Hydrogen Absorption Desorption Research Articles

In situ incorporation of highly dispersed nickel and vanadium trioxide nanoparticles in nanoporous carbon for the hydrogen storage performance enhancement of magnesium hydride

Slow hydrogen absorption-desorption kinetics and high thermal stability hinder the industrial application of Mg/MgH2 systems. In order to overcome these drawbacks, the in situ incorporation of highly dispersed nickel and vanadium trioxide nanoparticles in nanoporous carbon ((Ni-V2O3)@C) was introduced to enhance the hydrogen storage performance of Mg/MgH2. It was found that the 10 wt% (Ni-V2O3)@C-containing sample demonstrated excellent hydrogen storage performance. The 10 wt% (Ni-V2O3)@C-containing sample could uptake hydrogen at room temperature, and its initial hydrogenation temperature was reduced by 100 °C as compared to that of pristine MgH2. Moreover, this system could absorb 5.50 wt% of H2 at 25 °C and release 6.05 wt% of H2 at 275 °C in 10 min. In addition, the hydrogenation and dehydrogenation activation energies of the 10 wt% (Ni-V2O3)@C-containing sample were calculated as 42.1 kJ·mol−1 and 84.6 kJ·mol−1, respectively, which were 46.8 kJ·mol−1 and 51.6 kJ·mol−1 lower than those of pristine MgH2, respectively. Mechanism analysis results revealed that V2O3 was partially converted into VO during milling with MgH2, and Ni reacted with Mg to form in situ Mg2Ni after the first dehydrogenation. The in situ Mg2Ni/Mg2NiH4 coating around Mg/MgH2 acted as a “hydrogen pump” to drive hydrogen diffusion and dissociation, and the presence of C inhibited the agglomeration of Mg/MgH2 particles. Therefore, the addition of (Ni-V2O3)@C was found to be a good strategy to improve the hydrogen storage performance of MgH2.

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.

Hydrogen absorption–desorption characteristics of R3MgNi14(R = Nd, Gd and Er) alloys

Hydrogen absorption–desorption characteristics of R3MgNi14(R = Nd, Gd and Er) alloys

Roles of in situ-formed NbN and Nb2O5 from N-doped Nb2C MXene in regulating the re/hydrogenation and cycling performance of magnesium hydride

The industrial use of magnesium hydride (MgH2) as a potential solid hydrogen storage material is limited because of its poor thermodynamic properties. In the present work, nitrogen-doped niobium carbide-supported niobium pentoxide (N-Nb2O5@Nb2C) was prepared using Nb2AlC and NH3·H2O as precursors and then employed to enhance the hydrogen storage properties of MgH2. It was found that in situ-formed NbN and Nb2O5 in N-Nb2O5@Nb2C-doped MgH2 could destabilize MgH2, improving the hydrogen storage properties of MgH2 at low temperatures. The N-Nb2O5@Nb2C-doped MgH2 composite started to release hydrogen at 178 °C and could uptake 5.0 wt% of hydrogen within 1.95 min at 90 °C and within 5 h at 30 °C. The capacity retention ratio of N-Nb2O5@Nb2C-doped MgH2 was 98.6%, which was much higher than that of additive-free MgH2 (73.5%) after 100 hydrogen absorption–desorption cycles. The mechanism analysis revealed that the presence of NbN and Nb2O5 could restrain the grain size of MgH2, provide more active sites and hydrogen diffusion paths, weaken the interaction between Mg and H, and elongate the length of Mg-H bond; thus, the cyclic stability and reversible hydrogen storage performance of MgH2 were significantly improved.

