NaAlH4 Research Articles

Sodium alanate in-situ doped with Ti2C MXene with enhanced hydrogen storage properties

NaAlH4 is a reversible hydrogen storage material and has attracted great attention recently. However, the application of NaAlH4 in hydrogen storage still has great difficulties. In this study, 2D MXene Ti2C-doped NaAlH4 samples were prepared in-situ by reaction ball milling of NaH under moderate condition. TPD measurement results show that all the as-prepared samples exhibit good thermodynamic performance except for the sample doped with 1 wt% Ti2C. And DSC analysis results show that at the heating rate of 5 K/min, the first and second dehydrogenation peak temperatures of the sample doped with 7 wt% Ti2C were 127.1 °C and 150.6 °C respectively, which are 57.4 °C and 123.6 °C lower than those of pure NaAlH4 (after ball milling), respectively. Meanwhile, NaH/Al-7 wt.% Ti2C sample displays a superior kinetics behavior. Isothermal hydrogen evolution curves show that NaH/Al-7 wt.%Ti2C released 5.21 wt% H2 within 30 min at 150 °C and then absorbs 5.2 wt% H2 in 90 s at 120 °C. Even at a lower temperature of 80 °C, the sample still absorbed 4.71 wt% H2 within 60 min. In addition, almost no release capacity attenuation was observed for NaH/Al-7 wt.%Ti2C after 10 hydrogen absorption/desorption cycles. The improvement of the hydrogen storage properties can be ascribed to the high reactivity of NaAlH4 produced in situ and catalysis of lamellar Ti3+/0 species formed by the reduction of high valent Ti in Ti2C during ball milling.

HYDROGEN SORPTION IMPROVEMENT OF NaAlH4 CATALYSED BY K2 SiF6 FOR SOLID STATE HYDROGEN STORAGE

Sodium alanate (NaAlH4) has been recognised as a complex metal hydride that is frequently used as a hydrogen storage material. However, dealing with its poor kinetic characteristics and high decomposition temperatures becomes challenging. This research added potassium hexafluorosilicate (K2SiF6) as a catalyst to reduce the dehydrogenation temperature and improve sorption kinetics compared to the undoped NaAlH4. The dehydrogenation temperature of the NaAlH4 composite with 10 wt.% K2SiF6 addition was determined to be 145°C, a decrease of about 31% compared to 210°C for the undoped NaAlH4. The 10 wt.% K2SiF6-added NaAlH4 samples released roughly 1.77 wt.% hydrogen at 200°C after 60 minutes of dehydrogenation, representing faster dehydrogenation kinetics, but the milled NaAlH4 only produced around 1.39 wt.% of hydrogen. According to Kissinger’s analysis, the apparent activation energy, Ea for the decomposition of NaAlH4 was 87.74 kJ/mol in 1st stage and for NaAlH4 10 wt.% K2SiF6 composite, lowered by 30.45 kJ/mol or 25.8% than as-milled NaAlH4 (118.19 kJ/mol). The enhancement of the dehydrogenation performance of the NaAlH4-K2SiF6 composite can be attributed to the formation of the new phases of KAlF4. These findings might alter the reaction pathway of the composite system and improve its thermodynamic properties. The improvement of dehydrogenation performance and the discovery of the role played by KAlF4 in the dehydrogenation process of the NaAlH4-K2SiF6 composite give us valuable insights for developing and optimising future hydrogen storage materials.

Catalytical Synthesis and In Situ Doping of Sodium Aluminum Hydride from Elements

Catalytical Synthesis and In Situ Doping of Sodium Aluminum Hydride from Elements

Application of green energy and environment-friendly decorative composite materials by using kinetic model with Sodium Alanate Nano carbon particle for building technologies

