Reversible Hydrogen Sorption Research Articles

Improvement of reversible H storage capacity by fine tuning of the composition in the pseudo-binary systems A2-xLaxNi7 (A = Gd, Sm, Y, Mg)

A2B7 compounds (A = rare earth or Mg, B = transition metal) are widely studied as active materials for negative electrode in Ni-MH batteries. By playing on the substitution rate of both A and B elements, it is possible to prepare various compositions. This strategy will help to improve the properties, for example get a higher reversible hydrogen capacity and a well-adapted hydrogen sorption pressure. Indeed, A can be almost all light rare earths (La to Gd), yttrium and alkaline earth metals (Mg or Ca), whereas B can contain various late transition metals (Mn to Ni). To understand the effects of composition on the physicochemical properties of La2Ni7-based compound, various pseudo-binary systems have been investigated: Gd2-xLaxNi7 (x = 0, 0.6, 1, 1.5), Sm2-xLaxNi7 (x = 0, 0.5, 1, 1.5), Y2-xLaxNi7 (x = 0, 0.4, 0.5, 0.6, 0.8, 1, 1.5, 1.75) and A0.5La1.1Mg0.4Ni7 (A = Sm, Gd and Y). To determine their crystallographic properties, X-ray diffraction analysis was performed followed by Rietveld refinement. Thermodynamic properties regarding reversible hydrogen sorption were investigated at room temperature. Quaternary compounds present drastically improved sorption properties in the frame of practical energy storage applications with reversible capacity equivalent to 400 mAh/g for the compound La1.1Sm0.5Mg0.4Ni7.

Reversible Hydrogen Storage Using Nanocomposites

In the field of energy storage, recently investigated nanocomposites show promise in terms of high hydrogen uptake and release with enhancement in the reaction kinetics. Among several, carbonaceous nanovariants like carbon nanotubes (CNTs), fullerenes, and graphitic nanofibers reveal reversible hydrogen sorption characteristics at 77 K, due to their van der Waals interaction. The spillover mechanism combining Pd nanoparticles on the host metal-organic framework (MOF) show room temperature uptake of hydrogen. Metal or complex hydrides either in the nanocomposite form and its subset, nanocatalyst dispersed alloy phases illustrate the concept of nanoengineering and nanoconfinement of particles with tailor-made properties for reversible hydrogen storage. Another class of materials comprising polymeric nanostructures such as conducting polyaniline and their functionalized nanocomposites are versatile hydrogen storage materials because of their unique size, high specific surface-area, pore-volume, and bulk properties. The salient features of nanocomposite materials for reversible hydrogen storage are reviewed and discussed.

In Situ Modification of a Delafossite-Type PdCoO2 Bulk Single Crystal for Reversible Hydrogen Sorption and Fast Hydrogen Evolution.

The observation of extraordinarily high conductivity in delafossite-type PdCoO2 is of great current interest, and there is some evidence that electrons behave like a fluid when flowing in bulk crystals of PdCoO2. Thus, this material is an ideal platform for the study of the electron transfer processes in heterogeneous reactions. Here, we report the use of bulk single-crystal PdCoO2 as a promising electrocatalyst for hydrogen evolution reactions (HERs). An overpotential of only 31 mV results in a current density of 10 mA cm–2, accompanied by high long-term stability. We have precisely determined that the crystal surface structure is modified after electrochemical activation with the formation of strained Pd nanoclusters in the surface layer. These nanoclusters exhibit reversible hydrogen sorption and desorption, creating more active sites for hydrogen access. The bulk PdCoO2 single crystal with ultrahigh conductivity, which acts as a natural substrate for the Pd nanoclusters, provides a high-speed channel for electron transfer.

Reversible hydrogen sorption behaviors of the 3NaBH4-(x)YF3-(1-x)GdF3 system: The effect of double rare earth metal cations

