Initial Desorption Temperature Research Articles

Microstructure and hydrogen storage properties of the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys

Rare earth elements have excellent catalytic effects on improving hydrogen storage properties of the Mg2Ni-based alloys. This study used a small amount of Y to substitute Mg partially in Mg2Ni0.9Co0.1 and characterized and discussed the effects of Y on the solidification and de-/hydrogenation behaviors. The Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) hydrogen storage alloys were prepared using a metallurgy method. The phase composition of the alloys was studied using X-ray diffraction (XRD). Additionally, their microstructure and chemical composition were studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The hydrogen absorption and desorption properties of the alloys were studied using pressure-composition isotherms and differential scanning calorimetric (DSC) measurements. The structure of the as-cast Mg2Ni0.9Co0.1 alloy was composed of the peritectic Mg2Ni, eutectic Mg–Mg2Ni, and a small amount of pre-precipitated Mg–Ni–Co ternary phases, and was converted into the Mg2NiH4, Mg2Ni0.9Co0.1H4, and MgH2 phases after hydrogen absorption. Furthermore, the XRD patterns of the alloys showed the MgYNi4 phase and a trace amount of the Y2O3 phase along with the Mg and Mg2Ni phases after the addition of Y. After hydrogen absorption, the phase of the alloys was composed of the Mg2NiH4, MgH2, MgYNi4, YH3, Y2O3, and Mg2NiH0.3 phases. With the increase of Y addition, the area ratios of the peritectic Mg2Ni matrix phase in the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys gradually decreased until they disappeared. However, the eutectic structure gradually increased, and the microstructures of the alloys were obviously refined. The addition of Y improves the activation performance of the alloys. The alloy only needed one cycle of de-/hydrogenation to complete the activation for x = 0.4. The DSC curves showed that the initial dehydrogenation temperatures of Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 were 200 and 156 °C, respectively. The desorption activation energies of the hydrides of the Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 alloys calculated using the Kissinger method were 94.7 and 56.5 kJ/mol, respectively. Moreover, the addition of Y reduced the initial desorption temperature of the alloys and improved their kinetic properties.

Enhancing hydrogen storage performance of MgH2 through the addition of BaMnO3 synthesized via solid-state method

Currently, magnesium hydride (MgH2) as a solid-state hydrogen storage material has become the subject of major research owing to its good reversibility, large hydrogen storage capacity (7.6 wt%) and affordability. However, MgH2 has a high decomposition temperature (>400 °C) and slow desorption and absorption kinetics. In this work, BaMnO3 was synthesized using the solid-state method and was used as an additive to overcome the drawbacks of MgH2. Interestingly, after adding 10 wt% of BaMnO3, the initial desorption temperature of MgH2 decreased to 282 °C, which was 138 °C lower than that of pure MgH2 and 61 °C lower than that of milled MgH2. For absorption kinetics, at 250 °C in 2 min, 10 wt% of BaMnO3-doped MgH2 absorbed 5.22 wt% of H2 compared to milled MgH2 (3.48 wt%). Conversely, the desorption kinetics also demonstrated that 10 wt% of BaMnO3-doped MgH2 samples desorbed 5.36 wt% of H2 at 300 °C within 1 h whereas milled MgH2 only released less than 0.32 wt% of H2. The activation energy was lowered by 45 kJ/mol compared to that of MgH2 after the addition of 10 wt% of BaMnO3. Further analyzed by using XRD revealed that the formation of Mg0·9Mn0·1O, Mn3O4 and Ba or Ba-containing enhanced the performance of MgH2.

