TiF3 catalyzed MgH2 as a Li/Na ion battery anode

MgH₂ has been considered as a potential anode material for Li ion batteries due to its low cost and high theoretical capacity. However, it suffers from low electronic conductivity and slow kinetics for hydrogen sorption at room temperature that results in poor reversibility, cycling stability and rate capability for Li ion storage. This work presents a MgH₂–TiF₃@CNT based Li ion battery anode manufactured via a conventional slurry based method. Working with a liquid electrolyte at room temperature, it achieves a high capacity retention of 543 mAh g^?1 in 70 cycles at 0.2 C and an improved rate capability, thanks to the improved hydrogen sorption kinetics with the presence of catalytic TiF₃. Meanwhile, the first realization of Na ion uptake in MgH₂ has been evidenced in experiments.     

TiF4-doped Mg(AlH4)2 with significantly improved dehydrogenation properties

A significant decrease in the dehydrogenation temperature of Mg(AlH₄)₂ was achieved by low-energy ball milling with TiF₄. Approximately 8.0 wt% of hydrogen was released from the Mg(AlH₄)₂-0.025TiF₄ sample with an on-set temperature of 40 °C, which represents a decrease of 75 °C relative to pristine Mg(AlH₄)₂. In contrast to the three-step reaction for pristine Mg(AlH₄)₂, hydrogen desorption from the TiF₄-doped sample involves a two-step process because the Ti-based species participates in the dehydrogenation reaction. The presence of TiF₄ alters the nucleation and growth of the dehydrogenation product, significantly decreasing the activation energy barrier of the first step in the dehydrogenation of Mg(AlH₄)₂. Further hydrogenation measurements revealed that the presence of the Ti-based species was also advantageous for hydrogen uptake, as the on-set hydrogenation temperature was only 100 °C for the dehydrogenated TiF₄-doped sample, compared with 130 °C for the additive-free sample.     

MgH2–TiF4-MWCNTs based hydrogen storage tank with central tube heat exchanger

Improvement of hydrogen sorption kinetics of MgH₂–TiF₄-MWCNTs based tank by addition of central tube heat exchanger and enhancement of hydrogen diffusion is proposed. After doping with TiF₄ and MWCNTs, dehydrogenation temperature of MgH₂ decreases significantly (ΔT = up to 90 °C). Superior hydrogen permeability, favoring hydrogen sorption kinetics is detected at hydrogen supply side to the middle of the tank, while effective heat transfer during exothermic hydrogenation is assured by the temperature increment of heat exchanger fluid (compressed air at room temperature). Hydrogen desorption and absorption can be completed within 120–150 and 25 min, respectively, up to twice as fast as the tank without heat exchanger from the previous studies. Due to fast hydrogenation rate resulting in short reaction time at high equilibrium temperature (up to 390 °C), particle agglomeration and/or sintering of MgH₂ upon cycling are prevented. Enhanced de/rehydrogenation rates and suppression of MgH₂ particle growth during cycling yield to considerable reversibility upon 20 de/rehydrogenation cycles with storage capacity up to 5.60 wt % H₂ (82% theoretical value). By increasing operating temperature to 330–335 °C, hydrogen released with constant flow rate of 0.30 standard L/min is prolonged up to three times, favoring electrical power production of PEMFC stack. Electrical performances obtained from PEMFC stack (13 single cells) supplied with hydrogen gas from MgH₂-based tank are also investigated.     

Influence of K2TiF6 additive on the hydrogen sorption properties of MgH2

In this study, the hydrogen storage properties of MgH₂ with the addition of K₂TiF₆ were investigated for the first time. The temperature-programmed desorption results showed that the addition of 10 wt% K₂TiF₆ to the MgH₂ exhibited a lower onset desorption temperature of 245 °C, which was a decrease of about 105 °C and 205 °C compared with the as-milled and as-received MgH₂, respectively. The dehydrogenation and rehydrogenation kinetics of 10 wt% K₂TiF₆-doped MgH₂ were also significantly improved compared to the un-doped MgH₂. The results of the Arrhenius plot showed that the activation energy for the hydrogen desorption of MgH₂ was reduced from 164 kJ/mol to 132 kJ/mol after the addition of 10 wt% K₂TiF₆. Meanwhile, the X-ray diffraction analysis showed the formation of a new phase of potassium hydride and titanium hydride together with magnesium fluoride and titanium in the doped MgH₂ after the dehydrogenation and rehydrogenation process. It is reasonable to conclude that the K₂TiF₆ additive doped with MgH₂ played a catalytic role through the formation of active species of KH, TiH₂, MgF₂ and Ti during the ball milling or heating process. It is therefore proposed that this newly developed product works as a real catalyst for improving the hydrogen sorption properties of MgH₂.     