In the present work, NaBH4 based hydrogen storage materials, 3NaBH4-(x)YF3-(1-x)GdF3 composites, were prepared via mechanical ball milling with different values of x (2/3, 1/2, 1/3). The de-/rehydrogenation thermodynamic and kinetic behaviors of 3NaBH4-(x)YF3-(1-x)GdF3 composites were systematically investigated. These composites showed a single endothermal peak of hydrogen desorption even though two metal fluorides were added simultaneously into NaBH4. All the 3NaBH4-(x)YF3-(1-x)GdF3 composites showed reversible hydrogen sorption ability and the best hydrogen absorption kinetics was observed in the 3NaBH4-0.5YF3-0.5GdF3 composite, with about 2 wt% hydrogen absorbed at 370 °C under 3.2 MPa H2 pressure in 1 h. Its hydrogen absorption kinetic behaviors were correlated closely to a First-order reaction model based on experimental results. According to the pressure-composition-temperature (PCT) tests, the reversible hydrogen storage capacity increases, and the hydrogen desorption enthalpy decreases along with more GdF3 addition. In particular, the desorption enthalpy with regard to the apparent Pauling's electronegativity (χp) of added metal cations can be described as ΔHd = −2748.21χp+3852.99 kJ/mol H2, where χp=(x)∙χp(Y3+)+(1-x)∙χp(Gd3+). This research helps us to clarify the effect of co-addition of two rare earth metal fluorides on reversible hydrogen sorption in NaBH4.

Experimental Investigation of Isobaric specific heat capacity (Cp) of 9-ethylcarbazole in liquid and solid state

Liquid organic hydrides, e.g. 9-ethylcarbazole, are potentially interesting hydrogen storage materials because of their reversible hydrogen sorption properties. In this study, the isobaric specific heat capacity of 9- ethylcarbazole in solid and liquid phases was investigated using adiabatic calorimeter. The experimental setup consisting of two basic components adiabatic calorimeter and pressure unit was developed. To calibrate the apparatus the specific heat of the water was measured. The experimental data points were obtained at 0.1 MPa to 0.88 MPa pressure range and 353 K to 480 K temperature range. The specific heat dependence on pressure and temperature was presented. The increase in specific heat of 9-ethylcarbazole was observed with increasing pressure and temperature for solid phase, while for liquid phase decrease in trend was observed for increasing pressure. Keywords: 9-ethylcarbazole, Adiabatic Calorimeter, Specific Heat, Nitrogen Gas Cylinder

Reversible hydrogen sorption and kinetics of hydrogen storage tank based on MgH2 modified by TiF4 and activated carbon

By doping with 5 wt % TiF4 and activated carbon (AC), onset and main dehydrogenation temperatures of MgH2 significantly reduce (ΔT = 138 and 109 °C, respectively) with hydrogen capacity of 4.4 wt % H2. Up-scaling to storage tank begins with packing volume and sample weight of 28.8 mL and ∼14.5 g, respectively, and continues to 92.6 mL and ∼60.5–67 g, respectively. Detailed hydrogen sorption mechanisms and kinetics of the tank tightly packed with four beds of MgH2TiF4-AC (∼60.5 g) are investigated. De/rehydrogenation mechanisms are detected by three temperature sensors located at different positions along the tank radius, while hydrogen permeability is benefited by stainless steel mesh sheets and tube inserted in the hydride beds. Fast desorption kinetics of MgH2TiF4-AC tank at ∼275–283 °C, approaching to onset dehydrogenation temperature of the powder sample (272 °C) suggests comparable performances of laboratory and tank scales. Hydrogen desorption (T = 300 °C and P(H2) = 1 bar) and absorption (T = 250 °C and P(H2) = 10–15 bar) of MgH2TiF4-AC tank provide gravimetric and volumetric capacities during the 1st-2nd cycles of 4.46 wt % H2 and 28 gH2/L, respectively, while those during the 3rd-15th cycles are up to 3.62 wt % H2 and 23 gH2/L, respectively. Due to homogeneous heat transfer along the tank radius, de/rehydrogenation kinetics superior at the tank center and degrading forward the tank wall can be due to poor hydrogen permeability. Particle sintering and/or agglomeration upon cycling yield deficient hydrogen content reproduced.

Direct Rehydrogenation of LiBH4 from H-Deficient Li2B12H12−x

Li2B12H12 is commonly considered as a boron sink hindering the reversible hydrogen sorption of LiBH4. Recently, in the dehydrogenation process of LiBH4 an amorphous H-deficient Li2B12H12−x phase was observed. In the present study, we investigate the rehydrogenation properties of Li2B12H12−x to form LiBH4. With addition of nanostructured cobalt boride in a 1:1 mass ratio, the rehydrogenation properties of Li2B12H12−x are improved, where LiBH4 forms under milder conditions (e.g., 400 °C, 100 bar H2) with a yield of 68%. The active catalytic species in the reversible sorption reaction is suggested to be nonmetallic CoxB (x = 1) based on 11B MAS NMR experiments and its role has been discussed.

