Improved Hydrogen Storage Research Articles

Improved dehydrogenation kinetics of MgH2 due to NiMnAl

Mg based nanocomposites containing different concentrations of NiMnAl alloy is studied in present work. Doped alloy was prepared by arc melting and ball milled to get its nano structure. Structural and hydrogen desorption properties of the composites were examined by x-ray diffraction(XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy and energy dispersive x-ray analysis (EDX). TGA study showed higher desorption temperature for as-milled MgH2 compared to MgH2 −x wt% NiMnAl. Activation energy for hydrogen desorption was found to be −177.90, −173.09, −117.62 and −58.62 kJ mol−1 for as-milled MgH2 and MgH2 −x wt.% NiMnAl (x = 10, 25, 50) composites. In case of 50 wt% alloy additives the reduction of activation energy is 119.24 kJ mol−1 resulting in improved hydrogen storage. XRD studies for phase and purity of as-milled MgH2 revealed that maximum stable and improved phase alteration for Hydrogen sorption was obtained for 25 wt% alloy. Morphology by SEM were undertaken to investigate the effect of hydrogenation of nanostructured alloy. DSC studies shows that increasing the concentration of NiMnAl in MgH2 from 25 to 50 wt% the onset temperature of hydrogen absorption decreased to about 40 °C.

Severe Plastic Deformation and Additive Distribution in Mg-Fe to Improve Hydrogen Storage Properties

Severe Plastic Deformation and Additive Distribution in Mg-Fe to Improve Hydrogen Storage Properties

Superior catalytic activity of in situ reduced metallic Co for hydrogen storage in a Co(OH)2-containing LiBH4/2LiNH2 composite

Cobalt hydroxide (Co(OH)2) is introduced into the LiBH4/2LiNH2 composite to improve its hydrogen storage properties. The 0.05Co(OH)2-containing sample exhibits a significantly reduced dehydrogenation temperature and improved hydrogen storage reversibility. Its dehydrogenation onset temperature is as low as 70°C, representing the lowest onset dehydrogenation temperature for the known catalyst-added LiBH4/2LiNH2 system. At 200°C, approximately 9.1wt% of hydrogen is rapidly released from the 0.05Co(OH)2-containing sample within 15min, greatly superior to the pristine sample because nearly no hydrogen release from it is observed under identical conditions. More importantly, the dehydrogenated sample absorbs 1.1wt% of hydrogen at 350°C, achieving partial reversibility for hydrogen storage in the LiBNH system. Structural investigations reveal that the added Co(OH)2 is first reduced to metallic Co during ball milling, and the Co thus formed in situ serves as the active catalyst in improving the hydrogen storage properties of the LiBH4/2LiNH2 sample.

Improved hydrogen storage properties of MgH2 with Ni-based compounds

The nanoscaled Ni-based compounds (Ni3C, Ni3N, NiO and Ni2P) are synthesized by chemical methods. The MgH2-X (X = Ni3C, Ni3N, NiO and Ni2P) composites are prepared by mechanical ball-milling. The dehydrogenation properties of Mg-based composites are systematically studied using isothermal dehydrogenation apparatus, temperature-programmed desorption system and differential scanning calorimetry. It is experimentally confirmed that the dehydrogenation performance of the Mg-based materials ranks as following: MgH2Ni3C, MgH2Ni3N, MgH2NiO and MgH2Ni2P. The onset dehydrogenation temperatures of MgH2Ni3C, MgH2Ni3N, MgH2NiO and MgH2Ni2P are 160 °C, 180 °C, 205 °C and 248 °C, respectively. The four Mg-based composites respectively release 6.2, 4.9, 4.1 and 3.5 wt% H2 within 20 min at 300 °C. The activation energies of MgH2Ni3C, MgH2Ni3N, MgH2NiO and MgH2Ni2P are 97.8, 100.0, 119.7 and 132.5 kJ mol−1, respectively. It' found that the MgH2Ni3C composites exhibit the best hydrogen storage properties. Moreover, the catalytic mechanism of the Ni-based compounds is also discussed. It is found that Ni binding with low electron-negativity element is favorable for the dehydrogenation of the Mg-based composites.