Catalytic effect of bamboo-like carbon nanotubes loaded with NiFe nanoparticles on hydrogen storage properties of MgH2

Catalyst doping modification has become an important strategy to solve the high desorption temperature and sluggish kinetics issues of magnesium hydride (MgH2) for further commercial application. Herein, we report a novel strategy by exploiting a catalyst with the “magnesophilic” transition metal and “magnesiphobic” carbon material to construct a MgH2-catalysts-carbon layer hydrogen storage material, where the bimetallic NiFe nanoparticles are supported atop the bamboo-like carbon nanotubes (NiFe@CNT) via calcination. The experimental results show that the built MgH2-NiFe@CNT composite can absorb 4.06 and 3.25 wt% H2 at 373 and 348 K, respectively, while the milled-MgH2 almost no longer absorbs H2 and takes only 0.82 wt% even at 423 K. More importantly, the initial desorption temperature of the MgH2-NiFe@CNT composite reduces to 498 K by 122 K in contrast to the milled-MgH2, and the dehydrogenation activation energy decreases from 151.8 to 49.7 kJ mol−1. Ex situ structural characterization and theoretical calculation show that the synergistic effects of the “hydrogen pump” role of Mg2Ni/Mg2NiH4 and “hydrogen gateway” role of α-Fe, as well as the good dispersion function of carbon nanotubes generated in situ from the NiFe@CNT, contribute the excellent hydrogen storage properties of the MgH2-NiFe@CNT composite. This study provides new insights into the modification of MgH2 by carbon-supported transition metal catalysts.

Enhanced hydrogen storage properties of NaAlH4 with the addition of CoTiO3 synthesised via a solid-state method

CoTiO3 that was synthesised via the solid-state method was effective in ameliorating the desorption behaviour of NaAlH4. The initial desorption temperature of NaAlH4 catalysed by different weight percentage of CoTiO3 (5 wt%, 10 wt%, 15 wt% and 20 wt%) was dramatically decreased to around 130–160 °C for the first desorption stage and decreased to around 182–198 °C for the second desorption stage, which is lower than milled NaAlH4. The composite sample also exhibits 15–18 times faster desorption kinetics at 150 °C where the NaAlH4-CoTiO3 composite could release 3.0–3.7 wt% of H2 in 60 min but milled NaAlH4 only could release 0.2 wt% H2 in the same time duration. The activation energies for the two-desorption stage of NaAlH4 was downshifted to 85.5 and 91.6 kJ/mol, lowered by 30.7 and 35.5 kJ/mol than milled NaAlH4, respectively. The beneficial catalytic effect of CoTiO3 can be attributed to the in-situ formation of Al-Co and Al-Ti alloys after the desorption process of the NaAlH4-CoTiO3 system. These findings pave the way for the development of highly effective catalysts for NaAlH4 as a favourable material for hydrogen storage.

Improved Dehydrogenation Properties of LiAlH4 by Addition of Nanosized CoTiO3.

Despite the application of lithium aluminium hydride (LiAlH4) being hindered by its sluggish desorption kinetics and unfavourable reversibility, LiAlH4 has received special attention as a promising solid-state hydrogen storage material due to its hydrogen storage capacity (10.5 wt.%). In this work, investigated for the first time was the effect of the nanosized cobalt titanate (CoTiO3) which was synthesised via a solid-state method on the desorption behaviour of LiAlH4. Superior desorption behaviour of LiAlH4 was attained with the presence of a CoTiO3 additive. By means of the addition of 5, 10, 15 and 20 wt.% of CoTiO3, the initial desorption temperature of LiAlH4 for the first stage was reduced to around 115-120 °C and the second desorption stage was reduced to around 144-150 °C, much lower than for undoped LiAlH4. The LiAlH4-CoTiO3 sample also presents outstanding desorption kinetics behaviour, desorbing hydrogen 30-35 times faster than undoped LiAlH4. The LiAlH4-CoTiO3 sample could desorb 3.0-3.5 wt.% H2 in 30 min, while the commercial and milled LiAlH4 desorbs <0.1 wt.% H2. The apparent activation energy of the LiAlH4-CoTiO3 sample based on the Kissinger analysis was decreased to 75.2 and 91.8 kJ/mol for the first and second desorption stage, respectively, lower by 28.0 and 24.9 kJ/mol than undoped LiAlH4. The LiAlH4-CoTiO3 sample presents uniform and smaller particle size distribution compared to undoped LiAlH4, which is irregular in shape with some agglomerations. The experimental results suggest that the CoTiO3 additive promoted notable advancements in the desorption performance of LiAlH4 through the in situ-formed AlTi and amorphous Co or Co-containing active species that were generated during the desorption process.

