Hydrogen Storage Properties Of NaAlH4 Research Articles

Enhancement of hydrogen storage properties of NaAlH4 catalyzed by CuFe2O4

This study describes the hydrogen storage performance of NaAlH4 with the addition of CuFe2O4 additive. The results were compared with undoped NaAlH4. For the first and second steps of dehydrogenation, the CuFe2O4-doped NaAlH4 liberated hydrogen at 150 °C and 220 °C, whereas as-milled NaAlH4 released hydrogen at 190 °C and 290 °C, respectively. The desorption kinetic analysis unveiled that the doped system liberated around 1.5 and 4.4 wt% hydrogen within 120 min at 150 and 200 °C, respectively. Meanwhile, the undoped NaAlH4 only desorbed 0.5 and 3.6 wt% hydrogen, respectively, under identical conditions. The activation energy for the doped system at the first step of dehydrogenation was decreased from 114.7 to 92.5 kJ/mol, while reduced from 125.2 to 98.1 kJ/mol at the second stage. The synergistic impact between the in-situ formed Cu2O and Fe during the heating process indicated that these active species are superior in boosting the hydrogen storage performance of NaAlH4.

Tuning the hydrogen thermodynamics of NaAlH4 by encapsulation within a titanium shell

The use of NaAlH4 as a practical hydrogen storage material has seen extensive progress. However, it is still difficult to control the hydrogen storage properties of NaAlH4 and in particular its hydrogen thermodynamics. Herein, we demonstrate the potential of core-shell NaAlH4@Ti nanostructures in altering the hydrogen storage properties of NaAlH4. To this aim, a facile solvent evaporation method was developed to enable the making of freestanding NaAlH4 nanoparticles and their individual encapsulation within a Ti shell. These core-shell nanostructures enabled: (i) an effective confining environment for NaAlH4 and its dehydrogenation products, and (b) fast hydrogen kinetics due to a weakening of the Al–H bond and the shorter diffusion lengths. At 180 °C, a reversible hydrogen storage capacity of 4.4 mass% was observed. More remarkably, this core-shell approach enabled a shift in the equilibrium plateau pressure, therefore demonstrating the possibility to control the hydrogen thermodynamics of NaAlH4 at the nanoscale.

Effect of (Ti0.35V0.65)0.86Fe0.14Hy on synthesis and hydrogen storage properties of NaAlH4

The (Ti0.35V0.65)0.86Fe0.14Hy powder was prepared by melting, annealing and H2-assisted-crushed method to avoid passivation. Then [(Ti0.35V0.65)0.86Fe0.14Hy]x/100-NaAlH4 composite system were synthesized using a two-step in-situ-milling method with the proportion of n (NaH):n (Al):n (Graphene):n (alloy) = 100:100:5:x (x = 2,5,8). It was found that lattice distortion had occurred on the alloy after 190hindividually milling, and the hydrogen storage capacity had decreased significantly to 1.10 wt%. However, after long-term composite milling, the alloy could still reduce the hydrogen pressure required for the synthesis of NaAlH4, besides it could effectively reduce the hydriding/dehydriding temperature and improve the kinetic properties. This may due to the alloy's ability to dissociate H2 and transfer H at room temperature, thereby enhancing the opportunity for direct contact between the matrix and H. In this study, x = 5 was the optimal alloy addition ratio, its dehydrogenation capacity at the 1st cycle reached 5.04 wt%; and at the 2nd and subsequent cycles, it remained rather stable at 4.40 wt%.

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.

Synergistic Effect of CeF3 Nanoparticles Supported on Ti3C2 MXene for Catalyzing Hydrogen Storage of NaAlH4

The rational design of catalysts is extraordinarily significant for facilitating the dehydrogenation kinetics of NaAlH4. Herein, CeF3 nanoparticles supported on Ti3C2 MXene (CeF3/Ti3C2) were successfully synthesized and applied to catalyze the hydrogen storage properties of NaAlH4. With the addition of 10 wt % CeF3/Ti3C2, the onset dehydrogenation temperature was lowered to 87 °C and more than 3.0 wt % H2 can be released at 140 °C within 6 min. Moreover, the composite exhibited wonderful stability and reversibility with 94.5% capacity retention after 10 cycles of continued tests. The compositional and structural analysis demonstrated that a Ti–F–Ce structure at the interface between CeF3 and Ti3C2 was formed and remained stable during the ball milling, urging the stabilization of Ti0 catalytic species in the hydrogenation/dehydrogenation of NaAlH4. The remarkably enhanced hydrogen storage behavior was attributed to the synergy effects of Ti0 species and the outstanding stable structure of Ti–F–Ce from the CeF3/Ti3C2 catalyst. The findings have widened the road for the rational design of high efficiency catalysts to improve the hydrogen storage performance of NaAlH4.