Nanocrystalline structure and electrochemical hydrogen storage properties of the as-milled Mg–V–Ni–Fe–Zn-based materials

Among the electrode materials for Ni-MH batteries, the Mg alloy electrodes such as MgNi, Mg₂Ni, REMg₁₂, La₂Mg₁₇ are considered the most suitable anode materials due to their high discharge capacity and low cost. However, the poor electrochemical cycling stability prevents its practical application. In this paper, Mg_50-xV_xNi₄₅Fe₃Zn₂ (x = 0, 1, 2, 3, 4) + 50 wt% Ni alloys were prepared by partially replacing Mg with V and using mechanical ball milling techniques with amorphous and nanocrystalline structures. Electrochemical tests showed that the ball-milled alloy had good electrochemical uptake and release performance. The maximum release performance is achieved in the first cycle. After that, the discharge level and cycle stability increased significantly with increasing ball grinding time and V content.     

Synergistic effect of TiF3@ graphene on the hydrogen storage properties of Mg–Al alloy

Mg–Al alloy was prepared by sintering and mechanical alloying, and the effects of graphene (Gp), TiF₃ and Gp/titanium (III) fluoride (TiF₃) on the hydrogen storage properties of the Mg–Al alloy were studied. The results show that Gp and TiF₃ could improve the hydrogen storage properties of Mg–Al alloy. In particular, Gp and TiF₃ showed good synergistic effect for enhancing the hydrogen storage properties of Mg–Al alloy. For example, when 1.0 wt% of H₂ was absorbed/desorbed, the hydrogen adsorption/desorption temperature of the Mg–Al alloy and Mg–Al-M (M = Gp, TiF₃, and TiF₃@Gp) composites were 241/343 °C, 185/310 °C, 229/292 °C and 159/280 °C, respectively. For the Mg–Al alloy, the apparent activation energy was 176.5 kJ mol^?1, and it decreased to 139.8 kJ mol^?1, 171.6 kJ mol^?1, and 94.3 kJ mol^?1, with the addition of Gp, TiF₃ and TiF₃@Gp composites, respectively. Evidently, the comprehensive hydrogen storage properties of Mg–Al alloy were improved remarkably under the synergistic effect of Gp and TiF₃.     

Hydrogen storage properties of Mg–TM–La (TM = Ti,Fe, Ni) ternary composite powders prepared through arc plasma method

For the first time, Mg based Mg–Transition metal (TM) –La (TM = Ti, Fe, Ni) ternary composite powders were prepared directly through arc plasma evaporation of Mg–TM–La precursor mixtures followed by passivation in air. The composition, phase components, microstructure and hydrogen sorption properties of the composite powders were carefully investigated. Composition analyses revealed a reduction in TM and La contents for all powders when compared with the compositions of their precursors. It is observed that the composites are all mainly composed of ultrafine Mg covered by nano La₂O₃ introduced during passivation. Based on the Pressure–Composition–Temperature measurements, the hydrogenation enthalpies of Mg are determined to be −68.7 kJ/mol H₂ for Mg–Ti–La powder, −72.9 kJ/mol H₂ for Mg–Fe–La powder and −82.1 kJ/mol H₂ for Mg–Ni–La powder. Meantime, the hydrogen absorption kinetics can be significantly improved and the hydrogen desorption temperature can be reduced in the hydrogenated ternary Mg–TM–La composites when compared to those in the binary Mg–TM or Mg–RE composites. This is especially true for the Mg–Ni–La composite powder, which can absorb 1.5 wt% of hydrogen at 303 K after 3.5 h. Such rapid absorption kinetics at low temperatures can be attributed to the catalytic effects from both Mg₂Ni and La₂O₃. The results gathered in this study showed that simultaneous addition of 3d transition metals and 4f rare earth metals to Mg through the arc plasma method can effectively alter both the thermodynamic and kinetic properties of Mg ultrafine powders for hydrogen storage.     

