Equilibrium Hydrogen Research Articles

Improvement of hydrogen storage properties of the AB 2 Laves phase alloys for automotive application

Hydrogen storage properties of the Ti 1.1CrMn AB 2-type Laves phase alloys, for both low (−30 °C) and high (80 °C) temperature applications, are improved by substituting Zr at Ti site. In agreement with the larger radius of Zr than Ti, the lattice volume of (Ti 1− x Zr x ) 1.1CrMn ( x=0, 0.05, 0.06 and 0.1) alloys, prepared by arc melting, increases with x. The increase in the Zr content leads to a decrease in the equilibrium hydrogen sorption pressure plateau and faster absorption kinetics, associated with an increase in the hydrogen storage capacity from 1.9 to 2.2 wt% for Ti 1.1CrMn and (Ti 0.9Zr 0.1) 1.1CrMn alloys, respectively. At −5 °C, (Ti 0.9Zr 0.1) 1.1CrMn alloy reversibly absorbs and desorbs 2.2 wt% at 160 bar within 250 s. Based on thermodynamic calculated values, the optimized Zr substituted alloy (Ti 0.9Zr 0.1) 1.1CrMn desorbs hydrogen at 3.2 bar at −30 °C and 135 bar at 80 °C. This is a significant reduction of the sorption pressure plateau as compared with the current technology for mobile applications based on Ti 1.1CrMn alloy with hydrogen desorption plateau above 400 bar at 80 °C. Finally, the mechanism of improved hydrogen storage properties is discussed based on the radius and the hydrogen affinity of the substituting element.

Properties of hydrogen absorption by nano-structured FeTi alloys

Abstract In this study, two different nano-structured samples of the FeTi compound were prepared by mechanical alloying and mechanical grinding. For these samples, kinetics of the initial rate of hydrogen absorption, and the equilibrium hydrogen pressure as a function of hydrogen concentration were measured. Mechanical alloying of Fe and Ti atoms produced the FeTi compound powder samples with microstructures of a mixture of nano-structured FeTi grains and amorphous phases. This sample exhibited a high initial rate of hydrogen absorption even at 298 K, however, a strongly reduced hydrogen storage capacity. Mechanical grinding of the FeTi produced samples of particles with a particular microstructure: surface layers with a mixture of nano-structured FeTi grains and amorphous phases, and a single crystalline phase of FeTi below the surface layers for each particle. This sample exhibited a high initial rate of hydrogen absorption without a significant reduction of the hydrogen storage capacity compared with that of the standard FeTi sample. This mechanical grinding treatment was found to be an effective method of surface modification to improve the initial activation of the FeTi hydrogen storage alloy.

Thermodynamic analysis of hydrogen production via autothermal steam reforming of selected components of aqueous bio-oil fraction

From a technical and economic point of view, autothermal steam reforming offers many advantages, as it minimizes heat load demand in the reformer. Bio-oil, the liquid product of biomass pyrolysis, can be effectively converted to a hydrogen-rich stream. Autothermal steam reforming of selected compounds of bio-oil was investigated using thermodynamic analysis. Equilibrium calculations employing Gibbs free energy minimization were performed for acetic acid, acetone and ethylene glycol in a broad range of temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm) values. The optimal O 2/fuel ratio to achieve thermoneutral conditions was calculated under all operating conditions. Hydrogen-rich gas is produced at temperatures higher than 700 K with the maximum yield attained at 900 K. The ratio of steam to fuel and the pressure determine to a great extent the equilibrium hydrogen concentration. The heat demand of the reformer, as expressed by the required amount of oxygen, varies with temperature, steam to fuel ratio and pressure, as well as the type of oxygenate compound used. When the required oxygen enters the system at the reforming temperature, autothermal steam reforming results in hydrogen yield around 20% lower than the yield by steam reforming because part of the organic feed is consumed in the combustion reaction. Autothermicity was also calculated for the whole cycle, including preheating of the organic feed to the reactor temperature and the reforming reaction itself. The oxygen demand in such a case is much higher, while the amount of hydrogen produced is drastically reduced.