Improved hydrogen storage properties of NaAlH4[sbnd]MgH2[sbnd]LiBH4 ternary-hydride system catalyzed by TiF3

In this study, the hydrogen storage properties and reaction mechanisms of a NaAlH4MgH2LiBH4 destabilized system with a TiF3 additive are investigated for the first time. It was found that the addition of TiF3 resulted in both decreased decomposition temperature and improved sorption kinetics compared with that of un-doped NaAlH4MgH2LiBH4. The onset dehydrogenation temperature for all stages in the TiF3-doped composite was reduced by 100 °C, 30 °C and 20 °C compared with the un-doped composite. For the rehydrogenation kinetics, the TiF3-added sample absorbed ∼4.5 wt.% hydrogen at 350 °C after 30 min of rehydrogenation; however, the un-doped composite only absorbed ∼3.5 wt.% hydrogen. Differential scanning calorimetry indicated that the number of thermal events in the NaAlH4MgH2LiBH4 composite reduced from six to four after doping with TiF3. It is believed that the formation of Ti- and F-containing species during ball milling or dehydrogenation may be responsible for the catalytic effects, further improving the hydrogen storage properties of the TiF3-doped NaAlH4MgH2LiBH4 composite system.

Remarkably improved hydrogen storage properties of NaAlH4 doped with 2D titanium carbide

Abstract A 2D Ti3C2 MXene is introduced into NaAlH4 to improve its hydrogen storage properties for the first time. In the presence of Ti3C2, the operating temperatures for hydrogen storage in NaAlH4 are remarkably reduced, and the hydrogenation/dehydrogenation kinetics are significantly enhanced. The onset dehydrogenation temperature of the 7 wt% Ti3C2-containing NaAlH4 sample is reduced to 100 °C, and hydrogen recharging starts at 50 °C. Approximately 4.7 wt% hydrogen is released from the NaAlH4-7 wt% Ti3C2 sample within 100 min at 140 °C, and the dehydrogenated sample absorbs 4.6 wt% hydrogen within 60 min at 120 °C. However, pristine NaAlH4 only absorbs 0.4 wt% hydrogen under identical conditions. Further cycling measurements show significantly improved cycling stability for the Ti3C2-containing NaAlH4; the hydrogenation/dehydrogenation behaviour remains nearly constant after 10 cycles. XRD and XPS analyses reveal that the Ti3C2 reacts with NaAlH4 and is reduced to metallic Ti and Ti3+ species, which are responsible for the lowered operating temperatures and improved dehydrogenation/hydrogenation kinetics.

Ultrafine Nanocrystalline CeO2@C-Containing NaAlH4 with Fast Kinetics and Good Reversibility for Hydrogen Storage.

A nanocrystalline CeO2@C-containing NaAlH4 composite is successfully synthesized in situ by hydrogenating a NaH-Al mixture doped with CeO2@C. Compared with NaAlH4 , the as-prepared CeO2@C-containing NaAlH4 composite, with a minor amount of excess Al, exhibits significantly improved hydrogen storage properties. The dehydrogenation onset temperature of the hydrogenated [NaH-Al-7 wt % CeO2@C]-0.04Al sample is 77 °C lower than that of the pristine sample because of a reduced kinetic barrier. More importantly, the dehydrogenated sample absorbs ∼4.7 wt % hydrogen within 35 min at 100°C and 10 MPa of hydrogen. Compositional and structural analyses reveal that CeO2 is converted to CeH2 during ball milling and that the newly formed CeH2 works with the excess of Al to synergistically improve the hydrogen storage properties of NaAlH4. Our findings will aid in the rational design of novel catalyst-doped complex hydride systems with low operating temperatures, fast kinetics, and long-term cyclability.

Hydrogen Storage Properties of Complex Metal Hydride-Carbon Materials

Hydrogen storage properties of NaAlH4 can be improved by mixing it with Co/carbon catalysts. The importance of cobalt nanoparticles was established by varying the amount of active cobalt in the reaction vessel. This was achieved either by keeping the weight of NaAlH4 and carbon constant while varying the amount of Co/carbon catalyst used or by poisoning the cobalt active site with CO. Another approach to improve the hydrogen storage properties of complex metal hydride is through nano-confinement of the hydride in carbon pores. LiBH4–carbon composite formed via liquid phase infusion of LiBH4 into carbon was examined for reversibility in the hydriding/dehydriding cycles. The physical constraints imposed by the carbon nano-pores appeared to be effective in deterring the loss of cyclability due to sintering of the hydride. The loss in hydrogen storage appeared to be the result of LiBH4 reaction with impurities/reactive functional groups on the carbon.