Enhanced de-/hydrogenation kinetics of a hyper-eutectic Mg85Ni15-Ag alloy facilitated by Ag dissolving in Mg2Ni

In order to accelerate the hydrogen absorption and desorption rates of hyper-eutectic Mg-Ni alloy, Mg 85 Ni 15- x Ag x ( x = 0, 0.2, 0.4, 0.6) alloys were prepared and the results show that fishbone eutectic was formed without change of phase composition. It was found that Ag atoms were dissolved in fishbone eutectic Mg 2 Ni and the average cell parameters of Mg 2 Ni increase with the increase of Ag content. Owing to adjusting lattice parameters, the hydrogen absorption and desorption rates of Mg 85 Ni 14.8 Ag 0.2 alloy are significantly improved. About 4.47 wt% hydrogen is absorbed at 275 ℃ only in 1 min, with the maximum capacity of 5.84 wt% in 60 min. The Mg 85 Ni 15- x Ag x ( x = 0.2, 0.4, 0.6) hydrides can be completely dehydrogenated within 10 min at 275 ℃. The corresponding activation energies for dehydrogenation are determined to be 80.4, 97.1 and 97.8 kJ/mol, respectively, which are lower than 117.8 kJ/mol of Mg 85 Ni 15 . The onset dehydrogenation temperature of Mg 85 Ni 14.8 Ag 0.2 hydride is reduced to 201 ℃, which is much lower than 220 ℃ of the Mg 85 Ni 15 hydride. The dissolving of Ag in Mg 2 Ni leads to a lattice expansion, which facilitates the diffusion for hydrogen atoms and decrease the energy barrier required for nucleation of Mg/Mg 2 Ni. As a result, the hydrogen de-/absorption rates were obvious accelerated and the onset dehydrogenation temperature was decreased. • The lattice size of Mg2Ni was regulated by doping Ag. • Hydrogen storage capacity of Mg85Ni14.8Ag0.2 alloy reaches 5.84 wt% at 275 ℃. • The Ea value for decomposition of Mg85Ni14.8Ag0.2 hydride decreases to 80.4 kJ/mol. • Addition of Ag reduces the initial desorption temperature of Mg85Ni15 hydrides.

Dehydrogenation of Metal Hydride Reactor-Phase Change Materials Coupled with Light-Duty Fuel Cell Vehicles

The popularity of using phase change materials (PCMs) for heat storage and recovery of metal hydrides’ reaction has grown tremendously. However, a fundamental study of the coupling of such a system with a low-temperature PEM (polymer electrolyte membrane) fuel cell is still lacking. This work presents a numerical investigation of the dehydrogenation performance of a metal hydride reactor (MHR)-PCM system coupled with a fuel cell. It is shown that to supply the fuel cell with a constant H2 flow rate, the PCM properties need to be in an optimized range. The effects of some design parameters (PCM freezing point, the initial desorption temperature, the nature and the size of the PCM) on the dehydrogenation performance of MHR-PCM system are discussed in detail. The results showed that the MHR-PCM could supply hydrogen at 12 NL/min only for 20 min maximum due to the significant endothermic effect occurring in the MHR. However, reducing the requested H2 flowrate to 5.5 NL/min, the hydrogen desorption to a fuel cell is prolonged to 79 min. Moreover, this system can accommodate different PCMs such as paraffin and salt hydrates for comparable performance. This study demonstrates the ability of MHR-PCM systems to be used as range extenders in light-duty fuel cell vehicles.

The Improvement in Hydrogen Storage Performance of MgH2 Enabled by Multilayer Ti3C2.

