrogen storage material due to its high theoretical hydrogen storage capacity. However, it suffers from sluggish dehy...

Mercury Contamination in Water and Sediments and the Associated Health Risk: A Case Study of Artisanal Gold-mining

This study investigated mercury (Hg) contamination in the Gilgit-Baltistan, Pakistan. Water and sediment samples were collected from various sites having artisanal gold-mining along the Indus, Gilgit, and Hunza Rivers. Sediments were classified as wet sediment (WS, collected just after amalgamation), fresh dry sediment (FDS, collected after 1–2 h of amalgamation), and old dried sediment (ODS, collected after 1–2 days of amalgamation). Samples were analyzed for Hg by atomic absorption spectrophotometry with a mercury hydride system. Mercury mean concentrations were 2767 mg/kg in WS, 1917 mg/kg in FDS, and 191 mg/kg in ODS. These results revealed very high levels of Hg contamination in the WS and FDS. The Hg contamination of the spring (drinking water) did not exceed the permissible limits set by the World Health Organization (WHO) and Pakistan’s environmental protection agency (Pak-EPA); however, the stream water surpassed these limits. Therefore, the Hg levels in the drinking water was used to assess the potential human health risk via the average daily dose (ADD) and hazard quotient (HQ). The ADD values were 0.03 and 0.06 µg/kg-day and HQ value of 0.9 and 2.0 for adults and children, respectively. This level of Hg contamination level is alarming and could be hazardous in future.

High-temperature superconductivity in sulfur hydride evidenced by alternating-current magnetic susceptibility.

ABSTRACTThe search for high-temperature superconductivity is one of the research frontiers in physics. In the sulfur hydride system, an extremely high Tc (∼200 K) has been recently developed at pressure. However, the Meissner effect measurement above megabar pressures is still a great challenge. Here, we report the superconductivity identification of sulfur hydride at pressure, employing an in situ alternating-current magnetic susceptibility technique. We determine the superconducting phase diagram, finding that superconductivity suddenly appears at 117 GPa and Tc reaches 183 K at 149 GPa before decreasing monotonically with increasing pressure. By means of theoretical calculations, we elucidate the variation of Tc in the low-pressure region in terms of the changing stoichiometry of sulfur hydride and the further decrease in Tc owing to a drop in the electron–phonon interaction parameter λ. This work provides a new insight into clarifying superconducting phenomena and anchoring the superconducting phase diagram in the hydrides.

Electrocatalysis of Ketjenblack-Supported Ru-Ir Cathode for the Electrohydrogenation of Toluene to Methylcyclohexane in the Organic Hydride System

Hydrogenation of toluene (TL) and dehydrogenation of methylcyclohexane (MCH) has been paid great attention for a highly efficient H2 storage technology [1,2]. At energy supply area, TL is hydrogenated to MCH by the catalytic hydrogenation using H2 produced by the water-electrolysis. We can easily transport and store MCH using the current infrastructures, because MCH is a component of petroleum and liquid state at ambient conditions. At energy demanding area, the catalytic dehydrogenation of MCH to TL and H2 (47.4 kg-H2/m3-MCH) is conducted. H2 can be used as an energy source, and TL is reused as the H2 carrier, repeatedly. To improve the H2 storage system to more efficient one, a direct electrohydrogenation of TL with water using a solid polymer electrolyte (SPE) electrolysis cell and 50 wt% Pt/Ketjenblack (KB) cathode has been proposed (Fig. 1) [3]. In those system, water is oxidized at the anode, and TL is electrochemically reduced to MCH at the cathode; however, the high loading of Pt is disadvantage from the viewpoints of system cost. For the efficient hydrogenation of TL, it is essential to reduce Pt or other precious metal loadings with keeping suppression of the competitive H2 evolution. In this study, we found that Ru-Ir alloy supported on KB (Ru-Ir/KB) electrocatalyst showed superior electrocatalytic activity for the electrohydrogenation of TL to MCH under galvanostatic electrolysis conditions at 0.20 A cm-2. 5 wt% Ru-5 wt% Ir/KB loaded on a gas-diffusion layer (GDL) cathode (0.2 mgRu-Ir cm-2) showed a higher faradic efficiency of MCH formation than the 50 wt% Pt/KB loaded on the GDL cathode (1.0 mgPt cm-2), though the working potential of -0.183 V (SHE) at the former was slightly negative than that of -0.071 V (SHE) at the later. This indicated the significant reduction of amount of precious metals used for the electrohydrogenation of TL. Characterization studies for the Ru-Ir/KB electrocatalyst were conducted by using X-ray diffraction (XRD), transmission electron microscopy with energy dispersive spectroscopy (TEM-EDS) and X-ray absorption fine structure spectroscopy (XAFS), and a formation of hcp-structured Ru-Ir alloy was revealed. Based on the electrochemical and kinetic studies, synergy mechanisms of Ru and Ir for the electrohydrogenation of TL were proposed. To be concrete, a fast hydrogenation of TL to MCH on the Ru site, a fast electrocatalytic reduction of H+ to H-species on the Ir site, and a fast spillover of H-species from Ir to Ru, these three steps cooperate.