Equilibrium shift in membrane reactors: A thermodynamic analysis of the dehydrogenative conversion of alkanes

The shift in equilibrium conversion for dehydrogenation and dehydroalkylation reactions as a result of selective extraction of hydrogen in a membrane reactor has been evaluated by a simple model based on thermodynamics taking into account chemical reaction equilibrium and hydrogen equilibrium across a 100% hydrogen-selective membrane. There is a limit to which the equilibrium can be shifted in a membrane reactor, depending on the thermodynamics of given reactions. The effects of temperature, pressure and sweep gas flow rate on equilibrium conversion and selectivity in a membrane reactor have been demonstrated.

Disproportionation Characteristics of a Zirconium-Cobalt Hydride Bed under ITER Operating Conditions

Quantitative assessment of a disproportionation in the ZrCo-hydrogen system under ITER-relevant operating conditions was performed by means of experimental tests and a theoretical calculation. In the static temperature experiments with equilibrium hydrogen pressures, a 10% disproportionation of ZrCoHx (x = 2.0 and 2.5) was observed in 5.5 h at 415° (~78 kPa), 9 h at 400° (~72 kPa), 172 h at 380° (~51 kPa), and 1626 h at 350° (~28 kPa). An experimental formula [log τ = 17 268/T (K) - 25.814, where τ is the reaction time (day) of 10% disproportionation] was derived from these experiments. Experiments with a temperature cycling of up to 125 cycles (from room temperature to 350 to 360°) proved that no enhancement of a disproportionation occurs in the ZrCoHx (1.7 < x ≤ 2.0). Typical operation conditions of the ZrCo hydride bed for the D-T gas storage delivery system were proposed based on the ITER FDR 2000 plasma operation scenarios. The disproportionation rate estimated conservatively by the theoretical model indicates that a disproportionation in the ITER basic performance phase can be reduced by <4% even when there is a direct supply from the fuel storage and delivery system beds for all the D-T pulses and by <0.1% when the supply is from the hydrogen isotope separation system.

Nanosize Effects on Hydrogen Storage in Palladium

The size dependencies of the hydrogen-storage properties in polymer-coated Pd nanoparticles with diameters of 2.6 ± 0.4 and 7.0 ± 0.9 nm were investigated by a measurement of hydrogen pressure-composition isotherms. Their storage capacities per constituent Pd atom in the particles decreased with decreasing particle size, whereas the hydrogen concentrations in the two kinds of nanoparticles were almost the same and 1.2 times as much, respectively, as that in bulk palladium after counting zero hydrogen occupancy on the atoms in the first surface layer of the particles. Furthermore, apparent changes in hydrogen absorption behavior with decreasing particle size were observed, that is, a narrowing of the two-phase regions of solid-solution and hydride phases, the lowering of the equilibrium hydrogen pressure, and a decrease in the critical temperature of the two-phase state. By analyzing the isotherms, we quantitatively determined the heat of formation (ΔHα→β) and the entropy change (ΔSα→β) in the hydride form...

NMIJ Constant-Volume Gas Thermometer for Realization of the ITS-90 and Thermodynamic Temperature Measurement

The constant-volume gas thermometer (CVGT) of the National Metrology Institute of Japan (NMIJ), AIST with 3He as the working gas is used as an interpolating gas thermometer to realize the International Temperature Scale of 1990 (ITS-90) from 3 K to 24.5561 K and as a relative gas thermometer for thermodynamic temperature measurement calibrated at the triple point (TP) of Ne. The standard uncertainties of the realization and measurement are estimated to be 0.58 mK and 0.86 mK at a maximum in the mentioned temperature range, respectively. The maximum difference between both temperatures is about 1 mK. In the calibration of the CVGT, the TP of equilibrium hydrogen (e-H2) is corrected for isotopic composition as specified in the Technical Annex for the ITS-90. The ambiguity of the TP of Ne due to the variability in isotopic composition is included in the uncertainty. Although the CVGT was also used in 2004 to realize the ITS-90, it was modified for the present experiment to reduce some measurement uncertainty components and the working gas was replaced with a higher-isotopic-purity gas. The results from 2004 were recalculated by correcting for the isotopic composition of e-H2 and differ insignificantly from the present results, except for a wider scatter.