MgH2 has become a hot spot in the research of hydrogen storage materials, due to its high theoretical hydrogen storage capacity. However, the poor kinetics and thermodynamic properties of hydrogen absorption and desorption seriously hinder the development of this material. Ti-based materials can lead to good effects in terms of reducing the temperature of MgH2 in hydrogen absorption and desorption. MXene is a novel two-dimensional transition metal carbide or carbonitride similar in structure to graphene. Ti3C2 is one of the earliest and most widely used MXenes. Single-layer Ti3C2 can only exist in solution; in comparison, multilayer Ti3C2 (ML-Ti3C2) also exists as a solid powder. Thus, ML-Ti3C2 can be easily composited with MgH2. The MgH2+ML-Ti3C2 composite hydrogen storage system was successfully synthesized by ball milling. The experimental results show that the initial desorption temperature of MgH2-6 wt.% ML-Ti3C2 is reduced to 142 °C with a capacity of 6.56 wt.%. The Ea of hydrogen desorption in the MgH2-6 wt.% ML-Ti3C2 hydrogen storage system is approximately 99 kJ/mol, which is 35.3% lower than that of pristine MgH2. The enhancement of kinetics in hydrogen absorption and desorption by ML-Ti3C2 can be attributed to two synergistic effects: one is that Ti facilitates the easier dissociation or recombination of hydrogen molecules, while the other is that electron transfer generated by multivalent Ti promotes the easier conversion of hydrogen. These findings help to guide the hydrogen storage properties of metal hydrides doped with MXene.

Composition dependent hydrogen storage performance and desorption factors of Mg–Ce based alloys

The widespread application of Mg as a hydrogen storage material has been limited by its slow absorption and desorption kinetics at moderate temperatures. Aiming at improving the de-/absorption kinetics of Mg-based alloys by in situ formed catalysts and understanding the desorption factors, Mg–Ce and Mg–Ce–Ni alloys with different Ce contents are prepared. The phase components, microstructure and hydrogen storage properties have been carefully investigated. It is shown that an 18R-type long-period stacking ordered (LPSO) phase is formed in as-melt Mg–Ce–Ni ternary alloy together with random stacking faults. Abundant in situ formed CeH2.73 particles with particle size less than 100 nm are observed on the matrix after hydrogenation. It is found in isothermal hydrogenation and dehydrogenation kinetic curves that Ni significantly favors desorption process, while Ce is more conducive to absorption. After partial dehydrogenation of Mg–Ce binary alloy, the initial desorption temperature decreases significantly when desorbing again. The primary-formed Mg phase on the surface of MgH2 accounts for the improved desorption performance.

Dehybridization effect in improved dehydrogenation of LiAlH4 by doping with two-dimensional Ti3C2

Lowering the thermodynamic and kinetic barriers for dehydrogenation of high-capacity hydrides has been a key challenge for the realization of practical hydrogen energy. One of the most efficient strategies is doping hydrides with catalysis while nanosizing the composites. Although numerous catalytic additives have been investigated, more efficient dopants are still under exploration, and the underling mechanism of catalysis is highly desirable. In this study, a two-dimensional (2D) layered metal carbide, Ti3C2, was doped to improve the dehydrogenation performance of LiAlH4. The results show that, by doping 5 wt% of Ti3C2, the initial desorption temperature of LiAlH4 decreased significantly from 180.1 to 58.6 with 6.5 wt% of hydrogen release. Approximately 5.5 wt% of hydrogen was liberated from the LiAlH4+5 wt% Ti3C2 sample at 200 °C within 35 min. Combining density functional theory calculations, we reveal that contact of 2D Ti3C2 significantly decreases the desorption energy barrier of Al–H bonding in LiAlH4 and accelerates the breakdown of Al–H bonding through the interfacial charge transfer and the dehybridization of the Al–H cluster.

Time-integrated thermal desorption for quantitative SIFT-MS analyses of atmospheric monoterpenes.

A new time-integrated thermal desorption technique has been developed that can be used with selected ion flow tube mass spectrometry, TI-TD/SIFT-MS, for off-line quantitative analyses of VOCs accumulated onto sorbents. Using a slow desorption temperature ramp, the absolute amounts of desorbed compounds can be quantified in real time by SIFT-MS and constitutional isomers can be separated. To facilitate application of this technique to environmental atmospheric monitoring, method parameters were optimised for quantification of the three common atmospheric monoterpenes: β-pinene, R-limonene and 3-carene. Three sorbent types, Tenax TA, Tenax GR and Porapak Q, were tested under 26 different desorption conditions determined by the "design of experiment", DOE, systematic approach. The optimal combination of type of sorbent, bed length, sampling flow rate, sample volume and the initial desorption temperature was determined from the experimental results by ANOVA. It was found that Porapak Q exhibited better efficiency of sample collection and further extraction for total monoterpene concentration measurements. On the other hand, Tenax GR or TA enabled separation of all three monoterpenes. The results of this laboratory study were tested with the sample accumulated from a branch of a Pinus nigra tree. Graphical abstract.