Conceptual Design of Yttrium Oxyhydrides: Phase Diagram, Structure, and Properties

The synthesis of stable yttrium oxyhydride-type compounds raised a principal question regarding the key factors that may be responsible for formation routes and structural features of these attractive materials. For solving this challenge, the interplay between chemical composition and crystalline architectures has been theoretically explored via modeling structural transformations caused by the gradual oxidation of the host metal hydride system. The close combination of group-theory methods, mixed-anion chemistry arguments, and relevant density functional theory calculations provided us with the opportunity to suggest and characterize the candidate models for most probable stoichiometric versions of yttrium oxyhydrides. The predicted chemical compositions along with the crystallization results have been summarized in the phase diagram. It is shown that the cation–ligand interaction governs the structural stability which is achieved by matching favorable crystallographic positions of the oxygen and hydrog...

Hydrogen storage properties of TiFe-based ternary mechanical alloys with cobalt and niobium. A thermochemical approach

Ternary alloys of general composition (TiFe)100-xMx (M = Co, Nb) have been synthesized from pure metals through high-energy ball milling. The maximum concentration of alloying components allowing formation of single phase TiFe-type compounds has been defined as 2 at.%. The hydrogenation behavior of the mechanical alloys in comparison with the arc-melted ones of the same composition has been studied by a combination of volumetric and calorimetric techniques. Influence of the alloy composition and the synthesis mode on the crystal structure of TiFe and its hydrides has been evaluated. It has been shown that the thermochemical method based on calorimetric titration provides more accurate information about phase transformations in the nanocrystalline metal hydride systems. The obtained results show that the third components slightly affect the hydrogen storage performance of non-equilibrium mechanical alloys in contrast with alloys produced by conventional melting.

Morphology-Dependent Stability of Complex Metal Hydrides and Their Intermediates Using First-Principles Calculations.

Complex light metal hydrides are promising candidates for efficient, compact solid-state hydrogen storage. (De)hydrogenation of these materials often proceeds via multiple reaction intermediates, the energetics of which determine reversibility and kinetics. At the solid-state reaction front, molecular-level chemistry eventually drives the formation of bulk product phases. Therefore, a better understanding of realistic (de)hydrogenation behavior requires considering possible reaction products along all stages of morphological evolution, from molecular to bulk crystalline. Here, we use first-principles calculations to explore the interplay between intermediate morphology and reaction pathways. Employing representative complex metal hydride systems, we investigate the relative energetics of three distinct morphological stages that can be expressed by intermediates during solid-state reactions: i) dispersed molecules; ii) clustered molecular chains; and iii) condensed-phase crystals. Our results verify that the effective reaction energy landscape strongly depends on the morphological features and associated chemical environment, offering a possible explanation for observed discrepancies between X-ray diffraction and nuclear magnetic resonance measurements. Our theoretical understanding also provides physical and chemical insight into phase nucleation kinetics upon (de)hydrogenation of complex metal hydrides.

A new mutually destabilized reactive hydride system: LiBH4–Mg2NiH4

Abstract In this work, the hydrogen sorption properties of the LiBH4–Mg2NiH4 composite system with the molar ratio 2:2.5 were thoroughly investigated as a function of the applied temperature and hydrogen pressure. To the best of our knowledge, it has been possible to prove experimentally the mutual destabilization between LiBH4 and Mg2NiH4. A detailed account of the kinetic and thermodynamic features of the dehydrogenation process is reported here.

Synergy of Ru and Ir in the Electrohydrogenation of Toluene to Methylcyclohexane on a Ketjenblack-Supported Ru-Ir Alloy Cathode

An organic hydride system based on hydrogenation/dehydrogenation of toluene (TL)/methylcyclohexane (MCH) has been studied as a hydrogen storage technology. Electrohydrogenation of TL to MCH using a proton exchange membrane (PEM) electrolyzer is proposed as a candidate for the hydrogenation of TL in the organic hydride system. Recently, we reported that a Ketjenblack-supported Ru-Ir alloy (Ru-Ir/KB) cathode was effective for the reaction; however, electrohydrogenation mechanisms and catalyses of Ru and Ir in the electrohydrogenation have been unclear. In this paper, detailed characterization studies using transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), and electrochemical studies using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) for hydrogen evolution and kinetic studies for catalytic hydrogenation of TL by Ru-Ir/KB catalysts were conducted. On the ...