Hydrogen energy is the main key point to make the long-term energy be secure. The unit of an economic system is completed by hydrogen generation, storage, transit, and use. Nonetheless, its storage strategies have clashed with applications that need hydrogen on board. The zero-energy idea was designed to assist in the development of energy policies with the goal of developing and constructing sustainable communities and structures. The higher the scale, the more plausible a zero-energy hydrogen economy is. H2 and fuel cell storage work together optimally to reduce uncertainty. The potential systems based on Sodium Alanate (SA) under the kinetic model was motivated by the extensive use and intriguing features of diverse silicon carbon nanomaterials. The electrical characteristics, structural stability, and adsorption energies of hydrogen molecules are investigated. Sodium Alanate is used in hydrogen gas release to investigate its feasibility. Hydrogen sorption procedure inside a storage container is modeled based on hydrogen transport equations, generated heat transfers and kinetic formulas. In this research, a numerical solution is created and verified using previously acquired empirical findings. This study defines and optimizes the gravimetric H2 storage potential on the basis of SA using numerical simulation data.

NEW PIDHID UP TO THE MOVEMENT OF FIRE SAFETY WATER SYSTEMS

When obtaining estimates that characterize the level of fire safety of the hydrogen storage and supply system, there is an error due to the subjective nature of its occurrence. It is noted that it is possible to weaken the influence of the subjective nature on these estimates by using the probabilistic characteristics of failure of the main elements of the hydrogen storage and supply system. Such basic elements include a gas generator. It is shown that the diffusion processes between the hydroreactive sample and the liquid - water are accompanied by the appearance of gas bubbles located on the reacting surface. This process - chemical boiling is characterized by internal characteristics. Internal characteristics were obtained experimentally for hydroreactive samples based on sodium aluminum hydride, which are approximated by polynomials of the fourth order and represent the dependence of the diameter of gas bubbles and the generation frequency on the diameter of the reacting surface. It is noted that the characteristics of the gas generator depend on the orientation of the reacting surfaces of the hydroreactive sample. The growth rate of basic bubbles practically does not depend on the diameter of the reacting surface, and the size of this surface for the vertical arrangement of the reacting surface is several percent larger than for its horizontal arrangement. The most unfavorable mode of gas generation is the case when the reactive surface of the hydro-reactive sample is oriented downwards. It is shown that increasing the reliability of the gas generator of the hydrogen storage and supply system is possible due to the implementation of a hydroreactive sample with a polylike one - a passive method and due to the formation of hydrodynamic forces acting on gas bubbles - an active method. These recommendations are embodied on the example of a hydrogen storage and supply system with vibrational movement of a hydroreactive sample, which is made in the form of a set of identical long cylinders assembled in a mesh cassette. Keywords: water saving and supply system, gas generator, fire safety, reliability.

Synthesis of Zn2TiO4 via solid-state method as a promising additive for dehydrogenation properties of NaAlH4

Sodium alanate (NaAlH4) has a high capacity for hydrogen, making it one of the most promising materials for storing hydrogen, but its slow dehydrogenation kinetics make it less practical. In this study, to speed up NaAlH4's dehydrogenation rate and improve its dehydrogenation properties, Zn2TiO4 synthesised through the method of solid-state was milled with NaAlH4. Zn2TiO4 additive remarkably reduces the initial temperature for the NaAlH4 to release hydrogen and fastens the dehydrogenation rate of NaAlH4. After adding different weight percentages of Zn2TiO4, the initial temperature for the NaAlH4 to release hydrogen was reduced to approximately 150 °C-165 °C (first dehydrogenation stage) and 190 °C-224 °C (second dehydrogenation stage), which is lower by 40 °C-55 °C than as-milled NaAlH4. The NaAlH4–Zn2TiO4 system also fastened the dehydrogenation rate by 10–15 times more than as-milled NaAlH4. The dehydrogenation activation energies of the NaAlH4 were also downshifted to 86.2 kJ/mol (first dehydrogenation stage) and 92.4 kJ/mol (second dehydrogenation stage) with the addition of Zn2TiO4. The activation energies were reduced by 26% (first dehydrogenation stage) and 24% (second dehydrogenation stage) illustrating the superior effect of Zn2TiO4. X-ray diffraction analysis discovered that TiZn2 and AlTi3 formed during the heating process are responsible for the enhanced performance of NaAlH4.

