Reversible Hydrogen Absorption Research Articles

N doping porous carbon embedded in self-assembled three-dimensional reduced graphene oxide networks for electrochemical hydrogen storage

Electrochemical hydrogen storage can realize reversible hydrogen absorption and desorption at room temperature and pressure, which has attracted extensive attention recently. A nanosheet-like reduced graphene oxide (rGO)-porous carbon composite with N-doping defect is prepared via a facile annealing, followed by hydrothermal and freeze-drying process. After N-doping, the porous carbon materials exhibit rich pore structure, and high pyridine nitrogen and pyrrolic nitrogen content. Adding them into the graphene self-assembly process, the aggregation tendency of graphene sheets can be reduced, the composite shows a free-standing 3D porous structure. Benefit from the synthetic effect between the rGO conductive network, the hierarchical porous structure, and the doping of N atoms, the rGO-N800 delivers a high hydrogen storage capacity of 266.3 mAh g−1 at 200 mA g−1 after 100 cycles. Moreover, the reversible capacities of the composite can reach 288.4, and 267.1 mAh g−1 at 1000 mA g−1 and 2000 mA g−1, respectively. The outstanding electrochemical performance of the composite demonstrates a promising direction for design carbon-based hydrogen storage materials.

Hydrogen Absorption Reactions of Hydrogen Storage Alloy LaNi5 under High Pressure.

Hydrogen can be stored in the interstitial sites of the lattices of intermetallic compounds. To date, intermetallic compound LaNi5 or related LaNi5-based alloys are known to be practical hydrogen storage materials owing to their higher volumetric hydrogen densities, making them a compact hydrogen storage method and allowing stable reversible hydrogen absorption and desorption reactions to take place at room temperature below 1.0 MPa. By contrast, gravimetric hydrogen density is required for key improvements (e.g., gravimetric hydrogen density of LaNi5: 1.38 mass%). Although hydrogen storage materials have typically been evaluated for their hydrogen storage properties below 10 MPa, reactions between hydrogen and materials can be facilitated above 1 GPa because the chemical potential of hydrogen dramatically increases at a higher pressure. This indicates that high-pressure experiments above 1 GPa could clarify the latent hydrogen absorption reactions below 10 MPa and potentially explore new hydride phases. In this study, we investigated the hydrogen absorption reaction of LaNi5 above 1 GPa at room temperature to understand their potential hydrogen storage capacities. The high-pressure experiments on LaNi5 with and without an internal hydrogen source (BH3NH3) were performed using a multi-anvil-type high-pressure apparatus, and the reactions were observed using in situ synchrotron radiation X-ray diffraction with an energy dispersive method. The results showed that 2.07 mass% hydrogen was absorbed by LaNi5 at 6 GPa. Considering the unit cell volume expansion, the estimated hydrogen storage capacity could be 1.5 times higher than that obtained from hydrogen absorption reaction below 1.0 MPa at 303 K. Thus, 33% of the available interstitial sites in LaNi5 remained unoccupied by hydrogen atoms under conventional conditions. Although the hydrogen-absorbed LaNi5Hx (x < 9) was maintained below 573 K at 10 GPa, LaNi5Hx began decomposing into NiH, and the formation of a new phase was observed at 873 K and 10 GPa. The new phase was indexed to a hexagonal or trigonal unit cell with a ≈ 4.44 Å and c ≈ 8.44 Å. Further, the newly-formed phase was speculated to be a new hydride phase because the Bragg peak positions and unit cell parameters were inconsistent with those reported for the La-Ni intermetallic compounds and La-Ni hydride phases.