(IBA Technology Award) Energy Storage Batteries using Mn and Ti Based Elelctrode Materials

Renewable generation, such as solar and wind, is intermittent, which causes sudden and unanticipated changes to power output and contributes to electricity grid instability. The stability and reliability of electricity grids requires a continuous balance between energy supply and demand. The aqueous lithium-ion battery (LIB) may solve both the safety problem associated with lithium-ion batteries that use highly toxic and flammable organic solvents, and the poor cycling life associated with commercialized aqueous rechargeable batteries including lead-acid and nickel-metal hydride systems. Aqueous LIBs have been demonstrated to be one of the most promising stationary power sources for the sustainable energy such as wind and solar power. As early as in 2005, we developed a new concept hybrid electrochemical supercapacitor in which a Li-ion intercalated compound was used as a positive electrode in combination with an activated carbon negative electrode in a Li2SO4 aqueous electrolyte (ZL. 200510025269.6). A hybrid cell consisting of a spinel LiMn2O4 positive and an AC negative electrode shows excellent reversibility with a sloping voltage profile from 0.8 to 1.8 V at an average voltage near 1.3 V, and delivers an 8 Wh/kg of 60000 F practical cell. In order to improve the specific energy, we employed LiTi2(PO4)3, but the cell shows poorer cycling stability compared with the pure AC anode. We found that, in the presence of oxygen, the discharged state of lithium-ion intercalated compounds (LIC) of all negative electrode materials will react with water and O2 despite of the pH value of the electrolyte, which is mainly responsible for the capacity fading of aqueous lithium-ion batteries during charge/discharge cycling. By eliminating the O2 (using a sealed cell), adjusting the pH values of the electrolyte, and using carbon-coated electrode materials; the LIB shows much cycling stability. A commercialized hybrid LIB shows a specific energy of ca. 30 Wh/kg, and exhibits a good cycling stability over 3500 cycles. In 2005, we also for the first time employed carbon coating technology to improve the electrode performance of Li4Ti5O4. By optimizing the graphitization and the coated carbon layer thickness, the nano-thickness carbon layer coated LTO shows excellent rate capability and less gas generation during cycling and storage. A LMO/LTO Li-ion battery show excellent cycling stability, high power and safety as stationary power source for smart-grid systems.

Parametric Studies on LaNi4.7Al0.3 based Hydrogen Storage Reactor with Embedded Cooling Tubes

Abstract This study reports the investigative conclusions of parametric studies conducted to understand the effect of operating parameters on absorption and desorption characteristics of LaNi4.7Al0.3 metal hydride system for thermal management applications. Reactor with improved design containing 55 embedded cooling tubes is fabricated and filled with 4 kg of metal hydride alloy. Using water as heat transfer fluid (HTF), effects of supply pressure, HTF temperature and HTF flow rate on absorption and desorption characteristics of the reactor are analyzed. Increasing supply pressure leads to prominent improvement in absorption capacity while the increase in HTF temperature enhanced desorption performance. At 20 bar and 20 °C, 46.2877 g of hydrogen (1.16 wt%) was absorbed resulting in total energy output of 707.3 kJ for 300 s. During desorption at 80 °C with water flow rate of 8 lpm, heat input of 608.1 kJ for 300 s resulted in 28.5259 g of hydrogen desorption.

A Simple Palladium Hydride Embedded Atom Method Potential for Hydrogen Energy Applications

When hydrogen is produced from a biomass or coal gasifier, it is necessary to purify it from syngas streams containing components such as CO, CO2, N2, CH4, and other products. Therefore, a challenge related to hydrogen purification is the development of hydrogen-selective membranes that can operate at elevated temperatures and pressures, provide high fluxes, long operational lifetime, and resistance to poisoning while still maintaining reasonable cost. Palladium-based membranes have been shown to be well suited for these types of high-temperature applications and have been widely utilized for hydrogen separation. Palladium's unique ability to absorb a large quantity of hydrogen can also be applied in various clean energy technologies, like hydrogen fuel cells. In this paper, a fully analytical interatomic embedded atom method (EAM) potential for the Pd-H system has been developed, that is easily extendable to ternary Palladium-based hydride systems, such as Pd-Cu-H and Pd-Ag-H. The new potential has fewer fitting parameters than previously developed EAM Pd-H potentials and is able to accurately predict the cohesive energy, lattice constant, bulk modulus, elastic constants, melting temperature, and the stable Pd-H structures in molecular dynamics (MD) simulations with various hydrogen concentrations. The EAM potential also well predicts the miscibility gap, the segregation of the palladium hydride system into dilute (α), and concentrated (β) phases.

