Enthalpy Of Hydrogen Absorption Research Articles

Effect of industrial grade raw materials and its associated impurities on first hydrogenation of BCC solid solution alloys

This study explores the effects of using industrial-grade raw materials on the hydrogen storage properties of body-centered cubic (BCC) solid solution alloys. Industrial scrap metals were chosen as the raw material, and the desired alloys were synthesized using a vacuum arc melting furnace. Instead of using pure vanadium (V), different inexpensive industrial substitutes such as low-grade vanadium (V), vanadium nitride (VN), vanadium oxide (VO), and ferrovanadium (FeV) were utilized. The crystal structure, morphology, first hydrogenation, thermodynamics, and cyclability of the prepared alloys were analyzed by using XRD, SEM-EDS, and XPS methods. The crystal structure and morphology analysis revealed multiphase alloys in all the prepared alloys and a Ti rich third phase in the VN sample, which was absent otherwise. The first hydrogenation was performed at room temperature under a hydrogen pressure of 2 MPa without any prior heat treatment. The VO alloy displayed negligible hydrogen absorption during first hydrogenation, while the V, VN, and FeV alloys showed maximum hydrogen storage capacities of 3.49 wt%, 2.47 wt%, and 2.18 wt%, respectively. The presence of oxygen hinders the activation of the VO alloy and requires two activation cycles to activate the sample. A short-term cyclability analysis showed a reversible hydrogen storage capacity of 2 wt%. The change in enthalpy of hydrogen absorption and desorption for V alloy were calculated to be −36.73 ± 8.6 and 57.34 ± 8.3 kJ/mol H2, respectively. One of the prominent advantages of utilizing scrap raw materials was the substantial reduction in overall raw material costs, which saw an impressive 95% decrease when compared to using pure raw materials. These results highlight the economic benefits of incorporating recovered industrial scrap into hydrogen storage alloys.

Microstructure and hydrogen storage properties of MgH2/MIL-101(Cr) composite

In this paper, a new hydrogen storage composite based on magnesium hydride and metal-organic framework MIL-101(Cr) (an acronym for Material Institute Lavoisier) has been mechanically synthesized and investigated. The hydrogen sorption and desorption behavior in the composite was investigated for the temperature and pressure ranges of (593−653) K and (0−3) MPa, respectively. According to the pressure-composition-temperature isotherms of hydrogen sorption/desorption, the MgH2–5 wt%MIL-101(Cr) composite starts to absorb hydrogen at a lower pressure at 593 K. In addition, the hydrogen release peak for composite shifts to lower temperatures by about 140 K compared to the pure milled MgH2 during temperature programmed desorption at a heating rate of 6 K/min. The activation energy of hydrogen desorption from the composite is 120 ± 2 kJ/mol, which is 36% lower than the activation energy of hydrogen desorption from magnesium hydride (189 ± 2 kJ/mol). The enthalpy of hydrogen absorption was found to be 73 kJ/mol H2 and 60 kJ/mol H2 for milled MgH2 and MgH2–5 wt%MIL-101(Cr) composites, respectively. It is showed that the MIL-101(Cr) MOF structures decompose during ball milling and the chromium oxide nanoparticles form a core-shell structure with MgH2 particles. Thus, composite has better sorption and desorption properties than pure magnesium/magnesium hydride due to the nanoconfinement of MgH2. The chromium oxide nanoparticles act as active sites on the surface of the magnesium particles and facilitate the dissociative chemisorption or recombinative desorption of hydrogen. The main regularities of the phase transition in the magnesium-hydrogen system for the composite and magnesium hydride during dehydrogenation have been studied for temperatures in the range of 298–750 K. The in situ analysis of the phase transitions during the dehydrogenation of MgH2 and MgH2–5 wt%MIL-101(Cr) composite indicates a pronounced catalytic effect of the addition of MIL-101(Cr) to the Mg/MgH2. Based on the experimental results and ab initio calculations, a mechanism for the sorption and desorption of hydrogen by the composite has been proposed.

The electronic, elastic, and structural properties of Ti–Pd intermetallics and associated hydrides from first principles calculations

Using an ab initio density functional approach, we report on the ground-state phase stabilities, enthalpies of formation, electronic, and elastic properties of the Ti–Pd alloy system. The calculated enthalpies of formation are in excellent agreement with available calorimetric data. We found a linear dependence between the calculated enthalpies of formation of several intermetallic structures and the Pd-concentration, indicating that each of these compounds has a very limited composition range. The elastic constants for many of these Ti–Pd intermetallics were calculated and analyzed. The B2 TiPd phase is found to be mechanically unstable with respect to the transformation into the monoclinic B19′ structure. A series of hydrides, Ti 2PdH x ( x = 1, 1.5, 2, 3, 4), have been investigated in terms of electronic structure, enthalpies of hydrogen absorption, and site preference of H atoms. Our results illustrate the physical mechanism for hydrogen absorption in term of the charge transfer, and explain why TiPd 2 does not form a stable hydride.