Improved hydrogen storage properties of Mg-Li-Al-H composite system by milling with Fe2O3 powder

A sample of Fe2O3-doped 4MgH2-Li3AlH6 composite was prepared by the ball milling technique, and the hydrogen storage properties were investigated for the first time. Results showed that the addition of Fe2O3 powder reduced the decomposition temperature and improved de/hydrogenation kinetics compared with undoped 4MgH2-Li3AlH6. The onset decomposition temperature for the Fe2O3-doped 4MgH2-Li3AlH6 composite decreased by 75°C compared with that of the undoped composite. For the sorption kinetics, a hydrogen absorption capacity of 2.4wt% was reached after 60min in the 10wt% Fe2O3-doped 4MgH2-Li3AlH6 composite, whereas the neat composite absorbed 2.3wt% hydrogen under the same conditions. For desorption kinetics, the Fe2O3-doped 4MgH2-Li3AlH6 sample released 2.5wt% hydrogen under 10min of dehydrogenation, but the neat 4MgH2-Li3AlH6 composite only desorbed 2.0wt% hydrogen within the same period. The apparent activation energy calculated by Kissinger analysis for hydrogen desorption decreased to 112.9kJ/mol after Fe2O3 was added compared with the undoped composite, which was 145.4kJ/mol. The X-ray diffraction analysis shows the formation new phase of Li2Fe3O4 in the doped sample after ball milling processes that could act as the real catalyst in the Fe2O3-doped 4MgH2-Li3AlH6 composite.

Effects of Cu and Y substitution on hydrogen storage performance of TiFe0.86Mn0.1Y0.1−xCux

The aim of this study is to investigate systematically the remarkably improved hydrogen storage capacity and faster activation performance of TiFe0.86Mn0.1Y0.1−xCux where x = 0.01, 0.03, 0.05, 0.07, 0.09 alloys. The designed alloys were synthesized via water-cooled copper crucible and the phase analysis, morphology study and elemental analysis of as-synthesized alloys were investigated. Afterwards, the hydrogen storage performance and kinetic test of alloys powder were employed. The results show that the hydrogen storage capacity increases first and then decreases slightly with increase of Y additives, whereas the absorption/desorption plateau pressure and slop decreases, and the highest hydrogen capacity of TiFe0.86Mn0.1Y0.05Cu0.05 is achieved 1.89 wt% at 10 °C. The element Cu causes deterioration in hydrogen capacity but improves activation, and the capacity decreases with increase of Cu content. Furthermore, the activation and kinetics rate of each alloy is improved with secondary phase particles (CuY and Cu4Y) observed in scanning electron microscope/energy dispersive spectroscopy (SEM/EDS), and the TiFe0.86Mn0.1Y0.05Cu0.05 alloy shows fastest kinetic rate at 10 °C, this may ascribe to the secondary phase which provides new channels for hydrogen flux to penetrate into the matrix. The interfaces between the matrix and secondary phase particles are very active for hydrogen absorption and improve hydrogen absorption performance remarkably.

Enhanced hydrogen storage performances of LiBH4 modified with three-dimensional porous fluorinated graphene

Novel fluorinated graphene (FG) nano-sheets with three-dimensional (3D) porous structure were synthesized by one-pot hydrothermal reaction, and then ball milled with LiBH4 to prepare the hydrogen storage composite material. The LiBH4 with 20 wt.% FG composite begins to release hydrogen at 204 °C, 120 °C lower than that of pure LiBH4. Moreover, it can release 3.45 wt.% hydrogen at 400 °C within 1000 s, which is 2.57 times faster than pure LiBH4. The reversibility of the LiBH4–FG composite also has been enhanced, its absorption capacity still reaches 78.6% of initial hydrogen uptake at the 4th cycle. According to the phase composition analyses, F– can partially substitute the anionic H in LiBH4 or LiH, resulting in a favorable thermodynamic modification. Additionally, the activation energy (Ea) of hydrogen desorption of LiBH4 is reduced from 181.80 kJ/mol to 130.87 kJ/mol. The remarkably improved hydrogen storage performances of LiBH4 are largely attributed to the combined effects of the nano-modifying and the function of F anion of the FG.