A study on hydrogen absorption and dissolution in liquid lithium

Methods that plan to recover tritium from liquid lithium require intimate knowledge of the surface, sub-surface, and bulk chemistry associated with the interactions between hydrogen isotopes and lithium particles. Focusing on the lithium–lithium hydride system, previous studies have been able to determine concentrations associated with the liquidus curve, which separates the hydrogen dissolved in solution (known as the phase) from the hydrogen which precipitates out as lithium hydride (known as the phase). Knowledge of how these phases coexist in bulk melts is particularly important when the lithium is exposed to a hydrogen, deuterium, or tritium plasma, because they govern how quickly one can recover these isotopes in back-end processes for future lithium-walled fusion reactors. To this end, lithium samples were exposed to hydrogen plasmas in the Tungsten Fuzz Characterization of Nanofeatures (TUFCON) chamber at the University of Illinois. Each lithium sample was varied with respect to sample temperature, applied electrical bias, and length of sample exposure, and in each there coexisted a combination of the and phases. In all cases, two distinct absorption periods were observed during exposure. Similarly, two distinct desorption periods were observed during temperature-programmed desorption (TPD) scans. While similar desorption periods have been observed in the literature, changes in sample resistivity measured in the current study help to validate this behavior from a novel, condensed-phase perspective. The results of lithium exposures in TUFCON will be presented, along with a discussion on how the exposure conditions and phases affect recovery. Observations of superficial surface layers, and how they affect absorption and desorption, will be included in these discussions. How these results, along with the resultant marginally-enhanced dissolution behavior, can extend to tritium recycling efforts will also be explored.

Low-temperature selective catalytic dehydrogenation of methylcyclohexane by surface protonics.

The methylcyclohexane (MCH)–toluene cycle is a promising liquid organic hydride system as a hydrogen carrier. Generally, MCH dehydrogenation has been conducted over Pt-supported catalysts, for which it requires temperatures higher than 623 K because of its endothermic nature. For this study, an electric field was applied to Pt/TiO2 catalyst to promote MCH dehydrogenation at low temperatures. Selective dehydrogenation was achieved with the electric field application exceeding thermodynamic equilibrium, even at 423 K. With the electric field, “inverse” kinetic isotope effect (KIE) was observed by accelerated proton collision with MCH on the Pt/TiO2 catalyst. Moreover, Pt/TiO2 catalyst showed no methane by-production and less coke formation during MCH dehydrogenation. DRIFTS and XPS measurements revealed that electron donation from TiO2 to Pt weakened the interaction between catalyst surface and π-coordination of toluene. Results show that the electric field facilitated MCH dehydrogenation without methane and coke by-production over Pt/TiO2 catalyst.

Adiabatic magnesium hydride system for hydrogen storage based on thermochemical heat storage: Numerical analysis of the dehydrogenation

With hydrogen becoming more and more important as storage and carrier for renewable energy, there is an increasing need for flexible and efficient storage technologies. However, existing technologies, such as liquefaction or compression, often require a significant share of the hydrogens lower heating value. High-temperature metal hydrides (HT-MHs), such as magnesium hydride, are a promising alternative. Due to high operation temperatures, their application is challenging. A novel adiabatic hydrogen storage reactor based on the combination of a HT-MH with a thermochemical energy storage system (TCSS), such as Mg(OH)2/MgO + H2O, can be a solution. In this work, the previously published numerical simulations for hydrogen absorption are extended to the desorption process. A two-dimensional model for the hydrogen release was set up. The performance of the storage reactor is strongly dependent on the thermodynamic equilibrium of the reactions involved and less dependent on the reaction kinetics. Dehydrogenation is possible within 132 min, which is in the vicinity of the hydrogenation time. To enhance the dehydrogenation process, the water vapor pressure can be adjusted aiming for higher temperatures during the MgO hydration. Hydrogen can either be provided at constant pressure or constant mass flow rate.