Effect of varying Ni content on hydrogen absorption–desorption and electrochemical properties of Zr-Ti-Ni-Cr-Mn high-entropy alloys

The crystal structure, pressure composition isotherms, and electrochemical properties of Zr0.2Ti0.2Ni0.2+xCr0.2Mn0.2 (x = 0, 0.025, 0.05, 0.075, and 0.1) high-entropy alloys (HEAs) were investigated. The crystal structures of all the HEAs consisted of two phases: a primary phase with a C14-type (Zr0.5Ti0.5)Mn2 hexagonal structure and a secondary phase with a B2-type Ti0.6Zr0.4Ni cubic structure. Rietveld analysis revealed that the secondary phase increased with an increase in the x value. The hydrogen storage capacity of the HEAs was lower than that of the alloy with x = 0 because of an increase in the B2-type Ti0.6Zr0.4Ni phase, whereas the change in enthalpy of hydride formation (|ΔH|) decreased with increasing x, leading to the instability of hydrides. The alkaline treatment was performed by immersing HEA powders or electrode in a 6 M KOH aqueous solution at 378 K for 2 h. The Zr0.2Ti0.2Ni0.2Cr0.2Mn0.2 alloy surface changed to a porous and rough structure, and a ZrO2 passive thin layer on their surface, which is replaced by NiO or Ni(OH)2 after the alkaline treatment. The charge–discharge tests conducted using the HEA negative electrodes for Ni-MH batteries depict that the discharge capacity increased with an increase in x, and the highest discharge capacity was 368 mAh g‐1 at x = 0.075 after the alkaline treatment. On increasing the x value, the high-rate dischargeability and cycle performance were also enhanced.

Effect of Co substitution on hydrogenation behavior of GdNi3-xCox (x = 0, 0.2, 1.0) and crystal structure of its hydride phases

The effect of substituting Co for Ni in GdNi3 on the hydrogenation properties and phase transformation during the hydrogen absorption–desorption process of GdNi3-xCox (x = 0, 0.2, 1.0) was investigated using P–C isotherms and X-ray diffraction analysis (XRD). GdNi3 showed a residual hydrogen content of 0.6 H/M after the first desorption process. The maximum hydrogen capacity of GdNi3 was 1.0 H/M, while the reversible hydrogen capacity decreased to 0.4 H/M because of the residual hydrogen. The reversible hydrogen capacity was improved to 1.0 H/M in GdNi2.0Co1.0, and two plateaus were observed in the absorption–desorption process. The crystal structures of the full hydride phases GdNi3H3.8 and GdNi2.8Co0.2H3.8 could not be determined because of the heavy peak broadening in the XRD pattern, while the PuNi3-type structure of the original alloy was retained in the full hydride phase GdNi2.0Co1.0H3.6. The retention rates of GdNi3 and GdNi2.0Co1.0 at 100 cycles were 75% and 92%, respectively. The cyclic properties of GdNi2.0Co1.0, up to 100 cycles, favorably compared with those of LaNi5, which was found to be related to the small lattice strain formed during the first hydrogen absorption process.

Graphene and Carbon Nanotubes Fibrous Composite Decorated with PdMg Alloy Nanoparticles with Enhanced Absorption-Desorption Kinetics for Hydrogen Storage Application.

We describe a graphene and fibrous multiwall carbon nanotubes (f-MWCNT) composite film prepared by plasma-enhanced chemical vapor deposition for use as a suitable and possible candidate of hydrogen storage materials. A high storage capacity of 5.53 wt% has been obtained with improved kinetics. The addition of binary PdMg alloy nanoparticles to the surface of graphene-fibrous nanotubes composite films raised the storage capacity by 53% compared to the film without PdMg decorated nanoparticles. Additionally, the graphene/f-MWCNT composite film decorated with PdMg nanoparticles exhibited an enhanced hydrogen absorption–desorption kinetics. The fibrous structure of the MWCNTs, alongside graphene sheets within the film, creates an enormous active region site for hydrogen reaction. The addition of PdMg nanoparticles enhanced the reaction kinetics due to the catalytic nature of Pd, and increased the hydrogen content due to the high absorption capacity of Mg nanoparticles. The combination of Pd and Mg in a binary alloy nanoparticle enhanced the hydrogen capacity and absorption–desorption kinetics.