Transformations of Ethanol on Catalysts Based on Nanoporous Calcium Aluminate–Mayenite (Ca12Al14O33) and Mayenite Doped by Copper

Catalytic properties of nondoped and copper-doped Mayenite have been studied. During ethanol conversion and ethanol steam reforming, the initial Mayenite and specimens containing 0.58 and 0.92 wt % of copper have been analyzed. All catalysts are active in both processes. The influence of the ethanol/water mole ratio on product distribution has been studied. In the course of experiments, the fact of reversible hydrogen sorption has been detected upon the thermal treatment of catalysts containing copper.

Hydrogen Desorption Below 150 °C in MgH2–TiH2 Composite Nanoparticles: Equilibrium and Kinetic Properties

Reversible hydrogen sorption coupled with the MgH2 ↔ Mg phase transformation was achieved in the remarkably low 340–425 K temperature range using MgH2–TiH2 composite nanoparticles obtained by reactive gas-phase condensation of Mg–Ti vapors under He/H2 atmosphere. The equilibrium pressures determined by in situ measurements at low temperature were slightly above those predicted using enthalpy ΔH and entropy ΔS of bulk magnesium. A single van’t Hoff fit over a range extended up to 550 K yields the thermodynamic parameters ΔH = 68.1 ± 0.9 kJ/molH2 and ΔS = 119 ± 2 J/(K·molH2) for hydride decomposition. A desorption rate of 0.18 wt % H2/min was measured at T = 423 K and p(H2) ≈ 1 mbar, i.e., close to equilibrium, without using a Pd catalysts. The nanoparticles displayed a small absorption–desorption pressure hysteresis even at low temperatures. We critically discuss the influence exerted by nanostructural features such as interface free energy, elastic clamping, and phase mixing at the single nanoparticle lev...

Reversible hydrogen sorption in the composite made of magnesium borohydride and silica aerogel

Magnesium borohydride Mg(BH4)2 is a promising hydrogen storage material as it releases high hydrogen amount at mild desorption temperatures, but it is still limited by slow dehydrogenation kinetics and harsh conditions are required for rehydrogenation. In this work, composites made of commercial Mg(BH4)2 and synthesized silica aerogel microparticles were prepared by thermal treatment under 120 bar of hydrogen and 200 °C. As a result, the sorption properties of the hydride are improved: calorimetric measurements show that the decomposition temperature is reduced by 60 °C, and the typical 3-steps decomposition mechanism of Mg(BH4)2 changes to a single-step mechanism in range of 220–400 °C. The kinetics of the first dehydrogenation at 300 °C was two times faster in Mg(BH4)2SiO2 composites than in the case of bulk γ-Mg(BH4)2. Additionally, the rehydrogenation of this material at comparatively moderate conditions of 390 °C and 110 bar of H2 is presented for the first time, achieving cyclability with a reversible release of hydrogen up to 6wt% H2. Different amounts of hydrogen were exchanged depending on the working temperature (300 °C or 400 °C) and the presence or absence of silica aerogel. This result indicates that silica aerogel influence the performance of Mg(BH4)2, acting as an additive, which can result in different hydrogenation-dehydrogenation routes in which different amounts and types of intermediates are formed, influencing the kinetics and reversibility.

DETERMINATION OF HYDROGEN CAPACITY STRUCTURAL DEFECTS

Structural defects have an impact on the process of reversible hydrogen sorption in metals. They alter the kinetics of absorption and the hydrogen content in unit volume. A comparative analysis of the kinetics of formation of hydrogen segregations for an edge dislocation, the top of the microcracks and wedge disclinations. As an illustrative example we consider the electrochemical system nickel-boron-hydrogen bond. The kinetics of the process for the wedge disclination obeys a linear law. Hydrogen segregation to the top of microcracks and edge dislocation occurs more slowly. Hydrogen is considered the capacity mentioned structural defects. It has been shown that they do not significantly increase the amount of hydrogen per unit volume. The results of the theoretical analysis are attracted to justify limiting possibilities metals reversible hydrogen sorption.