Hydrogen Transport in a Coupled Elastoplastic-Diffusion Analysis near a Blunting Crack Tip

The role of hydrogen in hydrogen embrittlement, stress corrosion cracking and hydrogen induced cracking has been largely determined. The hydrogen cracking problem in metallurgical fields has been studied for many years. In spite of that, it is still not possible to explain exactly how the presence of hydrogen within the metal structure leads to hydrogen embrittlement and crack formation. Hydrogen-enhanced localized plasticity (HELP) is an acceptable mechanism of hydrogen embrittlement and hydrogen-induced cracking in materials. In the present work, a finite element analysis is implemented to estimate the large deformation elasto-plastic behavior of the material in conjunction with the hydrogen diffusion analysis results. Hydrogen is highly mobile and can diffuse through the crystal lattice dissolving into its interstitial sites. It is necessary to assume the model which can describe the hydrogen diffusivity near the blunting crack tip as well as the large deformation phenomena. Finite element analysis is here employed to solve the coupled boundary-value problem of large strain elasto-plasticity and equilibrium hydrogen distributions ahead of a blunting crack tip by taking into consideration the effect of hydrogen on local flow stress.

Thermodynamics of Gaseous Hydrogen and Hydrogen Transport in Metals

AbstractThe thermodynamics and kinetics of hydrogen dissolved in structural metals is often not addressed when assessing phenomena associated with hydrogen-assisted fracture. Understanding the behavior of hydrogen atoms in a metal lattice, however, is important for interpreting materials properties measured in hydrogen environments, and for designing structurally efficient components with extended lifecycles. The assessment of equilibrium hydrogen contents and hydrogen transport in steels is motivated by questions raised in the safety, codes and standards community about mixtures of gases containing hydrogen as well as the effects of stress and hydrogen trapping on the transport of hydrogen in metals. More broadly, these questions are important for enabling a comprehensive understanding of hydrogen-assisted fracture. We start by providing a framework for understanding the thermodynamics of pure gaseous hydrogen and then we extend this to treat mixtures of gases containing hydrogen. An understanding of the thermodynamics of gas mixtures is necessary for analyzing concepts for transitioning to a hydrogen-based economy that incorporate the addition of gaseous hydrogen to existing energy carrier systems such as natural gas distribution. We show that, at equilibrium, a mixture of gases containing hydrogen will increase the fugacity of the hydrogen gas, but that this increase is small for practical systems and will generally be insufficient to substantially impact hydrogen-assisted fracture. Further, the effects of stress and hydrogen trapping on the transport of atomic hydrogen in metals are considered. Tensile stress increases the amount of hydrogen dissolved in a metal and slightly increases hydrogen diffusivity. In some materials, hydrogen trapping has very little impact on hydrogen content and transport, while other materials show orders of magnitude increases of hydrogen content and reductions of hydrogen diffusivity.

Thermodynamical properties of La–Ni–T (T = Mg, Bi and Sb) hydrogen storage systems

The hydrogen absorption properties of LaNi 4.8T 0.2 (T = Mg, Bi and Sb) alloys are reported. The effects of the substitution of Ni in the LaNi 5 compound with Mg, Bi and Sb are investigated. The ability of alloys to absorb hydrogen is characterized by the pressure–composition ( p– c) isotherms. The p– c isotherms allow the determining thermodynamic parameters enthalpy (Δ H des ) and entropy (Δ S des ) of the dehydrogenation processes. The calculated Δ H des and Δ S des data helps to explain the decrease of hydrogen equilibrium pressure in alloys doped with Al, Mg and Bi and its increase in the Sb-doped LaNi 5 compound. Generally, partial substitution of Ni in LaNi 5 compound with Mg, Bi and Sb cause insignificant changes of hydrogen storage capacity compared to the hydrogen content in the initial LaNi 5H 6 hydride phase. However, it is worth to stress that, in the case of LaNi 4.8Bi 0.2, a small increase of H/f.u. up to 6.8 is observed. The obtained results in these investigations indicate that the LaNi 4.8T 0.2 (T = Al, Mg and Bi) alloys can be very attractive materials dedicated for negative electrodes in Ni/MH batteries.