In situ formation of TiB2 and TiH2 catalyzed Li/Mg based dual-cation borohydride with a low onset dehydrogenation temperature below 100 °C

Chemical complex borohydride is a promising hydrogen storage material due to its large gravimetric and volumetric hydrogen capacities. However, the high dehydrogenation temperature and sluggish kinetics still place strong restrictions on its practical application in the hydrogen storage field. In this work, a synergetic approach of partial cation substitution and catalysis is developed to enhance the hydrogen storage properties of LiBH4. The Li/Mg based dual-cation borohydride (LiMg2(BH4)5, LMBH) was successfully synthesized by wet chemical ball milling of LiBH4 and MgCl2. The optimal (LMBH (4.5:1) sample, LiBH4 and MgCl2 in molar ratios of 4.5:1, possesses a maximum hydrogen desorption capacity (11.27 wt%) and the outstanding initial decomposition temperature (∼250 °C). Importantly, the LMBH (4.5:1) doped with TiF3 shows a remarkable onset dehydrogenation temperature as low as 97.2 °C, which is about 190 °C lower than that of pristine LiBH4. The LMBH (4.5:1) doped with TiF3 system releases 7.98 wt% H2 within 170 min below 350 °C. And the dehydrogenation product of doped composite can reversibly absorb ∼4.72 wt% H2 at a relatively moderate temperature of 280 °C, which is substantially lower than the reversible hydrogen absorption temperature of previous modified borohydride systems. Based on the structural characteristic analyses, the TiF3 reacts with LMBH (4.5:1) to in-situ form actual catalytic components of TiB2 and TiH2 as the actual catalysts for LMBH (4.5:1), resulting in the improved hydrogen re/dehydrogenation properties. The synergetic modification of Li/Mg dual-cation substitution and TiB2/TiH2 catalysis may lead to the development of light-metal borohydrides with outstanding hydrogen storage properties.

Research progress of hydrogen energy and metal hydrogen storage materials

Hydrogen energy has become one of the most ideal energy sources due to zero pollution, but the difficulty of storage and transportation greatly limits the development of hydrogen energy. In this paper, the metal hydrogen storage materials are summarized, including metal alloys and metal-organic framework. TiFe-based hydrogen storage alloys have become one of the most promising materials because of their reversible hydrogen absorption and desorption at room temperature and low hydrogen pressure. However, the first hydrogenation requires activation at high pressure and high temperature, which is not conducive to practical application. This paper reviews the methods to improve the hydrogen storage performance of TiFe-based alloys: (1) High energy ball milling leads to the formation of microcrystalline, nanocrystalline boundaries and a large number of structural defects in the alloy, resulting in a significant increase in hydrogen diffusion channels. Meanwhile, the high surface activity of the ball-milled alloy weakens the bond energy of the Ti–H bond, thus promoting the improvement of the activation performance, hydrogen storage capacity and subsequent hydrogen absorption and desorption kinetics of the TiFe-based alloy. (2) Transition metals and rare earth elements with high valence and high affinity for hydrogen are also introduced to improve the activation performance.

Effects of Zr doping on activation capability and hydrogen storage performances of TiFe-based alloy

Activation difficulty is the key problem limiting the application of TiFe-based hydrogen storage alloys. The addition of transition group elements helps to improve the activation properties of TiFe-based hydrogen storage alloy. In our previous work, the Ti1.08Y0.02Fe0.8Mn0.2 alloy exhibits extremely high hydrogen storage capacity (1.84 wt%) at room temperature with excellent kinetic properties, but it still needs an incubation period of about 1500s. In this study, the composition of Ti1.08Y0.02Fe0.8Mn0.2Zrx (x = 0, 0.02, 0.04, 0.06, 0.08) alloys was prepared by electromagnetic induction melting. The quantitative analysis of elements by energy dispersive spectrometer shows that in the second phase region containing Zr, the content of Ti element is significantly higher than that of Fe. Meanwhile, the first-principle calculation on Zr-doped TiFe system indicates that Zr is more attractive to substitute Ti than Fe. Therefore, the doping of Zr partially replaces the Ti. The solubility of Zr in TiFe is limited, when x ≤ 0.04, the alloy consists of pure TiFe phase. When x > 0.4, the excess Zr forms precipitates, which reduces the reversible hydrogen absorption and desorption capacity of the TiFe alloy. The addition of Zr significantly shortens the activation time and reduces the plateau pressure of TiFe alloys. The Ti1.08Y0.02Fe0.8Mn0.2Zr0.04 alloy can be directly activated without the incubation period and its absolute values of enthalpy change (ΔH) and entropy change (ΔS) are minima (ΔH for 23.2 kJ/mol and ΔS for 83.1 J/mol/K).