Study on reversible hydrogen sorption behaviors of a 3NaBH4/HoF3 composite

In this work, the complex hydrogen sorption behaviors in a 3NaBH4/HoF3 composite prepared through mechanical milling were carefully investigated, including the reactions occurred during ball milling and de-/rehydrogenation processes. Different from other rear earth fluorides, the HoF3 can react with NaBH4 during ball milling, leading to the formations of Na–Ho–F and Na–Ho–BH4 complex compounds. The first dehydriding of the 3NaBH4/HoF3 composite can be divided into 4 steps, including the ion exchange between H− and F−, the formation of NaHo(BH4)4, the decomposition of NaHo(BH4)4 and reaction of NaBH4 with Na–Ho–F compounds. The final products, HoB4, HoH3 and NaF, can be rehydrogenated to generate NaBH4 and NaHoF4 with an absorption capacity of 2.3 wt% obtained at 400 °C. Based on the Pressure–Composition–Temperature measurements, the de-/rehydrogenation enthalpies of the 3NaBH4/HoF3 composite are determined to be 88.3 kJ mol−1 H2 and −27.1 kJ mol−1 H2, respectively.

Effects of La fluoride and La hydride on the reversible hydrogen sorption behaviors of NaBH4: a comparative study

Both LaF3 and the in situ formed LaH2 enable the reversible hydrogen sorption in NaBH4. Comparative studies show that La-B phases play the major role for the regeneration of NaBH4 in both the NaBH4+LaF3 and the NaBH4+LaH2 composites while the substitution of F- for H- results in more favorable thermodynamics in the NaBH4+LaF3 composite.

Mechanical alloying of nanocrystalline intermetallic compound TiFe doped with sulfur and magnesium

A series of nanostructured alloys based on TiFe intermetallic compound were synthesized from the metallic elements in a planetary ball mill by solid state mechanical alloying. Mg and S were added as doping components to a Fe–50%(at.) Ti powder mixture. Phase and structure transformations during mechanical alloying and subsequent annealing as well as hydrogen interaction with the alloys prepared were studied. It was shown that reversible hydrogen sorption capacities of the nanostructured alloys based on TiFe intermetallic compound were of 0.6 and 0.7wt.% at room temperature for the alloys with S and Mg, respectively. The alloys studied demonstrated a simplified activation of hydrogenation, especially for the S-containing one.

Synthesis, characterization, and reversible hydrogen sorption study of sodium-doped fullerene

Herein is presented a novel, straightforward route to the synthesis of an alkali metal-doped fullerene as well as a detailed account of its reversible and enhanced hydrogen sorption properties in comparison to pure C60. This work demonstrates that a reaction of sodium hydride with fullerene (C60) results in the formation of a sodium-doped fullerene capable of reversible hydrogen sorption via a chemisorption mechanism. This material not only demonstrated reversible hydrogen storage over several cycles, it also showed the ability to reabsorb over three times the amount of hydrogen (relative to the hydrogen content of NaH) under optimized conditions. The sodium-doped fullerene was hydrogenated on a pressure composition temperature (PCT) instrument at 275 ° C while under 100 bar of hydrogen pressure. The hydrogen desorption behavior of this sodium-doped fullerene hydride was observed over a temperature range up to 375 ° C on the PCT and up to 550 ° C on the thermogravimetric analysis (TGA). Powder x-ray diffraction verifies the identity of this material as being Na6C60. Characterization of this material by thermal decomposition analysis (e.g. PCT and TGA methods), as well as FT-IR and mass spectrometry, indicates that the hydrogen sorption activity of this material is due to the reversible formation of a hydrogenated fullerene (fullerane). However, the reversible formation of fullerane was found to be greatly enhanced by the presence of sodium. It was also demonstrated that the addition of a catalytic amount of titanium (via TiO2 or Ti(OBu)4) further enhances the hydrogen sorption process of the sodium-doped fullerene material.

Manufacturing of Hydride-Forming Alloys from Mixed Titanium-Iron Oxide

Synthesis of TiFebased metal hydride-forming alloy from mixed titanium iron oxide (ilmenite, FeTiO3) was carried out by a two-stage reduction of the latter using H2 and CaH2 as reducing agents. The reversible hydrogen absorption capacity of the TiFe based material was about 0.5 wt. % H, that is significantly lower than the corresponding values (~1.8 wt. % H) reported in the literature. The main reason for that was in too high amount of oxygen present in the as-prepared TiFe alloy. Thus in order to improve the hydrogen absorption of the raw TiFe, the material was further alloyed together with Zr, Cr, Mn, Ni and Cu to yield an AB2 alloy. For the as-prepared AB2 alloy, the reversible hydrogen sorption capacity was about 1.3 wt. % H at P = 40 bar and >1.8 wt. % at P = 150 bar, which is acceptable for stationary applications. Finally, the material was found to be superior when compared to known AB2-type alloys, with regard to their activation and poisoning tolerance.