Enhanced hydrogen storage in sandwich-structured rGO/Co1−xS/rGO hybrid papers through hydrogen spillover

Abstract Reduced graphene oxide (rGO) based two-dimensional (2D) structures have been fabricated for electrochemical hydrogen storage. However, the effective transfer of atomic hydrogen to adjacent rGO surfaces is suppressed by binders, which are widely used in conventional electrochemical hydrogen storage electrodes, leading to a confining of the performance of rGO for hydrogen storage. As a proof of concept experiment, a novel strategy is developed to fabricate the binder-free sandwich-structured rGO/Co1−xS/rGO hybrid paper via facile ball milling and filtration process. Based on the structure investigation, Co1−xS is immobilized in the space between the individual rGO sheets by the creation of chemical “bridges” (C S bonds). Through the C S bonds, the atomic hydrogen is transferred from Co1−xS to rGO accompanying a C H chemical bond formation. When used as an electrode, the hybrid paper exhibits an improved hydrogen storage capacity of 3.82 wt% and, most importantly, significant cycling stability for up to 50 cycles. Excluding the direct hydrogen storage contribution from the Co1−xS in the hybrid paper, the hydrogen storage ability of rGO is enhanced by 10× through the spillover effects caused by the Co1−xS modifier.

Improved hydrogen storage kinetics of nanocrystalline and amorphous Pr-Mg-Ni-based PrMg12-type alloys synthesized by mechanical milling

In this paper, the nanocrystalline and amorphous PrMg11Ni + x wt.% Ni (x = 100, 200) alloys were synthesized by mechanical milling. The gaseous and electrochemical hydrogen storage performances were studied in detail. The results reveal that increasing Ni content facilitates the glass forming of the alloys, and it significantly improves the gaseous and electrochemical hydrogen storage kinetics performance. Furthermore, milling time varying significantly affects the hydrogen storage properties of the alloys. The hydrogen capacity of the alloys first increases and then decreases with milling time prolonged. The hydriding rate and high-rate discharge ability (HRD) of the as-milled alloys have maximum values with milling time varying. But dehydriding rate always increases with milling time prolonged. The improved gaseous hydrogen storage kinetics of alloys are convinced to be ascribed to a reduction in hydrogen desorption activation energy caused by increasing Ni content and prolonging milling time.

Hydrogen adsorption of nickel-silica materials: Role of the SBA-15 porosity

In this work, SBA-15 support was impregnated with nickel in order to study the influence of different factors (metal content, support, method of preparation) on their hydrogen storage capacity. H2 adsorption was measured at low and high pressures (up to 10 and 40 bar) at 77 and 293 K, evaluating the influence of metallic nickel on such adsorption capacity. The properties of the prepared materials were studied by N2 adsorption-desorption, XRD, TPR, UV–Vis, TEM, SEM and XPS techniques. The results indicated the importance of the nickel dispersion on the support to improve hydrogen storage. Thus, Ni/SBA-15 (2.5) sample, in contrast to Ni/SBA-15 (2.5)-R, shows the higher hydrogen adsorption capacity at both 77 K and 293 K.