Enhanced Hydrogen Storage Properties and Reversibility of LiBH4 Confined in Two-Dimensional Ti3C2.

LiBH4 is of particular interest as one of the most promising materials for solid-state hydrogen storage. Herein, LiBH4 is confined into a novel two-dimensional layered Ti3C2 MXene through a facile impregnation method for the first time to improve its hydrogen storage performance. The initial desorption temperature of LiBH4 is significantly reduced, and the de-/rehydrogenation kinetics are remarkably enhanced. It is found that the initial desorption temperature of LiBH4@2Ti3C2 hybrid decreases to 172.6 °C and releases 9.6 wt % hydrogen at 380 °C within 1 h, whereas pristine LiBH4 only releases 3.2 wt % hydrogen under identical conditions. More importantly, the dehydrogenated products can partially rehydrogenate at 300 °C and under 95 bar H2. The nanoconfined effect caused by unique layered structure of Ti3C2 can hinder the particles growth and agglomeration of LiBH4. Meanwhile, Ti3C2 could possess superior effect to destabilize LiBH4. The synergetic effect of destabilization and nanoconfinement contributes to the remarkably lowered desorption temperature and improved de-/rehydrogenation kinetics.

Effect of the hierarchical Co@C nanoflowers on the hydrogen storage properties of MgH2

A hierarchical Co@C nanoflowers are synthesized via a simple route based on a low-temperature solid-phase reaction. The as-prepared hierarchical Co@C nanoflowers have an enhanced catalytic activity on the hydrogen storage properties of MgH2 and thermodynamics and kinetics properties of the MgH2Co@C composite are systematically researched. It is found that the initial desorption temperature of the MgH2Co@C is about 201 °C, 99 °C lower compared to MgH2. And the MgH2Co@C material can release 5.74 wt % within 30 min and 6.08 wt % H2 within 60 min at 300 °C. Whereas, pure as-milled MgH2 only can release 0.37 wt % within 30 min and 1.20 wt % hydrogen within 60 min at the same temperature. Meanwhile, the hydrogen absorption amount of MgH2Co@C achieve 5.96 wt% within 10 min at 300 °C, and the maximum hydrogen absorption amount reach 6.16 wt% within 20 min. In addition, the introduction of hierarchical Co@C nanoflowers also reduces the activation energy (Ea) 46 kJ mol−1, which exhibits a promoted kinetics. In addition, the relative hydrogen desorption mechanism of MgH2Co@C has also been discussed.

2Mg-Fe Alloy Processed by Hot Extrusion: Influence of Particle Size and Extrusion Reduction Ratio on Hydrogenation Properties

Samples of a 2Mg-Fe (at.%) mixture were produced by high energy ball-milling (HEBM) with ball to powder ratio = 20:1, in an argon gas atmosphere, in 190 ml vials (sample-1) to produce powders and in 300 ml vials (sample-2) to produce plates. Both samples were cold-pressed into preforms. The preforms were then extruded at 300°C at a ram speed of 1mm/min., with the following extrusion ratios: sample-1 at 3/1 to ensure porosity and sample-2 at 5/1 to increase the adhesion of the plates. The resulting bulks from samples 1 and 2 were hydrogenated for 24h in a reactor under 15 bar of H2to produce the Mg2FeH6complex hydride, and at 11 bar of H2to produce both the complex hydride and MgH2hydride. In addition, sample-1 was severely temperature-hydrogen cycled to verify its microstructural stability and the influence of grain size on the sorption properties. XRD patterns showed Mg(hc), Fe(ccc) and Mg2FeH6in both samples, and sample-2 also contained MgH2and MgO (attributed to processing contamination). DSC results demonstrated that the initial desorption temperature of sample-1 was lower than that of sample-2. However, sample-2 showed faster desorption kinetics, presenting a desorption peak about 73°C below that of sample-1. This could be attributed to the activation/catalyst effect of the MgH2hydride. The improvement in sorption properties was attributed mainly to porosity and to the type of employed catalysts.