Size effect on hydrogen storage properties of NaAlH4 confined in uniform porous carbons

Uniform porous carbons with pore size of 200nm, 60nm, 30nm and 4nm were separately synthesized using hard-template method, and nanoparticles of NaAlH4 have been infiltrated into the above porous carbons. A correlation between pore size and hydrogen desorption kinetics of NaAlH4 is established. In contrast with bulk NaAlH4, all of the confined NaAlH4 exhibit a single-step dehydrogenation process to form NaH/Al product. However, the onset and peak hydrogen desorption temperatures are significantly influenced by the pore size of carbon. As the pore size is reduced to 30nm, NaAlH4 starts to decompose at temperature of about 100°C, with a dehydrogenation peak of 172°C. The apparent activation energy for dehydrogenation is estimated to be 84.9 and 69.7kJ/mol for the NaAlH4 confined in 30 and 4nm porous carbons, reduced by 43 and 58kJ/mol contrast to the first step of bulk NaAlH4, respectively. Besides, by confining NaAlH4 into porous carbon with pore size≤30nm, the in situ generated NaH can decompose at a temperature below 250°C, i.e. reduction of the temperature for 100°C compared with that generated by decomposition of bulk NaAlH4. Thus all of hydrogen in NaAlH4 can be released and utilized at a relatively moderate condition without doping additives. Cycling investigation shows that smaller size exerts a favorable effect on the hydrogen storage capacity retention.

Reversible hydrogen storage properties of NaAlH4 enhanced with TiN catalyst

Hydrogen storage properties of commercial NaAlH4 doped efficient TiN catalyst have been systematically investigated. The dehydrogenation and reversibility of the 2mol% TiN-doped NaAlH4 (2%TiN–NaAlH4) system have been studied. It is found that TiN catalyst improves the dehydrogenation kinetics and decreases the dehydrogenation temperature of NaAlH4. Interestingly, the onset dehydrogenation temperature of 2%TiN–NaAlH4 system gets lowered to about 130.0°C with a faster kinetics, and the dehydrogenation rate reaches a maximum value at 183.5°C. The apparent activation energy for the first and the second dehydrogenation step of TiN–NaAlH4 system is estimated to be 91.70kJmol−1 and 99.93kJmol−1, respectively. The dehydrogenation and hydrogenation behaviors of 2%TiN–NaAlH4 are investigated under different hydrogen pressures using high-pressure differential scanning calorimetry (HP-DSC). The 2%TiN–NaAlH4 system exhibits excellent reversibility at moderate conditions. Moreover, the dehydrogenation and hydrogenation processes of the 2%TiN–NaAlH4 system are also discussed.

Significantly improved hydrogen storage properties of NaAlH4 catalyzed by Ce-based nanoparticles

NaAlH4, a prototypical high energy density complex hydride, possesses a favorable thermodynamics and high hydrogen storage capacity. However, the poor kinetics and degradation of cycling stability retard its practical application. To ease these problems, CeB6, CeF3 and CeO2 nanoparticles with a size of about 10 nm are synthesized by the wet-chemistry method and introduced into NaAlH4 systems as additives in this work. The results show that all of the nanoparticles are effective in improving the hydriding–dehydriding kinetics of NaAlH4, and nano-CeB6 possesses the highest catalytic activity. The rehydrogenation of dehydrogenated NaAlH4 doped with nano-CeB6 can be accomplished in less than 20 min with a high capacity of 4.9 wt%, which shows a 20% increase in capacity compared to that of chloride-doped NaAlH4. Due to the structural stability and good dispersion of nano-CeB6 and nano-CeF3, a favorable cycling stability with high capacity retention is achieved for their doped samples. Moreover, hydrogen can be released from the hydrogenated sample doped with nano-CeB6 at a temperature as low as 75 °C, fulfilling the operation temperature of a PEM fuel cell. In the nano-CeO2 doped NaAlH4 system, CeO2 is first reduced to CeH2.51. In the subsequent cycles, the formed CeH2.51 gradually transforms into Ce–Al, and simultaneously the kinetics of the doped system is further enhanced. It is believed that the utilization of Ce-based nanoparticles as catalysts would substantially improve the practical applications of NaAlH4 for hydrogen storage.