Hydrogen occupation in Ti4M2Oy compounds (M = Fe, Co, Ni, Cu, and y = 0, 1) and their hydrogen storage characteristics

The hydrogen sorption properties of Ti4M2Oy compounds (M = Fe, Co, Ni, Cu or their mixture and y = 0, 1) were studied to assess their utility as room-temperature hydrogen storage materials. The main parameter controlling the hydrogen sorption property is the energy of hydrogen incorporation into the compounds, which was evaluated by density functional theory total-energy calculations. Energetics provides basic information on the sequence of hydrogen filling into the available interstitial sites, and when the minimum H–H distance is also considered, a more sensible prediction of the site occupation becomes possible. The calculation results suggested that between Ti4Fe2O and Ti4Ni2O, Ti4Ni2O was a better candidate for room-temperature hydrogen storage. An almost-single-phase Ti4Ni2O compound was successfully synthesized starting from TiO2, Ti, and Ni using the arc-melting method. Ti4Ni2O stored 1.3 wt% of hydrogen under 7 MPa of H2 pressure at 30 °C. The storage properties of Ti4Ni2O were modified by the partial substitution of Fe, Co, and Cu for Ni. The partial substitution did not improve the usable capacity, but the hydrogen absorption–desorption characteristics demonstrated that the equilibrium hydrogen pressure could be precisely controlled via composition change.

Hydrogen absorption-desorption cycle decay mechanism of palladium nanoparticle decorated nitrogen doped graphene

As a hydrogen storage material, palladium nanoparticle decorated nitrogen doped graphene (Pd/N-rGO) has drawn much attention owing to its high absorption capacity at moderate conditions. However, its hydrogen absorption-desorption cycle performance, which is essential for their practical application, has been rarely studied. In this paper, a simple and convenient high temperature thermal reduction method was used to synthesize nitrogen-doped graphene decorated with Pd nanoparticles (Pd/N-rGO). Taken it as a representative, the hydrogen absorption-desorption cycle performance of Pd/N-rGO was investigated. The results showed that after three cycles the hydrogen storage capacity dropped from 2.9 ​wt% to 0.8 ​wt% at 25 ​°C and 4 ​MPa pressure. It was found that the palladium nanoparticles shed from Pd/N-RGO sheet after cycle performance test, and then agglomerated. These phenomena will weaken the hydrogen spillover effect, leading to the decrease of hydrogen storage capacity. Meanwhile, decreased defects reduce the hydrogen absorption sites, which will thus deteriorate the hydrogen storage capacity.

Comparative investigation on the hydrogen absorption-desorption characteristics of R2MgNi9 (R = Nd, Gd and Er) compounds

To understand the effect of rare earth atomic radius on hydrogen storage properties of layered R-Mg-Ni compounds, the hydrogen absorption-desorption characteristics of R2MgNi9 (R = Nd, Gd and Er) compounds have been investigated in this work. As the radii of rare earth atoms decrease from Nd to Gd and Er, the lattice parameters (a and c) decrease gradually, leading to the decreases in dehydriding enthalpies and hydrogen capacities. Additionally, the cycle stabilities also decrease from Nd2MgNi9 to Gd2MgNi9 and Er2MgNi9 because their lattice strains increase after 50 cycles.

Hydrogen sorption properties of new magnesium intermetallic compounds with MgSnCu4 type structure

A statistical theory of the MgCeCo4–H2 system has been developed for hydrogenation and phase transitions under pressure. The free energy value is calculated. The equation of thermodynamic equilibrium is obtained. The temperature of the order-disorder phase transition is estimated. Isotherms and Isoplethes of hydrogen absorption-desorption are constructed. The possibility of a hysteresis effect is established. The temperature dependence of the hydrogen solubility is found taking into account the phase transition configuration heat capacity. The calculated and experimental graphs of the sorption isotherm are of a similar nature.