Direct and Reversible Synthesis of AlH3−Triethylenediamine from Al and H2

Aluminum hydride, AlH3, is the most well-known alane. Though thermodynamically unstable under ambient conditions, it is easily prepared in a metastable state that will undergo controlled thermal decomposition to produce H2 and Al at around 100 °C. AlH3 contains 10.1 wt % hydrogen and has a density of 1.48 g/mL and is therefore of interest for on-board automotive hydrogen storage. ΔHf and ΔGf298K for α-AlH3 are −9.9 and 48.5 kJ/mol AlH3, respectively. The latter value yields an equilibrium hydrogen fugacity of ∼5 × 105 atm at 298 K, which is equivalent to a hydrogen pressure of ∼7 × 103 atm. Thus, the direct regeneration of AlH3 from spent Al with gaseous H2 is deemed impractical. This paper describes an alternate approach to the regeneration of AlH3 via a low-temperature, low-pressure, reversible reaction using Ti-doped Al powder and triethylenediamine (TEDA). The adduct is formed in a slurry of the Al powder and a solution of TEDA in THF in contact with H2. The AlH3−TEDA product is insoluble and precipitates from solution. The reaction, forward or reverse, depends on the departure of the actual pressure of H2 gas above or below the equilibrium pressure. Pressure−composition isotherms in the range of 70−90 °C are presented from which thermodynamic data were calculated. A possible reaction mechanism is described. The relevance of this system to hydrogen storage applications is also noted.

A Novel Approach to Enhance the Hydrogen Yield of Biomass Gasification Using CO2 Sorbent

Hydrogen yield of conventional biomass gasification is limited by chemical equilibrium constraints. A novel technique that has the potential to enhance the hydrogen yield by integrating the gasification and absorption reactions has been suggested. The method involves gasification of biomass in presence of a CO2 sorbent. Ethanol was used as the model biomass compound and CaO was the representative sorbent. Equilibrium modeling was used to determine the product gas composition and hydrogen yield. The analysis was done using ASPEN PLUS software (version 12.1) and the Gibbs energy minimization approach was followed. The effects of temperature, pressure, steam/ethanol ratio, and CaO/ethanol ratio on product yield were investigated. Three case studies were conducted to understand the effect of sorbent addition on the hydrogen yield. Thermodynamic studies showed that the use of sorbents has the potential to enhance the equilibrium hydrogen yield of conventional gasification by ∼19% and reduce the equilibrium CO2 content of product gas by 50.2%. It was also found that the thermodynamic efficiency of sorbent-enhanced gasification (72.1%) was higher than conventional gasification (62.9%). Sorbent-enhanced gasification is a promising technology with a potential to improve the yield and lower the cost of hydrogen production.

수소저장합금을 이용한 SMH 액추에이터 시스템 개발

This paper presents development of an special metal hydride(SMH) actuator system using a peltier module. The newly developed simple SMH actuator, consisting of the plated hydrogen-absorbing alloy as a power source, Peltier elements as a heat source and a cylinder with metal bellows as a functioning part, has been developed. The SMH actuator is characterized by its small size, low weight, noiseless operation and a compliance similar to that of human body. A new SMH actuator that uses reversible reactions between the heat energy and mechanical energy of a hydrogen absorbing alloy. It is well known that hydrogen-absorbing alloys can reversibly absorb and desorb a large amount of hydrogen, more than about 1000 times of their own volume. To improve the thermal conductivity of the hydrogen-absorbing alloy, an electro-less copper plating has been carried out. For this purpose, the effects of the electro-less copper plating and the dynamic characteristics of the SMH actuator have been studied. The hydrogen equilibrium pressure increases and hydrogen is desorbed by heating the hydrogen-absorbing alloys, whereas by cooling the alloys, the hydrogen equilibrium pressure decreases and hydrogen is absorbed. The SMH actuator has the characteristic of being light and easy to use. Therefore, it is suitable for medical and rehabilitation applications.