Performance analysis of sodium alanate hydride reactor with different nanofluids

The thermal management of the hydride based hydrogen storage reactor is the key factor to realize the complete storing potential of hydrides. In this regards a hydride reactor filled with sodium alanate in multiple tubes is numerically analyzed for absorption process. Based on various governing equations, a mathematical model of hydride reactor is developed and validated with the help of ANSYS Fluent. The hydride reactor uses mainly water or oil for heat exchange during hydrogen sorption. In the present study conventional heat transfer fluid (HTF) is replaced with the nanofluid since it has a greater heat exchange properties. The CuO/HTF, Al2O3/HTF and MgO/HTF nanofluids are selected based on previous studies and results of numerical experiment are recorded. The outcomes are attained for various parameters such as material and concentration of nanoparticles, supply pressure of hydrogen and inlet temperature of heat exchange fluid. The CuO/HTF nanofluid with concentration of 5 vol% exhibited better rate of absorption in comparison with other vol% concentrations and other selected nanofluids. It shows improvement in hydrogen absorption time up to 14% under selected conditions. Additionally, it is observed that CuO/HTF nanofluid with 5 vol% concentration is thermodynamically superior to other selected nanofluids; as a result it enhances the rate of the heat exchange up to 10% for hydride reactor. It is realized that the performance of CuO/HTF nanofluid with 5 vol% concentration is superior among picked nanofluids. Therefore for the hydride reactor the use the nanofluid is advantageous.

Electronic structure and stability of a pure sodium alanate clusters Na12Al12H48, and the interstitial space-doped with Ti, C and H atoms, as a promising hydrogen storage system: Density functional theory

Sodium alanate is a complex aluminium hydrogen, which has recently attracted more attention because it can be used as an effective hydrogen storage material. Our goal is to investigate the electronic structure and stability characteristics of promising hydrogen storage materials, including sodium alanate, Na12Al12H48 (12 units of NaAlH4), and which doped (interstitial defects) with Ti, C, and H atoms. The B3lyp/Sto-3G density functional theory based on quantum mechanical calculations uses DFT to obtain crucial information on chemical stability and reactions, such as possible structures (optimal bond length), electronegativity (ω), hardness (η), softness (S), ionization potential (IP), electron affinity (EA), energy gap (Eg), electronic chemical potential (μ), Fermi energy level (EF), maximum charge transfer (ΔN max), work function (ɸ), and electrophilicity (χ). These DFT-based global reactivity descriptors are sufficient to provide a better understanding of chemical systems in terms of their stability and reactivity. The interstitial doping by these atom positions places all binding lengths without any other significant change from the Na12Al12H48 crystal structure. Na12Al12H48 sodium lanate is slightly distorted. Na12Al12H48–H is very reactive and stability is low. The Na12Al12H48 –H cluster is expected to be promising in the formation of new compounds. On the other hand, the higher band gap values found for pure Na12Al12H48 clusters correspond to greater stability. Analysis of the length of the bonds and electronic properties shows that the sodium alanate grid was relatively uninfluenced by the interstitial space enriched with Ti, C, and H atoms. These results also show that the role of the C, Ti, and H atoms added to sodium alanates is not a “interstitial space doping” element but a catalyst.

Hydrogen-assisted one-pot synthesis of ultrasmall TiC nanoparticles enhancing hydrogen cycling of sodium alanate

Sodium alanate, NaAlH4, has great potential as a hydrogen carrier but suffers from sluggish kinetics and poor reversibility caused by high energy barriers. Transition metal-based catalysts are especially effective in reducing kinetic energy barriers for hydrogen cycling of NaAlH4. Herein, we demonstrate a facile fabrication of TiC nanoparticles with 2–4 nm in size supported on carbon (nano-TiC@C). The resultant product consists of approximately 49.2 wt% of TiC and 50.8 wt% of C, and exhibits high and stable catalytic activity for hydrogen storage process of NaAlH4. The 7 wt% nano-TiC@C-containing NaAlH4 releases 5 wt% H2 starting from 65 °C and reabsorbs all released hydrogen at 30 °C under 100 bar H2, outperforming NaAlH4 modified by commercial TiC nanoparticles (∼50 nm in size). The enhancement is related to the ultrasmall size and high reactive activity of as-synthesized TiC nanoparticles. Moreover, the weak electronegativity of C prevents the formation of Na-based by-products, which are often observed in oxide and halide-containing systems. This finding sheds light on how to design and synthesize high-performance catalytic additives for light-metal hydride-based hydrogen storage materials.