Thermodynamic analysis of a metal hydride hydrogen compressor with aluminium substituted LaNi5 hydrides

The operating conditions of a Metal Hydride Hydrogen Compressor (MHHC) is often dictated by the hydride used to build it. This research focuses on finding the appropriate operating conditions for MHHC to get the ideal throughput and efficiency using aluminium based hydrides. For this, hydrogen absorption and desorption characteristics of LaNi5-xAlx (where x is 0, 0.2 and 0.4) hydrides were studied for estimating the suitability of these materials for developing hydrogen compressor. From the Pressure Concentration Isotherms (PCIs) and van't Hoff plot, an estimate of the reversible hydrogen weight percent attainable, equilibrium pressure and absorption and desorption temperature range were collected and the effect of aluminium concentration on these properties was studied. Further thermodynamic analysis was made by calculating the performance parameters like thermal efficiency, isentropic work required, theoretical heat supplied and pressure ratio by varying the operating conditions like supply pressure (3–5 bar), absorption temperatures (20–40 °C), and desorption temperature (80–140 °C). It is observed that the higher aluminium content in the hydride allows the hydrogen compressor to be operated at a lower supply pressure. Whereas lower aluminium content in hydrides give higher thermal efficiency and discharge pressure for a particular desorption temperature, while requiring a higher supply pressure to perform efficiently. The maximum thermal efficiency within the studied operating conditions was found to be 0.24 for LaNi5 at 3 bar supply pressure, 30 °C absorption and 140 °C desorption temperature with a pressure ratio of 8.97.

Structural degradation behavior of Mg2-Pr Ni4 upon hydrogenation

Hydrogenation properties of Mg2-xPrxNi4 (x = 1.0, 1.2 and 1.4) and their structural degradation (amorphization) upon hydrogenation have been investigated using in-situ X-ray diffraction. In Mg1.0Pr1.0Ni4, the crystalline phase was stable up to a temperature of 573 K under 3 MPa of hydrogen pressure and amorphization did not take place. Mg0.6Pr1.4Ni4 was directly transformed to an amorphous hydride, Mg0.6Pr1.4Ni4H~7.2, while Mg0.8Pr1.2Ni4 transformed to amorphous Mg0.8Pr1.2Ni4H~6 through the formation of Mg0.8Pr1.2Ni4H~4 having an orthorhombic structure. While reversible hydrogen absorption and desorption was observed in the first plateau region between Mg0.8Pr1.2Ni4 and Mg0.8Pr1.2Ni4H~4. First principles calculation indicate that the elastic modulus and bulk modulus decreased with increase of the Pr content and hydrogen content in Mg2-xPrxNi4 suggesting that decrease of bulk modulus induce amorphization upon hydrogen absorption. These results clearly indicate that the hydrogenation properties, the stability of crystalline hydride and amorphization behavior strongly depend on the chemical composition of Mg2-xPrxNi4 and their hydrogen content.

Hydrogen absorption-desorption characteristic of (Ti0.85Zr0.15)1.1Cr1-xMoxMn based alloys with C14 Laves phase

The microstructure and hydrogen absorption-desorption characteristic of (Ti0.85Zr0.15)1.1Cr1-xMoxMn (x ​= ​0.05, 0.1, 0.15, 0.2 ​at.%) alloys were investigated. The results showed that the corresponding alloys were determined as a single phase of C14-type Laves structure. With the increase of Mo content, the maximum and reversible hydrogen absorption capacity decreased, the slope factor Hf increased. Among the studied alloys, (Ti0.85Zr0.15)1.1Cr0.95Mo0.05Mn had the best overall properties for practical application of hydrogen storage materials. The maximum and reversible hydrogen storage capacity were 1.76 ​wt% and 1.09 ​wt%, the slope factor Hf was 0.51, and its dissociation enthalpy (ΔHd) and entropy change (ΔSd) were 23.1 ​kJ ​mol−1H2, 93.8J ​K−1mol−1H2 at 303K, respectively. By studying the dissociation pressures of the synthesized metal hydrides, it was found that Mo had a special effect on the dissociation pressure of Ti–Zr–Cr–Mo–Mn alloys. Among the four alloys, (Ti0.85Zr0.15)1.1Cr0.95Mo0.05Mn alloy had the largest hydrogen absorption capacity and the fastest hydrogen desorption rate, which can meet the commercialization demand of hydrogen fuel cell hydrogen supply system.

