•Polyaniline (PANI) was used to modify the surface of Mg3MnNi2 alloy firstly.•PANI has been successfully polymerized on the surface of Mg3MnNi2 alloy particles.•Discharge capacity retention (R20) was increased obviously after PANI modification.•Modification with PANI can favor the charge-transfer reaction on the alloy surface.In this paper, polyaniline (PANI) has been adopted to modify the surface of Mg3MnNi2 hydrogen storage electrode alloy prepared by induction melting via chemical deposition. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) tests were performed to investigate the phase composition and microstructure. The comprehensive analysis based on the results of XRD, SEM, TEM and FT-IR indicates that PANI with a thickness of about 10 nm has been successfully polymerized on the surface of Mg3MnNi2 alloy. The discharge capacity retention (R20) of the Mg3MnNi2 alloy has been increased from 13.5% to 36.2% after modification with PANI, indicating better cycling stability. The Tafel polarization curves reveal that the surface modification of Mg3MnNi2 alloy with PANI can enhance its anti-corrosion ability. The increase of the exchange current density (Io) indicates that the surface activity of Mg3MnNi2 alloy can be improved through the surface modification with PANI. However, the high rate discharge ability (HRD) test shows that the kinetic property of Mg3MnNi2 alloy after the surface modification is declined, which is mainly due to the decline of the hydrogen diffusion in PANI, evidenced by the decreased limit current density (IL) obtained from the anodic polarization curves.

In this work, Mg-based hydrogen storage composites with an initial 100-x: x (x=25, 32.3, 50, 66.7) of Mg:Ni molar ratio were prepared by HCS+MM and their phase compositions and electrochemical performances were investigated in detail. The results show that the composites with desirable constituents can be achieved by adjusting the molar ratio of the starting materials in the HCS process. Particularly, the HCS product of Mg67.7Ni32.3 consists of the principal phase Mg2NiH4 and minor phase Mg2NiH0.3. The dominate phase varies from Mg2NiH0.3 and MgH2 for the Mg enriched sample (x<32.3) to MgNi2 and Ni for the Ni enriched sample (x>32.3). The MM modification not only brings about grain refinement of the alloys, but also leads to phase transformation of part Mg2NiH4 to Mg2NiH0.3 in the Mg67.7Ni32.3 sample. Electrochemical tests indicate that each sample can reach its maximum discharge capacity at the first cycle. Mg67.7Ni32.3 displays the highest discharge capacity as well as a superior electrochemical kinetics owing to its excellent H atom diffusion ability and lower charge-transfer resistance. The Mg67.7Ni32.3 provides the most optimized Mg/Ni atomic ratio considering the comprehensive electrochemical properties of all samples.

•A synthetic method of Si@porous-C was developed using nano-MgO as the pore-former.•Si nanoparticles were homogeneously embedded in porous-C with spherical space.•Si@porous-C possesses enhanced cyclic stability and high-rate capability.•The template method employed in the present work is industrially scalable.In the present work, the sample of Si nanoparticles embedded in porous C (denoted as Si@porous-C) has been successfully synthesized by using nano-MgO as the pore-former. Observations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) on Si@porous-C sample reveal that Si nanoparticles homogeneously disperse in porous carbon scaffold. As anode of lithium ion battery (LIB), Si@porous-C preserves a charge-discharge capacity of 1172 mAh g−1 after 40 cycles, possessing enhanced cyclic deterioration of only 0.35% per cycle in comparison with Si nanoparticles and Si nanoparticles embedded in ordinary carbon (denoted as Si@C). It delivers reversible capacities of about 947 mAh g−1, 670 mAh g−1, and 394 mAh g−1 in current densities of 1000 mA g−1, 2000 mA g−1, and 4000 mA g−1, respectively, all of which are higher than those of commercial nano-silicon and Si@C. The improved high-rate capability of Si@porous-C could be attributed to a decreased resistance and enhanced infiltration of electrolytic solution around nano-silicon particles. The merits of scalable synthetic process and improved electrochemical properties recommend Si@porous-C as a promising anode material for high performance Li-ion batteries.