Influence of carbon catalysts on the improvement of hydrogen storage properties in a body-centered cubic solid solution alloy

Body-centered cubic (BCC) alloys are considered as promising materials for hydrogen storage with high theoretical storage capacity (H/M ratio of 2). Nonetheless, they often suffer from sluggish kinetics of hydrogen absorption and high hydrogen desorption temperature. Carbon materials are efficient hydrogenation catalysts, however, their influence on the hydrogen storage properties of BCC alloy has not been comprehensively studied. Therefore, in this paper, composites obtained by milling of carbon catalysts (carbon nanotubes, mesoporous carbon, carbon nanofibers, diamond powder, graphite, fullerene) and BCC alloy (Ti1.5V0.5) were extensively studied in the non-hydrogenated and hydrogenated state. The structure and microstructure of the obtained materials were studied by scanning and transmission electron microscopes, X-ray diffraction (XRD), and Raman spectroscopy. XRD and Raman measurements showed that BCC alloy and carbon structures were in most cases intact after the composite synthesis. The hydrogenation/dehydrogenation studies showed that all of the used carbon catalysts significantly improve the hydrogenation kinetics, reduce the activation energy of the dehydrogenation process and decrease the dehydrogenation temperature (by nearly 100 K). The superior kinetic properties were measured for the composite with 5 wt % of fullerene that absorbs 3.3 wt % of hydrogen within 1 min at room temperature.

Facile synthesis of a Ni3S2@C composite using cation exchange resin as an efficient catalyst to improve the kinetic properties of MgH2

Carbon materials have excellent catalytic effects on the hydrogen storage performance of MgH2. Here, carbon-supported Ni3S2 (denoted as Ni3S2@C) was synthesized by a facile chemical route using ion exchange resin and nickel acetate tetrahydrate as raw materials and then introduced to improve the hydrogen storage properties of MgH2. The results indicated the addition of 10 wt.% Ni3S2@C prepared by macroporous ion exchange resin can effectively improve the hydrogenation/dehydrogenation kinetic properties of MgH2. At 100 °C, the dehydrogenated MgH2-Ni3S2@C-4 composite could absorb 5.68 wt.% H2. Additionally, the rehydrogenated MgH2-Ni3S2@C-4 sample could release 6.35 wt.% H2 at 275 °C. The dehydrogenation/hydrogenation enthalpy changes of MgH2-Ni3S2@C-4 were calculated to be 78.5 kJ mol−1/−74.7 kJ mol−1, i.e., 11.0 kJ mol−1/7.3 kJ mol−1 lower than those of MgH2. The improvement in the kinetic properties of MgH2 was ascribed to the multi-phase catalytic action of C, Mg2Ni, and MgS, which were formed by the reaction between Ni3S2 contained in the Ni3S2@C catalyst and Mg during the first hydrogen absorption–desorption process.

Hydrogenation characteristics of Ce2Ni7-type La2Co7 and its phase transformation during hydrogen absorption–desorption processes

We have investigated the crystal structure and hydrogenation properties of La2Co7 with a Ce2Ni7-type structure by X-ray diffraction (XRD) and P–C isotherm (pressure composition isotherm) analyses. The maximum hydrogen capacity reached 0.79 ​H/M (1.04 mass%). After the first full desorption, 0.50 ​H/M (0.66 mass%) of hydrogen remained in the sample, and the reversible hydrogen capacity decreased to 0.24 ​H/M (0.32 mass%) in the second absorption–desorption cycle. Three plateaus were observed in the first absorption cycle, and the crystal structures of the two hydride phases were identified. A Ce2Ni7-type structure (space group: P63/mmc) was identified for La2Co7H2.8 (I), which is similar to that of La2Co7. La2Co7H5.0 (II) was identified to have a hexagonal structure with a lower symmetry (space group: P-62c). The lattice parameters are a ​= ​0.50428(9) nm and c ​= ​2.9861(4) nm, and the expansions of a and c relative to the lattice parameters of La2Co7 are −1.9 and 21.3%, respectively, indicating anisotropic expansion. For La2Co7H7.2 (III, full hydride phase), severe peak broadening was observed in the XRD pattern, and it was difficult to construct a suitable structural model. The crystal structure transformation occurred in the order of a hexagonal Ce2Ni7-type structure (La2Co7) → the same Ce2Ni7-type structure (La2Co7H2.8) → a hexagonal structure with a lower symmetry (La2Co7H5.0) → an unknown structure (La2Co7H7.2).