Optimal Surface Doping of Lead for Increased Electrochemical Insertion of Hydrogen into Palladium

Increasing the amount of hydrogen that is electrochemically inserted into materials is important for studying superconductivity and hydrogen embrittlement, and improving hydrogen storage capabilities. Surfaces can be engineered to accomplish this task with better insight into how the composition of a material's first few atomic layers affects the electrochemical insertion of hydrogen. To this end, different amounts of Pb were added to the 0.1M LiOH electrolyte to be deposited onto Pd cathodes during galvanostatic experiments. The investigated amount of added Pb was between 1μgcm−2 and 23μgcm−2 with respect to the geometric area of the Pd cathode. The optimum surface doping level 2.9μgcm−2 of Pb (∼1.4 mass equivalent monolayers) was found to achieve the highest quantity of inserted hydrogen at approximately −0.5V vs RHE. Additionally, the hydrogen content increased from PdH0.75 to PdH0.86 with increasing Pb amounts up to 2.9μgcm−2 at a constant current of −14.5mAcm−2. For comparison, the same change in hydrogen content from pressurized gas loading experiments would require an increase in hydrogen fugacity from about 6 to 1420 atm. Preliminary analysis concerning the adsorbed hydrogen chemical potential suggests the Pb is affecting the balance between the Volmer, Heyrovsky, and Tafel reaction rates, which changes the hydrogen surface chemical potential, and ultimately controls the hydrogen insertion. Furthermore, the addition of Pb was found to decrease the rate of hydrogen insertion. This work provides a fundamental basis for the future design of metal surfaces yielding enhanced electrochemical hydrogen insertion in Pd and other hydrogen absorbing materials.

Preparation of (FeV80)48Ti26+xCr26(x=0–4) alloys by the hydride sintering method and their hydrogen storage performance

Abstract The V-Ti-based hydrogen storage alloy (FeV80) 48 Ti 26 Cr 26 was synthesized by the hydride powder sintering method. X-ray diffraction (XRD) analysis results show that the alloy consists of a main BCC phase, a La 2 O 3 phase and a Ti-rich oxide phase. The existence of the Ti-rich oxide phase leads to a loss of Ti element content in the main BCC phase and further results in a lattice contraction. Thus, the hydrogen absorption capacity of the alloy synthesized by the hydride powder sintering method is only 2.8 wt%, with a hydrogen desorption capacity of 1.5 wt%. To address this problem, the effects of Ti element compensation on the microstructure and the hydrogen storage capacities of the alloy were investigated. It was found that the lattice constant of the BCC phase increases and the amount of Ti-rich oxide phase is almost unchanged with increased Ti element compensation, leading to an improved hydrogen storage capacity. When Ti element compensation reaches 4 at%, the hydrogen absorption capacity of the alloy reaches 3.3 wt% with a desorption capacity of 2.0 wt% at room temperature and at a pressure of 10 −4 MPa. The hydrogen desorption plateau slope factor of the (FeV80) 48 Ti 26+x Cr 26 (x = 0–4) alloy prepared by the hydride powder sintering method is as small as that of the alloy prepared by the arc-melting method. Thus the sintering method is a suitable option for the manufacture of V-Ti-based hydrogen storage alloys.

Improved Dehydrogenation Properties of 2LiNH2-MgH2 by Doping with Li3AlH6

Doping with additives in a Li-Mg-N-H system has been regarded as one of the most effective methods of improving hydrogen storage properties. In this paper, we prepared Li3AlH6 and evaluated its effect on the dehydrogenation properties of 2LiNH2-MgH2. Our studies show that doping with Li3AlH6 could effectively lower the dehydrogenation temperatures and increase the hydrogen content of 2LiNH2-MgH2. For example, 2LiNH2-MgH2-0.1Li3AlH6 can desorb 6.43 wt % of hydrogen upon heating to 300 °C, with the onset dehydrogenation temperature at 78 °C. Isothermal dehydrogenation testing indicated that 2LiNH2-MgH2-0.1Li3AlH6 had superior dehydrogenation kinetics at low temperature. Moreover, the release of byproduct NH3 was successfully suppressed. Measurement of the thermal diffusivity suggests that the enhanced dehydrogenation properties may be ascribed to the fact that doping with Li3AlH6 could improve the heat transfer for solid–solid reaction.