•2LiBH4-MgH2 expressed 10 times higher conductivity than LiBH4.•2LiBH4-MgH2 possessed a window voltage of 4 V.•The lithium ionic mobility is contributed by grain boundary based on HRTEM.2LiBH4-MgH2 was employed as fast ionic conductor for the first time. The present work found that 2LiBH4-MgH2 composite offers σ of 10− 2 S cm− 1 at a temperature over 373 K, and possesses σ value 10 times higher than that of LiBH4 at a temperature below 373 K. A window voltage of 4 V can be achieved for 2LiBH4-MgH2 according to the cyclic voltammetry (CV for 5 cycles) tests. X-ray diffraction (XRD) and Fourier Transform infrared spectroscopy (FTIR) measurements on 2LiBH4-MgH2 samples milled for different time demonstrate that original phases are well preserved during ball milling and temperature ramping even after CV tests. Their chemical stabilities were also demonstrated by differential scanning calorimetry (DSC) measurements. The enhanced lithium mobility at low temperature in 2LiBH4-MgH2 should be ascribed to the favorable boundaries, in which defects and amorphous phases were clearly observed by means of high-resolution transmission electron microscope (HRTEM).2LiBH4-MgH2 was synthesized by ball-milling and employed as lithium ionic conductor. It offers conductivity of 10− 2 S cm− 1 at a temperature over 373 K, and 10 times higher than that of LiBH4 at a temperature below 373 K.Download high-res image (169KB)Download full-size image

•LixNa3-xAlH6 compounds have been successfully prepared by grinding mixtures of Li3AlH6 and Na3AlH6.•The x range in LixNa3-xAlH6 compounds is 0.9–1.3.•Both ΔHde and Ea values of Li1.3Na1.7AlH6 are the lowest in LixNa3-xAlH6 compounds.Mixed alkali alanates LixNa3-xAlH6 have been successfully synthesized by means of grinding mixtures of Li3AlH6 and Na3AlH6 in specific molar ratios. Non-stoichiometric LixNa3-xAlH6 compounds with single perovskite-type structures (space group Fm-3m) can be formed only within the composition range of x = 0.9–1.3. Li1.3Na1.7AlH6 exhibits superior hydrogen storage properties over other LixNa3-xAlH6 compounds. Its onset dehydrogenation temperature (∼423 K) was lowered by more than 40 K from other samples in temperature programmed dehydrogenation (TPD) curves. Also, the dehydrogenation capacity of Li1.3Na1.7AlH6 (3.45 wt.%) is the highest among the compounds. The dehydrogenation enthalpy values of LixNa3-xAlH6 decreased as x increased from 0.9 to 1.3 according to the results by isothermal pressure-composition (PCI) curves and van't Hoff plots. It shows that the dehydrogenation Li1.3Na1.7AlH6 (49.7 kJ mol H2−1) was greatly destabilized from that of LiNa2AlH6 (68.1 kJ mol H2−1). Furthermore, the apparent activation energy of dehydrogenation for Li1.3Na1.7AlH6 (138.1 kJ mol−1) was remarkably lowered from that of LiNa2AlH6. This illustrates that Li1.3Na1.7AlH6 exhibits enhanced dehydrogenation kinetics from that of LiNa2AlH6.

•The onset dehydrogenation temperature of LiNa2AlH6 was lowered by 68 K due to additive Ti3C2.•Ti3C2 significantly destabilized the dehydrogenation of LiNa2AlH6.•The hydrogenation kinetics of LiNa2AlH6 was slightly improved by Ti3C2.In the present work, two-dimension lamellar Ti3C2 was employed as additive of LiNa2AlH6. Volumetric dehydrogenation results informed that the onset dehydrogenation temperature of the ball milled LiNa2AlH6 + 5 wt% Ti3C2 sample was lowered by 68 K from that of pristine LiNa2AlH6. Isothermal pressure-composition (P-C-I) curves and van't Hoff plots demonstrated that the dehydrogenation enthalpy value (61 kJ mol H2−1) of LiNa2AlH6 + 5 wt% Ti3C2 was significantly reduced from the pristine LiNa2AlH6(68 kJ mol H2−1). By means of XPS analyses, it can be revealed that the destabilization of LiNa2AlH6 should be resulted from the involvement of Ti and the yield of unidentified Ti3+ species. Furthermore, it can be concluded that the lowering of dehydrogenation temperature was merely due to the thermal destabilization of LiNa2AlH6 by Ti3C2, since Ti3C2 hardly improved the dehydrogenation kinetics of LiNa2AlH6 and reduced its activation energy. However, hydrogenation kinetics was slightly enhanced from the released products of LiNa2AlH6 + 5 wt% Ti3C2.