Effects of Ti-based catalysts and synergistic effect of SWCNTs-TiF3 on hydrogen uptake and release from MgH2

The present investigations are focused on the effect of different Ti-based catalysts (Ti, TiO₂, TiCl₃ and TiF₃) on de/re-hydrogenation characteristics of nanocrystalline MgH₂. Desorption temperature of milled MgH₂ lowers from 380 to 350, 340, 310 and 260 °C with the addition of Ti, TiO_2, TiCl₃ and TiF₃ respectively. The rehydrogenation characteristics are also improved through the deployment of Ti-based catalysts. Among all Ti based additives, TiF₃ is found to be the most effective catalyst for hydrogen sorption from nano MgH₂. The better catalytic effect of TiF₃ over other Ti-based catalyst can be explained on the basis of temperature programmed reduction (TPR) studies. TPR experiments performed for different Ti additives, reveals that there is no oxidation/reduction reaction below 400 °C except for TiF₃. The TPR profile of TiF₃ shows some oxidation/reduction reaction exhibits at 200 °C. In order to further improve the sorption characteristics and cyclability of TiF₃ catalyzed nano MgH₂, we have investigated the effect of SWCNTs in MgH₂+TiF₃ sample. De/rehydrogenation characteristics reveal the synergistic effect of SWCNTs and TiF₃ in MgH₂+TiF₃ sample. The details of the improvement in sorption behavior of MgH₂–TiF₃ in presence of SWCNTs are described and discussed.     

Improved hydrogen storage properties of Mg-based nanocomposite by addition of LaNi5 nanoparticles

Mg (200 nm) and LaNi₅ (25 nm) nanoparticles were produced by the hydrogen plasma-metal reaction (HPMR) method, respectively. Mg–5 wt.% LaNi₅ nanocomposite was prepared by mixing these nanoparticles ultrasonically. During the hydrogenation/dehydrogenation cycle, Mg–LaNi₅ transformed into Mg–Mg₂Ni–LaH₃ nanocomposite. Mg particles broke into smaller particles of about 80 nm due to the formation of Mg₂Ni. The nanocomposite showed superior hydrogen sorption kinetics. It could absorb 3.5 wt.% H₂ in less than 5 min at 473 K, and the storage capacity was as high as 6.7 wt.% at 673 K. The nanocomposite could release 5.8 wt.% H₂ in less than 10 min at 623 K and 3.0 wt.% H₂ in 16 min at 573 K. The apparent activation energy for hydrogenation was calculated to be 26.3 kJ mol⁻¹. The high sorption kinetics was explained by the nanostructure, catalysis of Mg₂Ni and LaH₃ nanoparticles, and the size reduction effect of Mg₂Ni formation.     

Effect of CO on hydrogen storage performance of 2LiNH2 + MgH2 system

(2LiNH₂ + MgH₂) system is one of the most promising hydrogen storage materials due to its suitable operation temperature and high reversible hydrogen storage capacity. In studies and applications, impurities such as CO, CO₂, O₂, N₂ and CH₄ are potential factors which may influence its performance. In the present work, hydrogen containing 1 mol% CO is employed as the hydrogenation gas source, and directly participates in the reaction to investigate the effect of CO on the hydrogen sorption properties of (2LiNH₂ + MgH₂) system. The results indicate that the hydrogen capacity of the (Mg(NH₂)₂ + 2LiH) system declines from 5 wt.% to 3.45 wt.% after 6 cycles of hydrogenation and dehydrogenation, and can not restore to its initial level when use purified hydrogen again. The hydrogen desorption kinetics decreases obviously and the dehydrogenation activation energy increases from 133.35 kJ/mol to 153.35 kJ/mol. The main reason for these is that two new products Li₂CN₂ and MgO appear after (2LiNH₂ + MgH₂) react with CO. They are formed on the surface of materials particles, which may not only cause a permanent loss of NH²⁻, but also prevent the substance transmission during the reaction process. After re-mechanically milling, both kinetics and dehydrogenation activation energy can be recovered to the initial level.     