Improvement of the hydrogen storage kinetics of NaAlH4 with nanocrystalline titanium dioxide loaded carbon spheres (Ti-CSs) by melt infiltration

Nanocrystalline titanium dioxide loaded carbon spheres (Ti-CSs) with 10wt% TiO2 were synthesized through an easy one-step method using phenolic resols, titania nanoparticles and Pluronic F127 as organic carbon sources, inorganic precursors and surfactant, respectively. The results show that the as-prepared Ti-CSs composite is spherical shape with a diameter ranging from 0.3 to 2 μm, and rutile TiO2 nanoparticles are distributed on the surface of the carbon spheres. Then the kinetics of NaAlH4 was improved through depositing it on the surface of as-prepared Ti-CSs by melt infiltration. The results show that NaAlH4 with Ti-CSs exhibits better hydrogen desorption kinetics than TiF3 or nanocrystalline TiO2 catalysted-NaAlH4, and it starts to release hydrogen at about 40 °C and releases about 25% of the hydrogen content during heating to 60 °C. The results from SEM and XPS show that hydrogen storage properties of NaAlH4 were considerably improved due to the formation of special structure during melt infiltration and the nanocrystalline TiO2 and/or amorphous phase Ti–Al clusters near the subsurface sites, which succeed in combining catalyst addition (TiO2 nanoparticles) and nanoconfinement to improve the kinetics of NaAlH4.

Improvement of the hydrogen storage kinetics of NaAlH4 with Ti-loaded high-ordered mesoporous carbons (Ti-OMCs) by melt infiltration

Combination of nanoconfinement and catalyst addition is a promising strategy to enhance the kinetics and reversibility of hydrogen storage in complex hydrides. Herein, Ti-loaded high-ordered mesoporous carbons (Ti-OMCs) were directly synthesized via a solvent evaporation induced self-assembly method (EISA) with in situ crystallization and carbonation technology using phenolic resols, tetrabutyl titanate (Ti(OBu)4) and triblock copolymer F127 as organic carbon sources, Ti sources and templates, respectively. The obtained Ti-OMCs exhibit uniform pore sizes (4 nm), high specific surface area (427.9 m2 g−1) and large pore volumes (0.34 cm3 g−1), which were used to combine catalyst addition and nanoconfinement to improve the hydrogen storage properties of NaAlH4 by melt infiltration. The hydrogen desorption curves show that NaAlH4 with Ti-OMCs exhibits better kinetic properties than both nanocrystalline TiO2 catalysed NaAlH4 and melt-infiltrated NaAlH4 with high ordered mesoporous carbons (OMCs). The hydrogen-release onset temperature of NaAlH4 with Ti-OMCs is reduced to less than 60 °C, and 80% hydrogen is released in less than 20 min. In addition, NaAlH4 with Ti-OMCs exhibit good reversibility and cycling stability, and the optimum rehydrogention temperature is 120 °C.

Effect of LaCl3 and Ti on Hydrogen Storage Properties of NaAlH4 and LiAlH4

Abstract The effects of additives Ti and LaCl3 on the hydrogen storage properties of NaAlH4 and LiAlH4 were investigated by the PCT (pressure-content-temperature) apparatus. NaAlH4 doped with LaCl3 and LiAlH4 doped with LaCl3 both show better capability of hydrogen release than the samples doped with Ti. The study on the first rehydrogenation cycle of NaAlH4 doped with 3 mol% LaCl3 finds that the dehydrogenation temperature has a marked decrease. In addition, the effect of LaCl3 content on hydrogen release of NaAlH4 is very obvious. The result indicates that the amount and rate of hydrogen release show the same change trends, increasing firstly and then decreasing with increasing of LaCl3 content. The sample doped with 3 mol% LaCl3 presents the best dehydrogenation properties in both the amount of hydrogen release and the desorption kinetics. The activation energy of the NaAlH4 sample doped with 3 mol% LaCl3 was measured to be 41.6 kJ/mol. This value is lower than that reported for the Ti-doped NaAlH4.

The effect of additives on the hydrogen storage properties of NaAlH4

The effect of Ti, Co, Ni and LaCl3 on hydrogen release of NaAlH4 was studied by pressure-content-temperature (PCT) equipment. The result showed that the sample doped with 3 mol% LaCl3 presented the largest amount of hydrogen release. Increasing the amount of LaCl3 from 1 to 6 mol% caused such marked changes in behavior that the amount and rate of hydrogen release increased first and then decreased. In addition, the study on the rehydrogenation temperature of NaAlH4 doped with 3 mol% LaCl3 showed that the doped sample during the first rehydrogenation cycle carried out in PCT at 110 °C under 8 MPa after being discharged of hydrogen at 270 °C presented the largest amount of hydrogen release.