•A novel 4LiAlH4 + Mg2NiH4 composite was synthesized.•The synergistic hydrogen desorption effect has been discovered for the first time.•Mg2NiH4 promotes decomposition of LiAlH4 in MM and thermal desorption process.•In situ formed Al can destabilize Mg2NiH4 via a new reaction pathway.•The composite shows ultrafast re-hydrogenation kinetics in initial three cycles.Mg2NiH4 was prepared by hydriding combustion synthesis (HCS) method firstly. Then, the as prepared Mg2NiH4 was mechanically milled with LiAlH4 to form a novel composite of 4LiAlH4 + Mg2NiH4. Hydrogen storage properties and reaction mechanism of the 4LiAlH4 + Mg2NiH4 composite during hydrogenation/dehydrogenation have been investigated systematically by pressure-composition-temperature (PCT), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements. The microstructure of the composite has been investigated by scanning electron microscopy (SEM). The experimental results show that there is a mutual destabilization effect between Mg2NiH4 and LiAlH4 during hydrogen desorption. Mg2NiH4 can promote the decomposition of LiAlH4 in both of the ball milling process and the thermal desorption process. Conversely, the in situ formed Al from the decomposition of LiAlH4 can destabilize Mg2NiH4 via a new reaction pathway with lower activation energy. Moreover, the 4LiAlH4 + Mg2NiH4 composite shows ultrafast re-hydrogenation kinetics, and the re-hydrogenation mechanism has been revealed.

•LiBH4-Li3N possessed higher conductivity than LiBH4 by nearly 100 times.•LiBH4-Li3N presents a window voltage of 3 V, much higher than Li3N.•The lithium ionic mobility was mainly contributed by Li3N according to 7Li NMR.The x LiBH4-Li3N (x = 1, 2, 4) composites were investigated on their lithium ionic conductivities. They maintained the original phase structures of orthorhombic LiBH4 and hexagonal β-Li3N during ball milling according to the analyses by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Electrochemical impedance spectra (EIS) tests showed that LiBH4-Li3N composites lift the lithium ionic conductivities from that of bulk LiBH4 by nearly 100 times at low temperature. LiBH4-Li3N offers 1.06 × 10− 5 S cm− 1 of conductivity while bulk LiBH4 possesses only 2.05 × 10− 7 S cm− 1 at 323 K. Cyclic voltammetry (CV) tests indicated that the voltage window of composites could attain 3 V, which is much more stable than Li3N (< 1 V). No thermodynamic incident appears in DSC curves except for the orthorhombic-hexagonal transition endothermic peak of LiBH4 in the x LiBH4-Li3N composites. It confirms the phases stabilities of the x LiBH4-Li3N (x = 1, 2, 4) composites before and after CV tests. In-situ solid state Nuclear Magnetic Resonance (NMR) tests on LiBH4-Li3N illustrated that the high conductivity in low temperature should not come from high-temperature phase of LiBH4. Therefore, the enhancement of lithium ionic mobility of the composite might be attributed to both Li3N and the interfaces between small crystallites where transmission electron microscope (TEM) morphology showed the appearance of amorphous grain boundary.

•The Mg64Pd3Co33 enhances discharge capacity of 624 mAh g−1 from Mg67Co33.•Reaction kinetics, corrosion resistance and cyclic stability were improved by Pd.•Hydroxides, surface passivation, and dissolution of Mg affected cyclic stability.The ternary Mg67−xPdxCo33 (x = 1, 3, 5, 7) alloys were prepared and served as anode materials for the Ni-MH battery system. Pd facilitates the formation of a full body-centered cubic (BCC) phase in binary Mg67Co33. All Mg67−xPdxCo33 (x = 1, 3, 5, 7) alloys possess BCC structure in nano-crystalline, which were observed by XRD and TEM analyses. In addition, their lattice parameters increase with the augmentation of Pd content. The charge–discharge experiments show that Mg64Pd3Co33 owns the maximum discharge capacity of 624 mAh g−1 among Mg67−xPdxCo33 (x = 1, 3, 5, 7) electrodes, which was greatly enhanced from our previously studied binary Mg–Co and ternary Mg–Co–Pd electrodes. All electrochemical kinetics e.g. exchange current density, hydrogen atomic diffusion capability were improved by substituting Pd for Mg, which were also relevant with the increment of Pd amount in the alloys. X-ray photoelectric spectroscopy (XPS) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) demonstrated that Pd relieved the severe corrosions and capacity degradations of the electrodes.