Effect of Ti-based nanosized additives on the hydrogen storage properties of MgH2

MgH2-based nanocomposites were synthesized by high-energy reactive ball milling (RBM) of Mg powder with 0.5–5 mol% of various catalytic additives (nano-Ti, nano-TiO2, and Ti4Fe2Ox suboxide powders) in hydrogen. The additives were shown to facilitate hydrogenation of magnesium during RBM and substantially improve its hydrogen absorption-desorption kinetics. X-ray diffraction analysis showed the formation of nanocrystalline MgH2 and hydrogenation of nano-Ti and Ti4Fe2Ox. The possible reduction of TiO2 during RBM in hydrogen was not observed, which is in agreement with lower hydrogenation capacity of the corresponding composite, 5.7 wt% for Mg + 5 mol% nano-TiO2 compared to 6.5 wt% for Mg + 5 mol% nano-Ti. Hydrogen desorption from the as-prepared composites was studied by Thermal Desorption Spectroscopy (TDS) in vacuum. A significant lowering of the hydrogen desorption temperature of MgH2 by 30–90 °C in the presence of the additives is associated with lowering activation energy from 146 kJ/mol for nanosized MgH2 down to 74 and 67 kJ/mol for MgH2 modified with nano-TiO2 and Ti4Fe2O0.3 additives, respectively. After hydrogen desorption at 300–350 °C, these materials are able to absorb hydrogen even at room temperature. It is shown that nano-structuring and addition of Ti-based catalysts do not decrease thermodynamic stability of MgH2. The thermodynamic parameters, obtained from hydrogen desorption isotherms for the Mg–Ti4Fe2O0.3 nanocomposite, ΔHdes = 76 kJ/mol H2 and ΔSdes = 138 J/K·mol H2, correspond to the reported literature values for pure polycrystalline MgH2. Hydrogen absorption-desorption characteristics of the composites with nano-Ti remain stable during at least 25 cycles, while a gradual decay of the reversible hydrogen capacity occurred in the case of TiO2 and Ti4Fe2Ox additives. Cycling stability of Mg/Ti4Fe2Ox was substantially improved by introduction of 3 wt% graphite into the composite.

Crystal structure of intermetallic compound Y5Co19 and its hydride phases

Y–Co intermetallic compounds and their hydrides were investigated as magnetic materials, but the hydrogenation of these alloys was not observed. We established the existence of Y5Co19 in the phase diagrams of the Y–Co system. Y5Co19, an intermetallic compound, was synthesized and its crystal structure was determined by the Rietveld refinement of X-ray diffraction (XRD) data. The structural model of Y5Co19 is a Ce5Co19-type model with lattice parameters a = 0.4994 (1) nm and c = 4.800 (1) nm. The crystal structure of the original alloy and its hydride phase is closely related to the hydrogen absorption–desorption property. The hydrogen capacity of Y5Co19 was 0.63 H/M, while two plateaus were observed in the P–C isotherm. We discovered two hydride phases: Y5Co19H3.8 (phase I) and Y5Co19H14.9 (phase II), and the structural model of these phases (I and II) was Ce5Co19-type, which was the same as the original alloy. The unit cell of phase I showed an expansion of 3.9% only along the c-axis from the original alloy, whereas that of phase II indicated an expansion along the a- and c-axes. Additionally, a close isotropic expansion was observed in phase II.