The Crystal Structures in Hydrogen Absorption Reactions of REMgNi4-Based Alloys (RE: Rare-Earth Metals)

REMgNi4-based alloys, RE(2−x)MgxNi4 (RE: rare-earth metals; 0 &lt; x &lt; 2), with a AuBe5-type crystal structure, exhibit reversible hydrogen absorption and desorption reactions, which are known as hydrogen storage properties. These reactions involve formation of three hydride phases. The hydride formation pressures and hydrogen storage capacities are related to the radii of the RE(2−x)MgxNi4, which in turn are dependent on the radii and compositional ratios of the RE and Mg atoms. The crystal structures formed during hydrogen absorption reactions are the key to understanding the hydrogen storage properties of RE(2−x)MgxNi4. Therefore, in this review, we provide an overview of the crystal structures in the hydrogen absorption reactions focusing on RE(2−x)MgxNi4.

Improvement of hydrogen storage characteristics of catalyst free magnesium nanoparticles prepared by wet milling

Magnesium is one of the potential candidates for on-board hydrogen storage, but slow hydrogenation kinetics and unfavourable thermodynamics limits its practical implementation. To improve the hydrogenation characteristics, nanocrystalline magnesium was prepared by a simple wet milling method without addition of heavy metal catalyst. Compared to micro-crystalline Mg, developed nanocrystalline Mg exhibits improved hydrogen storage properties showing extended plateau region in the pressure-composition-temperature curves with higher hydrogen storage capacity (6.24 wt% at 300°C). Hydrogenation and dehydrogenation kinetics is found to follow Kolmogorov−Johnson−Mehl−Avrami activation energy model confirming the involvement of nucleation-growth-impingement mechanism. Prolonged ball milling leads to quite fast hydrogenation kinetics (upto 90% of the saturation value in 15.5 minutes at 250°C) and leads to substantial decrease in the activation barrier. The activation energy for hydrogenation is found to be 68.88 kJ mol−1 for 8 hours ball milled sample. Present study established a simple and scalable method for nanocrystalline Mg, which can undergo reversible hydrogen absorption and desorption with improved performance without using any additional catalyst.

Hydrogen storage performance of the multi-principal-component CoFeMnTiVZr alloy in electrochemical and gas-solid reactions.

The single-phase multi-principal-component CoFeMnTiVZr alloy was obtained by rapid solidification and examined by a combination of electrochemical methods and gas–solid reactions. X-ray diffraction and high-resolution transmission electron microscopy analyses reveal a hexagonal Laves-phase structure (type C14). Cyclic voltammetry and electrochemical impedance spectroscopy investigations in the hydrogen absorption/desorption region give insight into the absorption/desorption kinetics and the change in the desorption charge in terms of the applied potential. The thickness of the hydrogen absorption layer obtained by the electrochemical reaction is estimated by high-resolution transmission electron microscopy. The electrochemical hydrogen storage capacity for a given applied voltage is calculated from a series of chronoamperometry and cyclic voltammetry measurements. The selected alloy exhibits good stability for reversible hydrogen absorption and demonstrates a maximum hydrogen capacity of ∼1.9 wt% at room temperature. The amount of hydrogen absorbed in the gas–solid reaction reaches 1.7 wt% at 298 K and 5 MPa, evidencing a good correlation with the electrochemical results.