•The onset temperature of hydrogen release was decreased to 54 °C in 4MgH2LiAlH4TiH2 composite.•Additive TiH2 reduced the de/re-hydrogenation activation energies.•TiH2 was not involved in the reactions, but served as catalyst for composite's dehydrogenation.The hydrogen storage performance of a 4MgH2LiAlH4 composite system was greatly improved by adding TiH2. The temperature-programmed release curve of the 4MgH2LiAlH4TiH2 composite reflected that the onset temperature of dehydrogenation decreased remarkably to 54 °C from that of 4MgH2LiAlH4 (100 °C). X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses indicated that TiH2 was not involved in the decomposition of either LiAlH4 or MgH2 or their interactions. In the ternary composite, TiH2 can be regarded as an effective catalyst for LiAlH4, Li3AlH6 and MgH2, of which the activation energies of dehydrogenation were reduced by 23.3 kJ/mol, 29.1 kJ/mol and 45.5 kJ/mol from those of 4MgH2LiAlH4, respectively. The rehydrogenation of those products at 350 °C cannot be fully integrated into their original phases, and the reversible capacity was ascribed only to the formation of MgH2. The activation energy of rehydrogenation of MgH2 was greatly decreased to 108.9 kJ/mol from 158.8 kJ/mol of 4MgH2LiAlH4. Isothermal hydrogenation curves and fitted lines from the Arrhenius equation demonstrated the enhancement of hydrogenation kinetics.

•Binary MgxCo100–x alloys (x = 40, 45, 50, 55, 60, 63) with BCC structure can reversibly charge–discharge in Ni-MH battery system.•With the increase of Mg content in the alloys, electrodes discharge kinetics will be increased accordingly.•The Pd-doped ternary alloys drastically increase the discharge capacities (280–500 mAh g−1) from binary ones.•The additional Pd improves cycle stabilities, kinetics, and corrosion resistances of the alloys.In this work, a serial of Mg–Co binary alloys with body-centered cubic (BCC) phase were prepared for anode materials of Ni-MH hydrogen storage battery system. TEM/SAED analyses on binary Mg–Co alloys demonstrated that their grains were all in nano-size (∼5 nm) with BCC structure. Electrochemical tests found that, with increase of the concentration of Mg in alloys, theoretical charge–discharge capacities would increase accordingly, discharge kinetics (exchange current densities and hydrogen diffusion abilities) were improved as well. However, the tested capacity will attain a maximum value (325 mAh g−1) at the point of Mg55Co45 and deteriorate subsequently with continuous increase of Mg content, which was possibly due to the optimized lattice parameter value and Mg corrosion. The increase of Co concentration in the binary alloys effectively inhibited the corrosion of the electrodes. On the basis of Mg–Co binary alloys, the Pd-doped ternary alloys with BCC structure were also prepared by means of ball milling. These alloys possess greatly enhanced discharge capacities (280–500 mAh g−1) from binary ones. It shows that with increase of the Mg content, the discharge capacities of Mg–Co–Pd ternary alloys will increase monotonously. The additional Pd also improved cycle stabilities, kinetics, and corrosion potentials of the alloys, which was beneficial to improving the properties of Mg–Co hydrogen storage electrodes.

In order to improve the discharge capacity and cyclic life of Mg–Co-based alloy, ternary Mg45M5Co50 (M=Pd, Zr) alloys were synthesized via mechanical alloying. TEM analysis demonstrates that these alloys all possess body-centered cubic (BCC) phase in nano-crystalline. Electrochemical experiments show that Mg45Zr5Co50 electrode exhibits the highest capacity (425 mA·h/g) among the Mg45M5Co50 (M=Mg, Pd, Zr) alloys. And Mg45Pd5Co50 electrode lifts not only the initial discharge capacity (379 mA·h/g), but also the discharge kinetics, e.g., exchange current density and hydrogen diffusion ability from that of Mg50Co50. It could be concluded that the electrochemical performances were enhanced by substituting Zr and Pd for Mg in Mg–Co-based alloy.