Ti–V–Mn based metal hydrides for hydrogen storage

• Ti 0.47 V 0.46 Mn and Ti 0.50 V 0.51 Mn alloys were produced by arc melting. • Compositional differences led to different unit cell volumes for the C14 Laves phase. • Change in composition caused a significant change in plateau pressure and hysteresis. Two Ti–V–Mn BCC-Laves phase alloys with the nominal composition Ti 0.5 V 0.5± x Mn ( x = −0.04 and 0.01), were synthesised by arc melting. This compositional difference resulted in different compositions and unit cell volumes for the C14 Laves phase. Ti 0.47 V 0.46 Mn and Ti 0.50 V 0.51 Mn demonstrated reversible hydrogen sorption capacities of 1.53 and 1.56 ± 0.05 wt.% (at 120 bar H 2 at 303 K) respectively, however, the change in composition results in a small change in the enthalpy of hydride decomposition, and a significant change in plateau pressure and hysteresis. This may allow for the plateau pressure to be tuned to meet the requirements of different solid-state hydrogen storage applications.

Mechanical alloying of nanocrystalline intermetallic compound TiFe doped by aluminum and chromium

Abstract A series of nanostructured alloys based on TiFe intermetallic compound were synthesized from the metallic elements in a planetary ball mill by solid state mechanical alloying. Al and Cr were added as doping components to a Fe-50% (at.) Ti powder mixture. Phase and structure transformations during mechanical alloying and subsequent annealing as well as hydrogen interaction with the alloys prepared were studied. It was shown that reversible hydrogen sorption capacity of the nanostructural alloys based on the TiFe intermetallic compound was of 0.7 wt.% at room temperature. The alloys studied demonstrated a simplified activation of hydrogenation. A correlation between the alloys behavior in their reactions with hydrogen and structure parameters of the hydrogenated samples has been discussed.

Reversible hydrogen sorption in NaBH4 at lower temperatures

In the present study, a new hydrogen storage system, being able to reversibly absorb/desorb hydrogen at fairly low temperatures, was developed based on a 3NaBH4–PrF3 composite. It is shown that 3 wt% of reversible hydrogen sorption can be achieved in the 3NaBH4–PrF3 composite at 400 °C with fast kinetics. After the addition of 5 mol% VF3, the dehydrogenation kinetics of the 3NaBH4–PrF3 composite can be significantly improved. The onset dehydriding temperature is lowered down to 46 °C in vacuum, and the dehydrogenation finishes in 2 min at 400 °C. Both the dehydrogenation enthalpy and activation energy of 3NaBH4–PrF3 can be lowered down through the addition of VF3. In particular, the dehydrogenation products of the 3NaBH4–PrF3–5 mol% VF3 composite can be rehydrogenated at a temperature as low as 48 °C with the regeneration of NaBH4. At 84 °C, a reversible hydrogen sorption of about 1.2 wt% can be achieved in the 3NaBH4–PrF3–5 mol% VF3 composite. The improvement in hydrogen sorption properties can be mainly attributed to the formation of the VB2 phase during dehydrogenation as an efficient catalyst, which maintains well its catalytic effect in the re-/dehydrogenation cycles. Based on a series of controlled experiments and phase analyses, the de-/rehydrogenation mechanisms of the 3NaBH4–PrF3 composite without and with VF3 addition are proposed and discussed in detail.

Mechanisms of reversible hydrogen storage in NaBH4 through NdF3 addition

In this work, a reversible hydrogen storage composite, 3NaBH4/NdF3, has been prepared using a mechanical milling method. The de-/rehydrogenation properties as well as the mechanisms of reversible hydrogen sorption in the composite were carefully investigated. Based on the pressure–temperature–composition measurements, the de-/rehydrogenation enthalpies of the 3NaBH4/NdF3 composite are determined to be 86.4 kJ mol−1 H2 and −13.2 kJ mol−1 H2, respectively. The onset dehydriding temperature of the composite is determined to be 413 °C in 0.1 MPa Ar atmosphere and can be as low as 80 °C under vacuum conditions. Analyses revealed that NdB6, Nd2H5 and NaF were formed after the decomposition of the composite, which can be hydrogenated to produce NaBH4 and NaNdF4. The formation of NaNdF4 instead of NdF3 in the hydrogenated products is believed to be responsible for the reduced hydrogen storage capacity, while the intermediate formation of B, Nd and NdB4 during dehydrogenation accounts for the asymmetric hydriding/dehydriding behaviors in the 3NaBH4/NdF3 composite.