Direct Bioelectrocatalysis by NADP‐Reducing Hydrogenase from Pyrococcus furiosus

AbstractThe direct bioelectrocatalysis by an NAD(P)‐reducing hydrogenase is reported for the first time. In contrast to previous attempts to involve similar enzymes in bioelectrocatalysis [1–4], which were in fact unsuccessful, in our report an effective electrocatalysis by Pyrococcus furiosus hydrogenase is convincingly shown by (i) achievement of the hydrogen equilibrium potential and (ii) a high current of hydrogen oxidation (0.3 mA cm−2 at 100 mV overpotential and at 75 °C). The latter is just a few times lower compared to enzyme electrodes based on NAD(P)‐independent hydrogenases.

Thermodynamic possibilities and constraints for pure hydrogen production by a nickel and cobalt-based chemical looping process at lower temperatures

The reduction of nickel and cobalt oxides by hydrogen, CO, CH 4 and model syngas (mixtures of CO + H 2 or H 2 + CO + CO 2) and oxidation by water vapour has been studied from the thermodynamic and chemical equilibrium points of view. Attention was concentrated not only on convenient conditions for reduction of the relevant oxides to metals at temperatures in the range 400–1000 K, but also on the possible formation of undesired soot, carbides and carbonates as precursors for carbon monoxide and carbon dioxide formation in the steam oxidation step. Reduction of nickel and cobalt oxides (NiO, CoO and Co 3O 4) by hydrogen or CO at such temperatures is feasible. The oxidation of Ni and Co by steam and simultaneous production of hydrogen is thermodynamically the more difficult step at temperatures of 400–900 K. For the Ni–NiO and Co–CoO systems, the formation of corresponding Ni/Co–ferrite or Ni/Co aluminum spinel could be used for a higher hydrogen equilibrium yield. Only such Ni–NiO and Co–CoO systems with the support of ferrite and aluminum spinel formation could be suitable systems for chemical looping production of hydrogen by the chemical looping redox process. Oxidation of mixed Ni/Co–Fe metals or alloys by steam without segregation caused by preferential oxidation of Fe is critical for the ferrites. For processes based on Ni/Co aluminum spinel, reduction to metals is the critical part of the cyclic process. Under strongly reducing conditions, at high CO concentrations/pressures, formation of nickel carbide (Ni 3C) before cobalt carbide Co 2C is thermodynamically favored. Pressurized conditions during the reduction step with CO/CO 2 containing gases enhance the formation of soot and carbon containing carbide and/or carbonate compounds.

Thermodynamic optimization of biomass gasifier for hydrogen production

A thermodynamic equilibrium model was used to predict the chemical composition of the products of biomass gasification. The effects of temperature, pressure, steam biomass ratio (SBR) and equivalence ratio (ER) on the equilibrium hydrogen yield were studied. Gibbs energy minimization approach was used to determine the product gas composition. Wood (designated by CH 1.5 O 0.7 ) was used as the model biomass compound and Stanjan (v 3.93L) software was used. Gasifier, the most critical component of any biomass gasification system, was modeled as an equilibrium reactor and the energy consumption and thermodynamic efficiency were determined. A first law analysis of the gasifier showed that the optimum conditions for hydrogen production occurred at a gasification temperature of 1000 K, SBR of 3, ER of 0.1. Finally, equilibrium calculations were compared with experimental data from literature which showed that for high gas residence times and high gasification temperatures there is a close match of equilibrium results with experimental ones.