Dehydrogenation and low-pressure hydrogenation properties of NaAlH4 confined in mesoporous carbon black for hydrogen storage

For hydrogen to be successfully used as an energy carrier in a new renewable energy driven economy, more efficient hydrogen storage technologies have to be found. Solid-state hydrogen storage in complex metal hydrides, such as sodium alanate (NaAlH4), is a well-researched candidate for this application. A series of NaAlH4/mesoporous carbon black composites, with high NaAlH4 content (50–90 wt%), prepared via ball milling have demonstrated significantly lower dehydrogenation temperatures with intense dehydrogenation starting at ∼373 K compared to bulk alanate's ≥ 456 K. Dehydrogenation/hydrogenation cycling experiments have demonstrated partial hydrogenation at 6 MPa H2 and 423 K. The cycling experiments combined with temperature-programmed dehydrogenation and powder X-ray diffraction have given insight into the fundamental processes driving the H2 release and uptake in the NaAlH4/carbon composites. It is established that most of the hydrogenation behavior can be attributed to the Na3AlH6 ↔ NaH transition.

Constructal design of weight optimized metal hydride storage device embedded with ribbed honeycomb

Solid state storage of hydrogen offers few advantages over compressed and liquefied forms. As heat transfer being the major factor controlling charging and discharging, several thermal enhancement methods were reported in literature. However parasitic weight of thermal enhancement structures embedded to the storage bed can reduce its gravimetric storage capacity. As total weight of the device for given hydrogenation capacity and charging rate being an important factor, these structures needs to be weight optimized. The present study propose a ribbed honeycomb embedded to the multi-tubular storage device with sodium alanate as the storage alloy. The shape and size of this conform to the constructal law, analogous to bio transport systems. This ensures efficient transfer of sorption heat from the point of maximum temperature in the hydride bed to the coolant. The device designed for charging 0.01 kg of hydrogen in 10 min weighs 1.2 kg at optimum length/thickness ratio. This numerical study is conducted using COMSOL Multiphysics™ commercial code.

Tribochemically driven dehydrogenation of undoped sodium alanate under room temperature.

An application of mechanical energy was explored as a new non-thermal method to drive H2 emission from undoped sodium alanate at room temperature. It was found that mild rubbing of NaAlH4 pellets under vacuum led to intensive and almost instantaneous gas emission. The dominating species in the emitted gases was H2 (>99%). Traces of mono- and polyalanes, NaAlH4 vapours, CO2 and other non-identified gases were registered. H2 emission involved several first-order processes, whose characteristic time constants ranged widely from 0.6 to 465 s. None of the dehydrogenation reactions could be connected to either the thermal effect of friction or the direct coupling of mechanical forces to the energy landscape of chemical reactions. In turn, it was suggested that the tribochemical reactions can be triggered by plastic deformation and shearing. A linked diffusion-wear model of NaAlH4 triboinduced dehydrogenation, which consistently explains all empirical findings, was put forward.

Effects of surface morphology changes on FTIR-ATR spectroscopy with compacted Sodium Alanate (NaAlH4) during cycling

The hydrogen content during ab-/desorption of complex metal hydrides can be monitored via FTIR-ATR spectroscopy. Through cycling, the surface morphology of the pellet sample may alter due to the various material changes (e.g., granularity, volume, composition) and contribute to the spectral changes in an undesirable way.Therefore, the desorption of the first reaction step of TiCl3-doped NaAlH4 compacts was investigated in terms of optical signal stability. It was found that optical signal degradation occurs with an increasing number of ab-/desorption cycles. Different hydrogen cycling procedures identified changes in temperature during cycling to further degrade the signal. Using SEM and SFM measurements, a roughening of the pellet surface was observed as an effect of cycling. For reliable optical monitoring, different approaches to ensure long-term signal-coupling have been applied and their benefits compared. Thereby, dimensional changes in the surface flatness were found to be the dominant factor controlling the optical signal quality.The experimental results allow a more adequate operation of the measurement method and may be relevant for similar optical sensing applications, especially for “fuel level sensors” needed for various solid-state hydrogen storage systems.