Hydrogen desorption behavior of vanadium borohydride synthesized by modified mechano-chemical process

The vanadium borohydride was synthesized by a mechano-chemical milling method and its hydrogen desorption performance was evaluated. The effect of cooling during milling process on the hydrogen desorption behavior was also investigated. Nearly pure hydrogen was detected using a mass spectrometer coupled with a simultaneous thermal analyzer. Thermogravimetric method was conducted to determine the initial desorption temperature and the amount of hydrogen released from the hydride. The initial desorption temperature of vanadium borohydride was found below 100 °C, with an enthalpy change of 25.4 kJ/mol V(BH 4) 3. The amount of hydrogen released from the hydride prepared by milling but without cooling was 0.25 wt%, while that prepared with controlled cooling at 20 °C was 1 wt%. A beneficial effect of enhanced hydrogen release to 2.2 wt% from borohydride was found if multi-walled carbon nanotubes (MWCNTs) were added as an additive.

Hydrogen absorption/desorption properties of Li–Al–N–H composite

Li 3AlH 6 and LiNH 2 at a 1:3 molar ratio were mechanically milled to yield a Li–Al–N–H composite. The hydrogen storage properties of the composite were studied using thermogravimetry, differential scanning calorimetry, mass spectrometry, and X-ray diffraction. Addition of LiNH 2 lowered the decomposition temperature of Li 3AlH 6. The Li–Al–N–H composite began to release hydrogen at around 110 °C, which was 90 °C lower than the initial desorption temperature of Li 3AlH 6. About 7.46 wt% of hydrogen was released from the composite after heating from room temperature to 500 °C. A total hydrogen desorption capacity of 8.15 wt% was obtained after accounting for hydrogen released in the ball-milling process. The resulting dehydrogenated composite absorbed 3.56 wt% of hydrogen at 400 °C under a hydrogen pressure of 110 bar. The hydrogen absorption capacity and kinetic properties of the Li–Al–N–H composite significantly improved when CeF 3 was added to the composite. A maximum hydrogen absorption capacity of 4.8 wt% was reached when the composite was doped with 2 mol% CeF 3.

The interaction of CO and Li at a Ru( [formula omitted]) surface—a thermal desorption study

The interaction of carbon monoxide with the alkali metal lithium is studied on the single crystal substrate ruthenium surface Ru(0 0 1). The exceptionally strong interaction between CO and Li is investigated under various CO and Li coverages. Temperature programmed desorption spectroscopy shows the shift of the low coverage CO desorption peak ( θ CO<0.05) from its initial desorption temperature at 520–840 K when the lithium coverage is increased from zero to 1/3 of a mono-layer. Above that, the CO desorption temperature does no longer shift, but the desorption is concentrated in a single sharp Li/CO codesorption feature. Even stronger interaction of CO and Li is seen on a gold covered Ru surface (Au/Ru(0 0 1)). Au blocks the adsorption of CO. In the presence of Li however CO adsorbs readily. The uptake is roughly half that of the bare Ru surface and the thermal desorption occurs only above 900 K with the strong codesorption feature of Li and CO at 1080 K. The formation of a Au/Li alloy on the Ru substrate is confirmed.

Comportement transitoire d'une machine frigorifique à adsorption. Étude expérimentale du système alcool/charbon actif

The objective of this article is to present an experimental study of an adsorption refrigerator, accounting for the transient phenomena in each component of the machine, in particular in the adsorber. The couples adsorbate/adsorbent investigated (activated carbon/methanol or ethanol) have been chosen on the basis of an earlier comparative study. We have performed a full series of experiments to investigate the transient evolution of temperatures, pressures and the cycled mass, in a discontinuous cycle, and along the components of the refrigerating machine. The influence of various parameters is studied by varying one at a time: adsorbate/adsorbent couple, alcohol load in adsorber, alcohol flowrate, heating power, initial desorption temperature. All these experimental observations are discussed and compared to transient models developed in a separate article.