Synergetic effect of multiple phases on hydrogen desorption kinetics and cycle durability in ball milled MgH2–PrF3–Al–Ni composite

A new MgH2–PrF3–Al–Ni composite was prepared by ball milling under hydrogen atmosphere. After initial dehydrogenation and rehydrogenation, Pr3Al11, MgF2, PrH3 and Mg2NiH4 nanoparticles formed accompanying the main phase MgH2. The hydrogen absorption-desorption properties were measured by using a Sieverts-type apparatus. The results showed that the MgH2–PrF3–Al–Ni composite improved cycle stability and enhanced hydrogen desorption kinetics. The improvement of hydrogen absorption-desorption properties is ascribed to the synergetic effect of the in situ formed Pr3Al11, MgF2, PrH3 and Mg2NiH4 nanoparticles. This work provides an important inspiration for the improvement of hydrogen storage properties in Mg-based materials.

Stress reduction in a hydride container by the addition of a glidant agent

Hydrogen absorbing materials, such as metal hydrides, present a possible solution for hydrogen storage. During the absorption process these materials swell, which can put the mechanical integrity of its container at risk. One possibility is to increase the flowability of the absorbing material, usually a fine cohesive powder, so that it can rearrange within its container during the swelling stage. In this work, we study if this rearrangement could be improved by the addition of Aerosil, a type of colloidal silica widely used as glidant agent. The walls of a stainless steel reactor are instrumented with strain gauges to measure the accumulation of stresses due to hydrogen absorption-desorption cycles. We explore the container filled with pure LaNi5 absorbing material previously activated, so as with different Aerosil-added proportions. Results show that Aerosil allows avoiding stress build-up, for all glidant concentrations used in present study.

Stress measurement of MlNi4.5Cr0·45Mn0.05 alloy during hydrogen absorption-desorption process in a cylindrical reactor

Hydrogen stored in a solid state form of metal hydrides offers a safe and efficient storage technique for hydrogen application. In a closed metal hydride tank, stresses may occur on the tank wall due to hydride expansion during hydrogen absorption process. In the present investigation, a novel testing system for stress evolution of MlNi4.5Cr0.45Mn0.05 alloy in a closed cylindrical reactor during hydrogen absorption-desorption process was built. The results show that considerable swelling stress is developed on the inner reactor wall during activation process though a high free space of 45% is presented. Increasing hydrogen charging pressure and alloy loading fraction increase the as-generated swelling stress. The metal hydride particle expansion caused by hydrogen absorption is the intrinsic factor for swelling stress evolution. The presence of particle agglomerate in a closed tank in which its expansion is constrained is responsible for the observed swelling stress accumulation.

Synergistic catalytic effects of ZIF-67 and transition metals (Ni, Cu, Pd, and Nb) on hydrogen storage properties of magnesium

MgTM/ZIF-67 nanocomposites were prepared by the deposition-reduction method using ZIF-67, MgCl2, and TMClx (TM = Ni, Cu, Pd, Nb) as raw materials. The dehydrogenation activation energies of MgTM/ZIF-67 (TM = Ni, Cu, Pd, Nb) nanocomposites were calculated to be 115.4 kJ mol−1 H2, 115.7 kJ mol−1 H2, 113.6 kJ mol−1 H2, and 75.8 kJ mol−1 H2, respectively; hence, the MgNb/ZIF-67 nanocomposite manifested the best comprehensive hydrogen storage performance. The hydrogen storage capacity of the MgNb/ZIF-67 nanocomposite was hardly attenuated after the 100th hydrogen absorption-desorption cycle. The dehydrogenated enthalpies of MgH2 and CoMg2H5 in MgNb/ZIF-67 hydride were calculated to be 72.4 kJ mol−1 H2 and 81.0 kJ mol−1 H2, respectively, which were lower than those of additive-free MgH2 and Mg/ZIF-67. The improved hydrogen storage properties of MgNb/ZIF-67 can be ascribed to the CoMg2–Mg(Nb) core-shell structure and the catalytic effects of NbH and niobium oxide nanocrystals.