Metallo-N-Heterocycles - A new family of hydrogen storage material

Storing hydrogen efficiently in condensed materials is a key technical challenge. Tremendous efforts have been given to inorganic hydrides containing B–H, Al–H and/or N–H bonds, while organic compounds with a great variety and rich chemistry in manipulating C–H and unsaturated bonds, however, are undervalued mainly because of their unfavourable thermodynamics and selectivity in dehydrogenation. Here, we developed a new family of hydrogen storage material spanning across the domain of inorganic and organic hydrogenous compounds, namely metallo-N-heterocycles, utilizing the electron donating nature of alkali or alkaline earth metals to tune the electron densities of N-heterocyclic molecules to be suitable for hydrogen storage in terms of thermodynamic properties. Theoretical calculations reveal that the enthalpies of dehydrogenation (ΔHd) of these metallo-N-heterocycles are dependent on the electronegativity of the metals. In line with our calculation results, sodium and lithium analogues of pyrrolides, imidazolides and carbazolides of distinct structures were synthesized and characterized for the first time, where the cation-π interaction was identified. More importantly, a reversible hydrogen absorption and desorption can be achieved over lithium carbazolide which has a hydrogen capacity as high as 6.5 ​wt% and a suitable enthalpy of dehydrogenation of 34.2 ​kJ ​mol−1-H2 for on-board hydrogen storage.

Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction

Aluminium-based complex hydrides (alanates) composed of metal cation(s) and complex anion(s), [AlH4]− or [AlH6]3− with covalent Al–H bonds, have attracted tremendous attention as hydrogen storage materials since the discovery of the reversible hydrogen desorption and absorption reactions on Ti-enhanced NaAlH4. In cases wherein alkaline-earth metals (M) are used as a metal cation, MAlH5 with corner-sharing AlH6 octahedron chains are known to form. The crystal structure of SrAlH5 has remained unsolved although two different results have been theoretically and experimentally proposed. Focusing on the corner-sharing AlH6 octahedron chains as a unique feature of the alkaline-earth metal, we here report the crystal structure of SrAlD5 investigated by synchrotron radiation powder X-ray and neutron diffraction. SrAlD5 was elucidated to adopt an orthorhombic unit cell with a = 4.6226(10) Å, b = 12.6213(30) Å and c = 5.0321(10) Å in the space group Pbcm (No. 57) and Z = 4. The Al–D distances (1.77–1.81 Å) in the corner-sharing AlD6 octahedra matched with those in the isolated [AlD6]3− although the D–Al–D angles in the penta-alanates are significantly more distorted than the isolated [AlD6]3−.

Enhanced hydrogen storage capacity and reversibility of LiBH4 encapsulated in carbon nanocages

In this work, we first obtained carbon nanocages (CNCs) with nanoporous structure and high specific surface area via a template synthesis method, and then prepared a LiBH4@CNCs hydrogen storage composite by combining melting LiBH4 into the CNCs. Temperature programmed desorption (TPD) analyses show that the composite starts to release hydrogen at 200 °C, with the maximal desorption peak occurs at about 320 °C, which is 180 °C lower than that of the pure LiBH4. Also, the final hydrogen desorption capacity reaches 7.5 wt.%. We also see enhanced reversible properties of the composite, of which 78% initial hydrogen is absorbed after five de/rehydrogenation cycles at 400 °C. The further studies show that the LiBH4 can react with the oxygen-containing group of CNCs to form LiBO2 during the infiltration process. The LiBO2 dispersed on the scaffold of CNCs further reacts with LiBH4 to release more hydrogen, and the reaction product Li3BO3 as an efficient catalyst can significantly improve the reversible hydrogen storage properties of the LiBH4. The synergetic effect of nanoconfinement of CNCs and catalysis of Li3BO3 is proved to be largely beneficial for the decomposition process and reversible hydrogen absorption of LiBH4.