Highly improved hydrogen storage capacity and kinetics of the nanocrystalline and amorphous PrMg12-type alloys by mechanical milling

Nanocrystalline and amorphous PrMg11Ni + x wt.% Ni (x = 100, 200) alloys were synthesized by mechanical milling. Effects of Ni content and milling duration on the structures, hydrogen storage capacity and kinetics of the as-milled alloys were investigated systematically. The structures were characterized by XRD and HRTEM. The hydrogen desorption activation energy was calculated by using Kissinger method. The results show that increasing Ni content dramatically improves the electrochemical discharge capacity of the as-milled alloys. Furthermore, the variation of milling time has a significant impact on the kinetics of the alloys. As the milling time increased, the high-rate discharge ability (HRD), gaseous hydrogen absorption capacity and hydrogenation rate increased at first but decreased finally, while the dehydrogenation rate always increased.

Influence of nickel nanoparticles on hydrogen storage behaviors of MWCNTs

In this study, multiwalled carbon nanotube (CNT)-nickel hybrid materials were prepared from CNTs by the impregnation of nickel at various CNT/nickel mass ratios. The presence of nickel nanoparticles on CNTs influences the spillover effect on hydrogen storage capacity. A thermal reduction method was employed to increase the contacts between the nickel metal particles and the carbon support, thus facilitating hydrogen spillover. The as-obtained nickel-decorated CNTs exhibited a high hydrogen storage capacity of 0.87wt.% at 298K and 100bar, resulting in an enhancement factor of 2.5 relative to the untreated CNTs. These experimental results demonstrate that the presence of nickel creates hydrogen-favorable sites that can lead to improved hydrogen storage capacities based on the spillover effect.

Thermodynamic and electric study of the LaNi3,6Al0,4Co0,7Mn0,3 alloy

Improving hydrogen storage properties, as a very interesting energy vector, is the objective of several recent researches. AB5 compounds, whose prototype compound is LaNi5 and its derivatives, have caught the attention of many researchers especially because they have a storage reversibility of hydrogen at ambient temperature and standard pressure. This paper presents an experimental study of hydrogen storage properties and an electric study of LaNi3.6Al0.4Co0.7Mn0.3 alloy. For this reason, the equilibrium isotherms are traced at different temperatures. The effect of temperature, pressure and coolant flow on the kinetics of the hydrogen absorption was also, studies. X-ray structural analysis indicated the formation of a single-phase orthorhombic structure with lattice parameters: a = 0.7517 nm, b = 0.7459 nm and c = 0.8565 nm.Microstructural study showed a densely packed uniform distribution of grains over the surface of the sample. The Alternative current (a.c.) impedance plots were used as tools to analyze the electrical response of the sample as a function of frequency at room temperature. These plots revealed the presence of a relaxation process, which may be attributed to the same type of charge carrier. The frequency dependent conductivity was found to display the universal dynamic response behavior widely observed in disordered solid electrolytes.

Hydrogen Storage Behaviors by Adsorption on Multi-Walled Carbon Nanotubes

In the present study, MWCNTs were synthesized through CVD method, employing CH4 as carbon source over Co-Mo/MgO nanocatalyst at a temperature of 1000 °C and then treated by two methods. First by KOH activation (A-MWCNTs), with a weight ratio of KOH: MWCNTs = 3:1 at 900 °C in He atmosphere and second treated by H2SO4: HNO3 = 3:1 (F-MWCNTs). MWCNT samples were characterized by FE-SEM, TEM, XRD, FT-IR, BET and Raman spectroscopy. The adsorption of H2 gas was performed using volumetric method. Various parameters on adsorption of H2 including surface defects, surface areas, pore characteristics and functional groups have been investigated. Furthermore, it was found that the hydrogen adsorption of P-MWCNTs, A-MWCNTs and F-MWCNTs were 0.67, 1.24 and 0.40 wt%, respectively at room temperature (298 K) while the pressure varied from 0 to 34 bar. The results indicated a considerable rise in the H2 adsorption capacity of A-MWCNTs (85%), due possibly to the high surface area and enhanced micro-pore volume and the defects formed on the surface sites of MWCNTs by KOH activation. In this case, hydrogen molecules adsorption on the defective cavities could have a significant role through van der walls forces. Therefore, it can be concluded that KOH-modified MWCNTs is one of the most significant ways of developing the textural characteristic and improving hydrogen storage properly.