CoFe2O4 synthesized via a solvothermal method for improved dehydrogenation of NaAlH4

The effect of cobalt ferrite (CoFe2O4) nanopowder synthesised through a solvothermal method on the dehydrogenation properties of sodium alanate (NaAlH4) was studied for the first time. The onset decomposition temperature of NaAlH4 is significantly reduced after milling with CoFe2O4, in which the 10 wt% CoFe2O4-doped NaAlH4 sample starts to decompose at ∼100 °C. In contrast, the as-milled NaAlH4 begins to decompose at ∼200 °C, ∼100 °C higher than the doped sample. With respect to desorption kinetic at constant temperature of 150 °C, the 10 wt% CoFe2O4-doped NaAlH4 sample desorbed ∼2.2 wt% hydrogen within 30 min, whereas the as-milled NaAlH4 only desorbed below 0.2 wt% hydrogen. The Kissinger plot exhibited that the apparent activation energy (EA) for hydrogen release from NaAlH4 is significantly reduced after adding with 10 wt% CoFe2O4-doped NaAlH4. The EA values for the first and second stage dehydrogenation of the 10 wt% CoFe2O4-doped NaAlH4 composite are calculated as 80.3 and 88.2 kJ/mol, respectively, and these values are reduced at approximately 34.3 and 30.5 kJ/mol compared with the as-milled NaAlH4 (114.6 and 118.7 kJ/mol, respectively). Based on the X-ray diffraction result, the enhancement of desorption properties of NaAlH4 with the presence of CoFe2O4 is presumably due to the synergistic catalytic effect played by new active species (Co3O4 and Fe) that in situ formed during the desorption process.

Thermodynamic modeling of the sodium alanates and the Na–Al–H system

Abstract The thermodynamic properties of the Al –Na and Na–Al – H systems have been assessed by combining the “calculation of phase diagram” approach with first-principles predictions. The Gibbs energies of the individual phases were thermodynamically modeled, where the model parameters were obtained from best fit optimizations to combined experimental and first-principles predicted finite temperature data. The first-principles thermodynamic predictions were based upon density functional theory ground state minimizations and direct method lattice dynamics. The predictions proved to be important adjuncts to the assessments whenever experimental measurements were lacking or not feasible. It was shown that the phase stability conditions of sodium alanates, NaAlH4 and Na3AlH6, were well described with the present models.

Modeling and simulation of hydrogenation process of NaAlH4

Metal hydride systems offer a technological avenue for high-energy hydrogen-density storage devices for a range of transit and mobile applications. Because of its high-coupling thermal transfer, mass transfer, and chemical kinetics, metal hydride systems offer many possibilities. The purpose of this paper is to model and simulate quick refuelling of a 9 kg storage tank filled with sodium alanate. The hydride bed within the canister had a material density of 0.62 g ml of NaAlH4. Before each run, the canister is pressurized and heated. A simulation technique is designed and validated by what has been done to achieve and noted as the optimum design for the storage canister in literature. The use of the simulation tool for various storage concepts and geometries results in the final design. In this end, we have confirmed Ansys as an effective simulation tool to model hydrogen storage (absorption) to precisely forecast the replenishment of hydrogen and release processes for storage systems based on hydride of metals.