High-voltage asymmetric supercapacitor based on MnO2 nanotubes//active carbon-multiwalled carbon nanotubes

Active carbon (AC) composited with multiwall carbon nanotubes (CNTs) is synthesized through a high-temperature process for application as a negative electrode material of capacitors. Highly porous interconnected CNTs are uniformly coated onto the surface of AC sheet with a large area that reversibly absorbed hydrogen, resulting in a supercapacitor with larger working voltage and higher pseudocapacitance. A MnO2 nanotubes//AC–CNTs asymmetric electrochemical capacitor is assembled within a wide voltage region of 0–2.4 V in 2.0 M Li2SO4 aqueous electrolyte. Moreover, high energy density and power density, as well as superior cycling stability with >92 % capacitance retention over 6000 cycles, are observed. The reversible hydrogen absorption of the negative electrode may have practical applications in supercapacitors with high energy density and power density. The AC–CNTs composite was synthesized through a high-temperature process for application as a negative electrode which electrically sorbed hydrogen that not only enlarge the potential window, but also improve the pseudocapacitance, which having excellent energy density and power density.

Hydrogen absorption-induced reversible change in magnetic properties of Co–Pd alloy films

The effects of reversible hydrogen absorption on the magnetism of Co–Pd alloy thin films were investigated. Evident enhancement of magnetic coercivity Hc and squareness, measured by magneto optical Kerr effect (MOKE), was observed in the magnetic hysteresis loops of films with Pd content of 61%, 76%, and 86%, whereas no observable changes were noted in the MOKE hysteresis loops of Co-rich alloy films. For Co39 Pd61, perpendicular magnetic anisotropy increased as film thickness increased from 10 to 20 nm. Hydrogenation induced three times enhancement of perpendicular Hc for 20 nm Co39 Pd61, whereas the Hc change in 10 nm Co39 Pd61 was within 10%. A Pd-rich alloy composition and appropriate film thickness for perpendicular magnetization are both crucial for hydrogen absorption-induced effect on magnetic properties, i.e. the enhancement of Hc and squareness as well as the reduction of Kerr rotation angle.

In Situ Neutron Powder Diffraction of Li6C60 for Hydrogen Storage

Li6C60 is so far the best performing fullerene-based hydrogen-storage material. The mechanism of its reversible hydrogen absorption is not, however, totally known. Here, we report the thermal evolution of Li6C60 upon deuterium absorption up to 330 °C and under 60 bar deuterium gas pressure using in situ high-intensity neutron powder diffraction. The temporal resolution of the collected data allowed the hydrogenation of Li6C60 and the segregation of lithium hydride (here LiD) processes to be distinguished from a mechanistic point of view. During absorption, Li6C60 undergoes several phase transitions, involving the partial segregation of Li in the form of hydride and the expansion of the face-centered cubic (fcc) lattice, followed by a body-centered cubic (bcc) rearrangement of the deuterated fullerenes. The amount of absorbed deuterium was determined by the analysis of the variation in the scattered neutron intensity and confirmed by an ex situ desorption measurement. This analysis clarifies the complex ph...

Reversible hydrogen absorption in a Ti-6Al-4V alloy produced by mechanical alloying

Hydrogen absorption in a Ti-6Al-4V alloy prepared by ball milling was investigated in view of the reversible storage of hydrogen in a solid state. The material characterization by X-ray and neutron diffractometry demonstrated the formation of a single α phase whose unit cell expanded during the hydrogen absorption. The maximum storage capacity of this α phase was 1.8 wt% H and no hydride formation was observed. The existence of such a particular supersaturated hexagonal phase was attributed to the strongly defective structure formed by the mechanical alloying process.

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 &gt;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.

Impact of hydrogen absorption on crystal structure and magnetic properties of geometrically frustrated Nd2Ni2In

Nd2Ni2In orders antiferromagnetically at TN=8K. A possible first-order type of the phase transition can be related to the frustrated lattice of the Shastry–Sutherland type. The transition does not shift in magnetic field but turns into a ferromagnetic transition in magnetic fields exceeding 0.3T. Powder neutron diffraction determined the magnetic structure with Nd moments oriented mutually perpendicular along the directions of the 〈110〉 type. Large change of magnetic entropy in weak magnetic fields leads to a giant magnetocaloric effect. Reversible hydrogen absorption in pressures of several bar leads to the hydride Nd2Ni2InH≈7 achieved through the sequence of intermediate hydrides. The highest hydride has an orthorhombic distortion and volume expansion exceeding 23%. It is antiferromagnetic below TN≈3K.