Assessment of discrete breathers in the metallic hydrides

Computational assessment of the discrete breathers (also known as intrinsic localised modes) is performed in nickel and palladium hydrides with an even stoichiometry by means of molecular dynamics simulations. The breathers consisting of hydrogen and metallic atoms were excited following the experience obtained earlier by modelling the breathers in pure metallic systems. Stable breathers were only found in the nickel hydride system and only for the hydrogen atoms oscillating along 〈1 0 0〉 and 〈1 1 1〉 polarization axes. At this, two types of the stable breathers involving single oscillating hydrogen and a pair of hydrogen atoms beating in antiphase mode were discovered. Analysis of the breather characteristics reveals that its frequency is located in the phonon gap or lying in the optical phonon band of phonon spectrum near the upper boundary. Analysis of the movement of atoms constituting the breather was performed to understand the mechanism that enables the breather stabilization and long-term oscillation without dissipation its energy to the surrounding atoms. It has been demonstrated that, while in palladium hydride, the dissipation of the intrinsic breather energy due to hydrogen-hydrogen attractive interaction occurs, the stable oscillation in the nickel hydride system is ensured by the negligibly weak hydrogen-hydrogen interaction acting within a distance of the breather oscillation amplitude. Thus, our analysis provides an explanation for the existence of the long-living stable breathers in metallic hydride systems. Finally, the high energy oscillating states of hydrogen atoms have been observed for the NiH and PdH lattices at finite temperatures which can be interpreted as a fingerprint of the finite-temperature analogues of the discrete breathers.

Metal hydride reactor for dual use: Hydrogen storage and cold production

In case a metal hydride system is used for gaseous hydrogen storage application, the overall efficiency of the storage system can be significantly improved when the corresponding cooling or heating effect is additionally integrated into the application. In this study, it is analyzed how the efficiency of the gaseous hydrogen storage as well as the temperature level of the cold production can be adjusted using a simple, modular, air-cooled metal hydride reactor. For the study, a Hydralloy C5-graphite composite has been selected as reference material, and as geometry a simple tubular shape has been considered. In the first part of the manuscript, an analytical approach is presented analyzing the three different regimes in which a metal hydride reactor can be operated: to store hydrogen (Regime I), produce cold (Regime III), or to couple both options as “dual use” (Regime II), depending on the mass flow rates of hydrogen and air. In the second part of the manuscript, results of a detailed numerical study are presented and evaluated with respect to the outlet air temperature and the hydrogen utilization factor of the hydride reactor. It is shown that in Regime I, a high utilization factor and in Regime III, low outlet air temperature levels can be reached. Furthermore, in the “dual use” regime, the reactor can produce a cooling effect at different temperature levels and still show a high hydrogen utilization factor. In the last part of the manuscript, the effects of a modular reactor system as well as the operation of the reactor in pressure control mode are discussed to extend the basic description of the problem.

A simple embedded atom potential for Pd-H alloys

ABSTRACTMetal Hydride systems are an important research topic in material science because of their many practical, industrial, and scientific applications. Therefore, the development of reliable and efficient interatomic potentials for metal hydrides systems, to be utilised in molecular simulations, can be of great value in accelerating the research in this field. In this paper, a fully analytical interatomic Embedded Atom Potential (EAM) for the Pd-H system has been developed, that can be easily extended to ternary Palladium-based hydride systems. The new potential has fewer fitting parameters than previously developed EAM Pd-H potentials and can better predict the cohesive energy, lattice constant, bulk modulus, elastic constants, and the stable alloy crystal structures during molecular dynamics (MD) simulations for various hydrogen concentrations. The EAM potential also predicts the miscibility gap, the separation of a Pd-H system to dilute (α) and concentrated (β) phases.

Dehydrogenation properties of the LiNH2BH3/MgH2 and LiNH2BH3/LiBH4 bi-component hydride systems for hydrogen storage applications

Lithium amidoborane (LiAB) is known as an efficient hydrogen storage material. The dehydrogenation reaction of LiAB was studied employing temperature-programmed desorption methods at varying temperature and H2 pressure. As the dehydrogenation products are in amorphous form, the XRD technique is not useful for their identification. The two-step decomposition temperatures (74 and 118 °C) were found to hardly change in the 1–80 bar pressure range. This is related either to kinetic effects or to thermal dependence of the reaction enthalpy. Further, the possible joint decomposition of LiNH2BH3 with LiBH4 or MgH2 was investigated. Indeed LiBH4 proved to destabilize LiAB, producing a 10 °C decrease of the first-step decomposition temperature, whereas no significant effect was observed by the addition of MgH2. The 5LiNH2BH3 + LiBH4 assemblage shows improved hydrogen storage properties with respect to pure lithium amidoborane.