Hydrogen sorption kinetics of MgH2 catalyzed with titanium compounds

Identification of effective catalyst is a subject of great interest in developing MgH₂ system as a potential hydrogen storage medium. In this work, the effects of typical titanium compounds (TiF₃, TiCl₃, TiO₂, TiN and TiH₂) on MgH₂ were systematically investigated with regard to hydrogen sorption kinetics. Among them, adding TiF₃ leads to the most pronounced improvement on both absorption and desorption rates. Comparative studies indicate that the TiH₂ and MgF₂ phases in situ introduced by TiF₃ fail to explain the superior catalytic activity. However, a positive interaction between TiH₂ and MgF₂ is observed. Detailed comparison between the effect of TiF₃ and TiCl₃ additive suggests the catalytic role of F anion. XPS examination reveals that new bonding state(s) of F anion is formed in the MgH₂ + TiF₃ system. On the basis of these results, we propose that the substantial participation of F anion in the catalytic function contributes to the superior activity of TiF₃.     

Effects of compaction pressure and graphite content on hydrogen storage properties of Mg(NH2)2–2LiH hydride

Preparation of hydride–graphite compacts serves as an effective method to improve the volumetric hydrogen storage density and the effective thermal conductivity for light complex hydrides. This paper presents the effects of compaction pressure and expanded natural graphite (ENG) content on the hydrogen storage properties of the Mg(NH₂)₂–2LiH–0.07KOH compacts. The results show that the hydrogen desorption kinetics of the 1st sorption cycle decreases with the increase of the compaction pressure. However, the compacts exhibit the similar hydrogen desorption kinetics and capacities from the 2nd sorption cycles on regardless of the compaction pressure. The ENG addition significantly enhances the desorption kinetics because of the improvement of the heat transfer performance of the hydride. Furthermore, the volumetric hydrogen storage density of the hydride reaches 47 g/L after the compaction at 365 MPa, but it reduces by increasing the ENG content.     

Hydrogen storage property improvement of La–Y–Mg–Ni alloy by ball milling with TiF3

Ball milling the powders of Mg-based alloys with transition metal compounds is effective for improving their hydrogen storage performances. In this experiment, the alloys of La_1.7Y_0.3Mg₁₆Ni + x wt.% TiF₃ (x = 0–10) were prepared through mechanical milling technology. XRD, SEM, HRTEM and granulometry were used to measure the composition and microstructure of alloys. The isothermal hydrogen storage property was measured by a Sievert apparatus. The results reveal that the TiF₃ additive in ball-milled samples transforms into MgF₂ and TiH₂ after the first hydrogen absorption. Adding TiF₃ enhances the crystallinity and reduces the average particle and crystallite sizes of alloys, which is beneficial to accelerating hydriding and dehydriding kinetics. Adding 7 wt% TiF₃ into alloy decreases the dehydrogenation activation energy from 72.2 to 64.0 kJ/mol and improves the hydrogen absorption rate at low temperatures, absorbing 3.50 wt% H in 0.5 min at 323 K.     

Significant effect of TiF3 on the performance of 2NaAlH4+Ca(BH4)2 hydrogen storage properties

Titanium fluoride (TiF₃) is doped into the reactive hydride composite of 2NaAlH₄ + Ca(BH₄)₂ by ball milling to enhance the hydrogen storage properties of the composite system. NaAlH₄ and Ca(BH₄)₂ phases were fully transformed to Ca(AlH₄)₂ and NaBH₄ phases after the ball-milling process (6 h). Four major stages were discovered in the undoped and TiF₃-doped system, which is corresponding to; (i) Ca(AlH₄)₂, (ii) CaAlH₅, (iii) CaH₂ and (iv) NaBH₄, respectively. The addition of TiF₃ to the studied composite resulted in both reduced decomposition temperature and enhanced sorption kinetics compared with the undoped composite. The onset desorption temperature was reduced from 125 °C to 60 °C for the first stage in the TiF₃-doped composite, compared with the undoped composite. From differential scanning calorimetry analysis, the decomposition temperature for all stages has shifted to a lower temperature after doping with TiF₃. The activation energy has greatly reduced by 63.6 and 21.9 kJ/mol for CaAlH₅ and NaBH₄ stages, respectively, as compared with the undoped 2NaAlH₄ + Ca(BH₄)₂ composite. During the dehydrogenation process, the formation of new active species of Al₃Ti together with CaF₂ played a vital role in accelerating the reactions in 5 wt% TiF₃ doped to the studied composite system.     