Hydrogenation thermokinetics and activation behavior of non-stoichiometric Zr-based Laves alloys with enhanced hydrogen storage capacity

Zr0.9−xTi0.4+xV1.7 (x = 0, 0.1) non-stoichiometric alloys are designed and expected to show improved hydrogen storage capacities of Zr-based Laves phase alloys. The samples are synthesized by arc melting followed by two different processing techniques: annealing and melt-spinning. Phase constituent and microstructure investigations reveal the multiphase structures containing C15-Laves type ZrV2, V- and Zr-based solid solutions for the annealed alloys and melt-spun ribbons. The content of ZrV2 decreases but the unit cell volume of ZrV2 increases with increasing Ti content. Activation behavior and hydrogenation kinetics at different temperatures of the annealed and melt-spun samples were studied. At 25 °C, the hydrogen absorption capacity of Zr0.8Ti0.5V1.7 reaches 2.83 wt% H. The apparent activation energies of the fast hydrogen absorption stage (α, α+β regions) are calculated to be 2–5 kJ/mol. Melt-spun ribbons exhibit higher hydrogen absorption rate and smaller hydrogen storage capacities than the annealed alloys in the initial cycle. The surface and sub-surface chemical compositions are analyzed by XPS to illustrate the influence of composition of the alloys on activation behavior. Hydrogen absorption/desorption PCT curves of the annealed samples between 400 and 550 °C were measured and allowed to derive corresponding thermodynamics parameters. The higher hydride stability of the Zr0.8Ti0.5V1.7 based hydride is related to its larger unit cell volume and higher α-Zr content as compared to Zr0.9Ti0.4V1.7.

Effects of MWCNTs on improving the hydrogen storage performance of the Li3N system

In this paper, the influence of multi-walled carbon nanotube (MWCNT)-doping on the hydrogen storage properties of the Li3N system was systematically investigated. Compared with the pure Li3N sample, the MWCNT-doped Li3N sample shows faster hydrogen absorption and desorption kinetics and a drastically improved cycling stability. Along with increasing MWCNT content, the hydrogen storage improvement becomes more apparent. When the MWCNT doping level reaches 10 mol%, the enhancement effect is significant. The improved hydrogen storage properties of the Li3N system by MWCNT-doping can be reduced to the physical effect of ball milling, the increased specific surface area and large pores as well as the good thermal conductivity of MWCNTs.

Hydrogen storage in a layered flexible [Ni2(btc)(en)2]n coordination polymer

[Ni2(btc)(en)2]n coordination polymer exhibits a layered two-dimensional structure with weak interaction between the layers. Correlation of experimental measurements, DFT calculations and molecular simulations demonstrated that its structural features, primarily the inherent flexibility of the layered polymeric structure, lead to improved hydrogen storage performance at room temperature, due to significant enhancement in isosteric heats of hydrogen adsorption. Volumetric measurements of hydrogen adsorption at room temperature show up to 0.3 wt.% hydrogen absorbed at 303 K and 2.63 bar of hydrogen pressure, with isosteric heats of adsorption of about 12.5 kJ mol−1. Predicted performance at room temperature is 1.8 wt.% at 48 bar and 3.5 wt.% at 100 bar, better than both MOF-5 and NU-100, with calculated values of isosteric heats for adsorption of hydrogen in 8–13 kJ mol−1 range at both 77 K and 303 K. Grand canonical Monte Carlo calculations show that this material, at 77 K, exhibits gravimetric hydrogen densities of more than 10 wt.% (up to 8.3 wt.% excess) with the corresponding volumetric density of at least 66 gL−1, which is comparable to MOF-5, but achieved with considerably smaller surface area of about 2500 m2 g−1. This study shows that layered two-dimensional MOFs could be a step towards MOF systems with significantly higher isosteric heats of adsorption, which could provide better room temperature hydrogen storage capabilities.