Kinetics of Hydrogen Isotope Absorption for Well-Annealed Palladium-Platinum Alloys

Absorption kinetics of protium and deuterium for Pd, Pd-4 at%Pt and Pd-8 at%Pt were studied in a dilute hydrogen concentration region in a temperature region from 274 to 357 K by means of constant volume method, where samples were annealed well at 973 K under vacuum before measurements to remove defects induced by sample preparation. It was found that protium had larger rate constants for adsorption, lower rate constants for desorption and larger diffusion constants than those of deuterium within the examined temperature region. The activation energy of hydrogen absorption for both hydrogen isotopes was almost null for all of the samples used. The activation energy of desorption for deuterium was smaller than that for protium. It was attributed to the difference in the enthalpy of hydrogen absorption into metal in dilute hydrogen concentration region between protium and deuterium. These features and trends observed in the alloying effect were supported by the ab initio calculations for small clusters.

Hydrogen absorption–desorption behavior of zirconium-substituting Ti–Mn based hydrogen storage alloys

Hydrogen storage properties of zirconium substituting Ti–Mn based Laves phase alloys with the formula Ti1−XZrXMn1.4 (X=0, 0.1, 0.2, 0.3 and 0.4) were evaluated by pressure-composition (PC) isotherm tests. Their crystallographic structures were identified by X-ray diffraction (XRD). The experimental results showed that their maximum hydrogen storage capacity (H/M, M=Ti1−XZrXMn1.4) increased with increasing X. The value of H/M for X=0.4 reached up to 2.916 which corresponds to 2.05 wt.% of hydrogen in the hydride, while the maximum reversible hydrogen storage capacity of the alloys appeared at X=0.1. The introduction of zirconium into the alloy did not cause any change in the phase constitution. C-14 type Laves phase was still predominant in the alloy while the lattice parameters a and c increased with increasing content of zirconium substituting for titanium. The introduction of zirconium increased the changes of entropy and enthalpy of hydrogen absorption. Activation tests showed that Ti0.9Zr0.1Mn1.4 alloy could react with hydrogen quickly under the condition of 273K and 9 atm of hydrogen.

Kinetics of hydrogen absorption by nickel powder with added palladium, copper, and nickel from nickel-chloride reduction by hydrogen

Absorption of hydrogen by nickel powder, obtained from a reduction of dehydrated nickel-chloride by hydrogen, in the presence of 0.1 mass.% of palladium, copper, and nickel from nickel-formate decomposition has been investigated. A stereological analysis of the powders revealed relatively rounded and similar shaped particles of sizes in the range D x = 0.321–2.085 μm. The largest value of the mean particle diameter is observed for the pure nickel powder ( D x = 2.085 μm), and the lowest for the powder with added palladium ( D x = 0.321 μm). Kinetics of hydrogen absorption in a temperature interval of 80–350 °C have been investigated and the activation energy, absorption enthalpy, rate constants of the reactions, and the frequency factors determined. Enthalpy of hydrogen absorption by pure nickel powder amounts − Δ H = 588 J/g, increasing in the presence of additives, being −Δ H =2916 J/g in the case of palladium added, −Δ H = 1454 J/g and −Δ H = 1228 J/g when copper and nickel were added. The maximum absorption enthalpy of the sample with added palladium can be explained by the influence of the “spillover” effect and the particle sizes (the smallest ones), while a positive effect of added copper is thought to be a consequence of the weakening of bonds in the lattice of nickel due to copper solubility and somewhat smaller particles. The influence of added nickel, obtained by nickel-formate decomposition, on the absorption increase resulted from a decrease in the particle size.

Spill-over process of hydrogen sorption on palladized alumina, yttria and zeolite 4A

Doping of alumina, yttria and zeolite 4A with small quantities of palladium (down to 0.025%) was done. It was shown that these oxides, which do not normally absorb hydrogen, after the doping acquire a considerable capacity for hydrogen absorption. The sorption of hydrogen is occurring by the spill-over effect from metallic palladium to the oxide. The process is exothermal, taking place in two stages between 60 and 350 °C. Activation energies of the first stage range from 120 to 167 kJ mol−1 and for the second one from 20 to 30 kJ mol−1. After cooling to room temperature in hydrogen flow, the samples are able to absorb considerable quantities of oxygen which reacts exothermally with the previously formed hydride. On next exposition to hydrogen, a vigorous reaction of it with the adsorbed oxygen is taking place already at room temperature. Enthalpies of hydrogen absorption, — ΔH, are of the order of 10 kJ g−1, showing a tendency of increase after repeated exposures to hydrogen.

Enthalpy of Hydrogen Absorption in Palladium Deposited on Al2O3 and TiO2 Supports

The potentials of the Pd/TiO2 and Pd/Al2O3 catalysts were measured during saturation with hydrogen and during oxidation of the absorbed hydrogen with Ce(IV) in the medium of 0.5M-H2SO4. From the potential values attained in the coexistence region of the α- and β-hydride phases the enthalpy of hydrogen absorption, ∆Hab in Pd deposited on various supports was evaluated. With standard supports Degussa, ∆Hab approaches the value measured on Pt black; a marked decrease of the absorption enthalpy was observed on the support TiO2 of domestic provenience.

Effect of Pd–TiO2 interaction on the enthalpy of hydrogen absorption

The uptake of hydrogen (chemisorption and absorption) by palladium supported on titania has been measured volumetrically at various temperatures. On increasing the hydrogen pressure, α-phase palladium hydride absorbed hydrogen and transformed into β-phase. The transition pressure increased with the measuring temperature. The enthalpy of the transition was decreased by increasing the temperature for reduction pretreatment. These variations are attributed to electronic interactions between the metallic palladium and the reduced support (TiOx).