Hydrogen Desorption Mechanism of Sodium Alanate Doped with different Catalyst

Hydrogen Desorption Mechanism of Sodium Alanate Doped with different Catalyst

Influence of Nanoconfinement on the Hydrogen Release Processes from Sodium Alanate

Sodium alanate (NaAlH4) is a prospective H2 storage material for stationary and mobile applications, as NaAlH4 contains 7.4 wt% of H2, and it is possible to do multiple H2 release and accumulation cycles. Nanoconfinement is a potential solution to enhance the H2 release properties of NaAlH4. To optimize the supporting material and the synthesis method used for the nanoconfinement of NaAlH4, a better understanding of the influence of nanoconfinement on the H2 release processes is necessary. Thus, the H2 release from bulk, purely nanoconfined, and intermediate NaAlH4 is measured at different temperature ramp rates, and the characteristic parameters for each hydrogen release process are determined. Activation energies for each process are determined using the Kissinger method, and the effect of nanoconfinement on the activation energies is analysed. The impact of nanoconfinement on the H2 release processes from NaAlH4 and the limitations of each process in case of bulk and nanoconfined NaAlH4 are presented and discussed. Nanoconfinement of NaAlH4 decreases activation energies of the initial reversible H2 release steps to between 30 and 45 kJ mol−1 and increased the activation energy of the last irreversible H2 release step to over 210 kJ mol−1.

Titanium Hydride Nanoplates Enable 5 wt% of Reversible Hydrogen Storage by Sodium Alanate below 80°C.

Sodium alanate (NaAlH4) with 5.6 wt% of hydrogen capacity suffers seriously from the sluggish kinetics for reversible hydrogen storage. Ti-based dopants such as TiCl4, TiCl3, TiF3, and TiO2 are prominent in enhancing the dehydrogenation kinetics and hence reducing the operation temperature. The tradeoff, however, is a considerable decrease of the reversible hydrogen capacity, which largely lowers the practical value of NaAlH4. Here, we successfully synthesized a new Ti-dopant, i.e., TiH2 as nanoplates with ~50 nm in lateral size and ~15 nm in thickness by an ultrasound-driven metathesis reaction between TiCl4 and LiH in THF with graphene as supports (denoted as NP-TiH2@G). Doping of 7 wt% NP-TiH2@G enables a full dehydrogenation of NaAlH4 at 80°C and rehydrogenation at 30°C under 100 atm H2 with a reversible hydrogen capacity of 5 wt%, superior to all literature results reported so far. This indicates that nanostructured TiH2 is much more effective than Ti-dopants in improving the hydrogen storage performance of NaAlH4. Our finding not only pushes the practical application of NaAlH4 forward greatly but also opens up new opportunities to tailor the kinetics with the minimal capacity loss.

Cerium hydride generated during ball milling and enhanced by graphene for tailoring hydrogen sorption properties of sodium alanate

In this study, NaAlH4−based hydrogen storage materials with dopants were prepared by a two-steps in-situ ball milling method. The dopants adopted included Ce, few layer graphene (FLG), Ce + FLG, and CeH2.51. The hydrogen storage materials were studied by non-isothermal and isothermal hydrogen desorption measurements, X-ray diffractions analysis, cycling sorption tests, and morphology analysis. The hydrogen storage performance of the as-prepared NaAlH4 with Ce addition is much better than that with CeH2.51 addition. This is due to that the impact of Ce occurs from the body to the surface of the materials. The addition of FLG further enhances the impact of Ce on the hydrogen storage performance of the materials. The hydrogen storage capacity, hydrogen sorption kinetics, and cycle performance of NaAlH4 with Ce + FLG additions are all better than NaAlH4 materials with the addition of either Ce or FLG alone. The NaAlH4 with Ce and FLG addition starts to release hydrogen at 85 °C and achieves a capacity of 5.06 wt% after heated to 200 °C. The capacity maintains at 4.91 wt% (94.7% of the theoretical value) for up to 8 cycles. At 110 °C, the material can release isothermally a hydrogen capacity of 2.8 wt% within 2 h. The activation energies for the two hydrogen desorption steps of NaAlH4 with Ce and FLG addition are estimated to be 106.99 and 125.91 kJ mol−1 H2, respectively. The related mechanisms were studied with first-principle and experimental methods.