Effects of TiF3 addition on the hydrogen storage properties of 4MgH2 + Cd composite

In this paper, the best performance of the MgH₂ destabilized system with different ratios of Cd (1:1, 2:1, 3:1 and 4:1) have been studied for the first time. Remarkable enhancements on the onset dehydrogenation temperature, as well as the isothermal de/rehydrogenation kinetics were shown by the 4MgH₂ + Cd composite. In order to improve the hydrogen storage properties of the 4MgH₂ + Cd, TiF₃ was added and its catalytic effects were investigated. Temperature programmed dehydrogenation result had revealed that the onset dehydrogenation temperature was improved once the 10 wt% TiF₃ was incorporated into the 4MgH₂ + Cd system. The absorption and desorption kinetics were also improved compared to the un-doped 4MgH₂ + Cd composite system. The scanning electron microscope result had displayed that the 4MgH₂ + Cd + 10 wt% TiF₃ had the smallest particle size compared to the pure and the ball-milled MgH₂, as well as the 4MgH₂ + Cd composite system. The X-ray diffraction results had demonstrated the formation of an intermediate compound, Mg₃Cd, which was formed during the heating process. For the TiF₃-doped sample, it is reasonable to conclude that the in-situ formed TiH₂ and F-containing species play a synergetic role to encourage interactions between the MgH₂ and the Cd and thus further ameliorate the performances of the hydrogen storage of 4MgH₂ + Cd composite system.     

The destabilization of LiBH4 through the addition of Bi2Se3 nanosheets

Efficient storage of hydrogen is a key issue to establish hydrogen infrastructure. In the efforts of searching suitable hydrogen storage alloys, several systems have been explored so far. All of them suffers from some drawbacks such as low gravimetric capacity, high stability, slow sorption kinetics, etc. Lithium borohydride (LiBH₄) is one of the leading contender among the hydrogen storage materials owing to its high hydrogen content of 18.5 wt%. However, its high stability needs a high operating temperature (>450 °C) for the decomposition. Recently, a thermochemical reaction between Bi₂X₃ and LiBH₄ was observed at 120 °C while performing experiments on the anode properties of Bi₂X₃ (X = S, Se, & Te) for Li-ion batteries. This indicated the possibility of destabilization of LiBH₄ and its low-temperature decomposition. This work presents the effect of Bi₂Se₃ addition to the decomposition properties of LiBH₄ using XRD and XPS techniques. The first step decomposition was observed to be initiated at around 180 °C, which is much lower than 450 °C for the pristine LiBH₄. A further reduction in the onset temperature is observed when the bulk Bi₂Se₃ is replaced by the nanosheets of this material. The mechanism of this destabilization is reported herein.     

SOC-dependent high-rate dischargeability of AB5-type metal hydride anode: Mechanism linking phase transition to electrochemical H-desorption kinetics

The current application of nickel-metal hydride (Ni-MH) batteries places a particular emphasis on the high-rate dischargeability (HRD) at varying state-of-charges (SOCs). However, most research on the HRD of AB₅-type MH anodes only considers the fully charged case but overlooks the significant impact of SOC. In this work, at first, the great SOC effect on the HRD or pulse power of AB₅-type MH anode is presented. Then, by crosschecking the SOC dependence of both ‘in situ’ polarization and ‘ex situ’ kinetic parameters, a definite SOC-dependent H-desorption kinetics for AB₅-type MH anode is acquired. Finally, a novel mechanism linking phase transition to H-desorption kinetics for AB₅-type MH anode is proposed. The HRD or pulse power of AB₅-type MH anode significantly improves when SOC decreases from 100% to an appropriate range (90-60%) and suddenly deteriorates when SOC drops below ∼20%. The former improvement relates to the formation of saturated solid solution that simultaneously facilitates both charge-transfer reaction and hydrogen diffusion. The latter deterioration is due to the complete depletion of hydride causing an insufficient supply of hydrogen atoms.     