Structure and electrochemical characteristics of [formula omitted] ( [formula omitted], 0.25, 0.50 and 0.75) alloys

The structure and electrochemical characteristics of Ni substitution for Mn and Al in AB 2 -type CeMnAl intermetallic compounds are studied. XRD and SEM reveal that Ni partial substitution leads to a phase change of the alloys and new phase to be formed. The electrochemical activity of CeMn 1 - x Al 1 - x Ni 2 x ( x = 0.00 , 0.25, 0.50 and 0.75) alloy is greatly improved and the discharge capacity can increase from 17.93 mAh g - 1 ( x = 0.00 ) to 118.3 mAh g - 1 ( x = 0.75 ) at 298 K and from 68.42 mAh g - 1 ( x = 0.00 ) to 216.1 mAh g - 1 ( x = 0.75 ) at 328 K, respectively. The electrochemical P– C– T curve shows that no hydrogen equilibrium pressure plateau is observed for CeMnAl alloy while the slope of the plateau becomes flatter and longer with increasing Ni content.

Transport of internal electronic energy in atomic hydrogen thermal plasmas

Reactive and internal thermal conductivities for equilibrium hydrogen plasma have been calculated by the Chapman-Enskog method. The equilibrium composition of the plasma is determined by taking consistently into account the number of allowed atomic electronic excited states (EES) as determined by the average interparticle distance. The coefficients depend on the inclusion of realistic cross sections for the interactions with EES. In particular, the interplay between the two coefficients that describe the transport of electronic and ionization energy is analyzed.

Hydrogen storage properties of Mg[BH 4] 2

Among the large variety of possible complex hydrides only few exhibit a large gravimetric hydrogen density and stability around 40 kJ mol −1H 2. Mg[BH 4] 2 is based on theoretical approaches a complex hydride with an equilibrium hydrogen pressure of approximately 1 bar at room temperature and a hydrogen content of 14.9 mass%. The reaction of Li[BH 4] with MgCl 2 at elevated temperatures was investigated as a possible route to synthesize Mg[BH 4] 2. Li[BH 4] reacts with MgCl 2 at a temperature >523 K at a pressure of 10 MPa of hydrogen, where the product contains LiCl and Mg[BH 4] 2. The desorption pc-isotherm of the product obtained at 623 K shows two flat plateaus, which indicates that the decomposition of the product consists of a two-step reaction. The products of the first and the second decomposition reaction were analyzed by means of X-ray diffraction and found to be MgH 2 and Mg, respectively. The enthalpy for the first decomposition reaction was determined to be Δ H = −39.3 kJ mol −1H 2 by the Van’t Hoff plot of the equilibrium measurements between 563 K and 623 K, which is significantly lower than that for pure Li[BH 4] (Δ H = −74.9 kJ mol −1H 2). However, only the second reaction step (MgH 2 → Mg) is reversible at the condition up to 623 K at 10 MPa of hydrogen.

Effect of rare earth on lattice size and equilibrium hydrogen pressure for AB 5-type MmNi 3.55Co 0.75Al 0.30Mn 0.40

We investigated the effect of rare earth in Mm (misch metal) to crystal structure and hydrogenation properties especially lattice size and equilibrium hydrogen pressure in MmNi 3.55Co 0.75Al 0.30Mn 0.40 using X-ray diffraction (XRD) and pressure–composition ( P–C) isotherms measurements. We successfully prepared the alloys, where Mm was composed of M x La 0.81− x Nd 0.14Pr 0.05 (M x = Ce 0.47, Y 0.40, Gd 0.25, Tm 0.20, Lu 0.16). The substitution amount for each alloy was adjusted to appear stoichiometric single phase and to keep the same lattice volume considering atomic radius of each rare earth element. Among these alloys, however, the Ce containing ones studied showed different characteristics in terms of anisotropy of lattice parameters and equilibrium hydrogen pressure to others. All alloys studied showed the same reversible hydrogen content. Significant difference of the enthalpy and entropy of hydride formation have not been observed.