Efficient hydrogen storage with the combination of metal Mg and porous nanostructured material

High-energy density and low cost magnesium nanoparticles (Mg NPs)-based material are being sought to meet increasing capable of hydrogen (H₂) storage demand. Here, a kind of air-stable Mg NPs supported on porous structured multi-walled carbon tubes-polymethyl methacrylate (MWCNTs-PMMA) template is prepared owing to reversible well-distributed, dispersed and small-sized Mg/MgH₂ NPs. The aim is to improve the H₂ storage capacity, hydrogen sorption kinetics and thermodynamics of nano Mg-based system without using catalyst. The organic Mg precursor was directly in-situ reduced to metallic Mg NPs in MWCNTs-PMMA template by lithium naphthalide. The size distribution of reduced Mg nanoparticles is around 3.6 ± 0.2 nm, confirmed by XRD and TEM analyses, which is due to the strong interaction between Mg NPs and MWCNTs-PMMA via PMMA binding Mg²⁺, as well as the confinement of porous template hindered the growth and agglomeration of Mg NPs. Moreover, except H₂, O₂ and H₂O molecules can't infiltrate the porous structure of MWCNTs-PMMA resulted in the presence of air stable Mg NPs in the MWCNTs-PMMA. The work provides a new scope to prepare nano metal-based composite for H₂ storage.     

The role of Al2Ca and Al2(Sm,Ca,La) particles in the microstructures and electrochemical discharge performance of as‐extruded Mg‐3wt.%Al‐1wt.%Zn‐based alloys for primary Mg‐air batteries

In this work, the role of Al₂Ca and Al₂(Sm,Ca,La) particles in the microstructures and electrochemical discharge performance of the as‐extruded Mg‐3wt.%Al‐1wt.%Zn‐based alloys has been reported and discussed for the anode design of Mg‐air batteries. The Al₂Ca and Al₂(Sm,Ca,La) particles strongly refine the grains of the as‐extruded AZ31 alloy from 9.1 ± 4.1 μm down to 5.1 ± 3.3 μm. The Al₂Ca and Al₂(Sm,Ca,La) particles increase the outputting cell voltage and discharge capacity of the modified AZ31 alloy. The AZ31‐Ca alloy exhibits the highest discharge capacity and anodic efficiency of 1153 mAh/g and 52.5%, respectively, at 10 mA/cm². The promoted discharge performance should be mainly attributed to the grain refinement (improving the corrosion resistance) and fine Al₂Ca phase throughout the matrix (beneficial for uniform dissolution of Mg phase). Additional Al₂(Sm,Ca,La) cubic particles further stimulate the anodic kinetics and aggravate the local dissolution of Mg phase near around, resulting in the deterioration of discharge performance.     

Improved hydrogen storage performance of MgH2–NaAlH4 composite by addition of TiF3

In a previous paper, it was demonstrated that a MgH₂–NaAlH₄ composite system had improved dehydrogenation performance compared with as-milled pure NaAlH₄ and pure MgH₂ alone. The purpose of the present study was to investigate the hydrogen storage properties of the MgH₂–NaAlH₄ composite in the presence of TiF₃. 10 wt.% TiF₃ was added to the MgH₂–NaAlH₄ mixture, and its catalytic effects were investigated. The reaction mechanism and the hydrogen storage properties were studied by X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry (DSC), temperature-programmed-desorption and isothermal sorption measurements. The DSC results show that MgH₂–NaAlH₄ composite milled with 10 wt.% TiF₃ had lower dehydrogenation temperatures, by 100, 73, 30, and 25 °C, respectively, for each step in the four-step dehydrogenation process compared to the neat MgH₂–NaAlH₄ composite. Kinetic desorption results show that the MgH₂–NaAlH₄–TiF₃ composite released about 2.4 wt.% hydrogen within 10 min at 300 °C, while the neat MgH₂–NaAlH₄ sample only released less than 1.0 wt.% hydrogen under the same conditions. From the Kissinger plot, the apparent activation energy, E_A, for the decomposition of MgH₂, NaMgH₃, and NaH in the MgH₂–NaAlH₄–TiF₃ composite was reduced to 71, 104, and 124 kJ/mol, respectively, compared with 148, 142, and 138 kJ/mol in the neat MgH₂–NaAlH₄ composite. The high catalytic activity of TiF₃ is associated with in situ formation of a microcrystalline intermetallic Ti–Al phase from TiF₃ and NaAlH₄ during ball milling or the dehydrogenation process. Once formed, the Ti–Al phase acts as a real catalyst in the MgH₂–NaAlH₄–TiF₃ composite system.