•TiH2 and Pd synergistically enhanced the dehydrogenation performances of MgH2.•The co-additives improved the release kinetics more markedly than individual one.•Pd slightly destabilized the ternary phase system by yielding Mg6Pd.In the present work, co-additives of Pd and TiH2 synergistically enhance the dehydrogenation performance of MgH2. The volumetric release measurements on 2MgH2–TiH2–0.1Pd composite revealed that the onset temperature of the dehydrogenation (150 °C) was greatly lowered by 150 °C from that of pristine MgH2. X-ray diffraction (XRD) analyses and high-resolution transmission electron microscopy (HR-TEM) observations found that Pd decomposed the MgH2 through yielding the Mg6Pd phase. The destabilizations of MgH2 in 2MgH2–0.1Pd and 2MgH2–TiH2–0.1Pd were confirmed by calculating the slopes of Van't Hoff plots of those composites based on pressure–composition isotherms. Those composites contain two significant plateaus in P–C isotherms of dehydrogenation, one represents the 2MgH2–0.1Pd release in initial stage, the other belongs to the self-decomposition of MgH2. TiH2 did not involve in the destabilization of MgH2 in the composite. However, it remarkably reduced the activation energy of the ternary system in dehydrogenation and improved its kinetics along with Pd. The activation energy value (77 kJ mol−1) of 2MgH2–TiH2–0.1Pd was found drastically lower than those of 2MgH2–0.1Pd (254.6 kJ mol−1) and 2MgH2–TiH2 (154.2 kJ mol−1). It exhibits that the synergistic effect by co-additives of TiH2 and Pd on dehydrogenation kinetics are more remarkable than any individual one.

•Mg50Co50-based BCC alloys exhibit reversible charge–discharge capacities.•The Mg50Co45Pd5 alloy possesses the maximum discharge capacity of 458 mAh g−1.•Additive Pd enhances the discharge kinetics the Mg50Co50-based alloys.The Mg50Co50 and Mg50Pd5Co45 alloys with nano-crystalline body-centered cubic (BCC) structure were confirmed by means of XRD and TEM/SAED analyses. They are available in the anode of Ni–MH battery system, which can be reversibly charged and discharged with maximum capacity of 458 mAh g−1. They exhibit greatly enhanced reversible hydrogen storage, differing from their tough dehydrogenation performances in solid–gas system [Y. Zhang et al., Journal of Alloys and Compounds 393 (2005) 147–153]. This phenomenon can be ascribed to the structural stability of Mg50Co50-based binary and ternary BCC alloys in the electrochemical reactions, and also the electro-catalysis activity. Introducing Pd into Mg50Co50 alloy lifts not only the initial discharge capacity, but also the high-rate discharge-ability. The exchange current density and hydrogen diffusion mobility can also be improved by the Pd additive in the ternary electrode alloys.

•Mg45Pd5Ni45Zr5 alloy was prepared for the anode of Ni-MH battery.•The cycle stability of Mg45Pd5Ni45Zr5 is remarkably enhanced from that of Mg50Ni50.•The composite film on Mg45Pd5Ni45Zr5 surface can effectively suppress corrosion.The Mg50Ni50–based ternary and quaternary alloys partially substituted by Pd and/or Zr have been intensively studied on their structures and electrochemical hydrogen storage performances. The Mg45Pd5Ni50 and Mg45Pd5Ni45Zr5 alloys contained both amorphous phase and body-centered cubic phase, differing from most previously studied amorphous Mg50Ni50–based alloys. The detected lattice parameters of nano-crystalline BCC phase in Mg45Pd5Ni50 and Mg45Pd5Ni45Zr5 alloys were 0.2916 nm and 0.2933 nm, respectively. Charge-discharge tests indicated that Pd facilitates lifting the cyclic retention rate in 20 cycles (C20/Cmax) from 13.2% of Mg50Ni50 alloy to 47.3% of Mg45Pd5Ni50 alloy. The partial substitution of Zr for Ni in Mg50Ni50 alloy improved the initial capacity by 12% from that of Mg50Ni50 alloy (445 mAh g−1). Synergetic substitution of Pd and Zr in Mg50Ni50 can greatly inhibit the corrosion of Mg45Pd5Ni45Zr5 alloy. According to XPS study, the Mg, Pd, Ni and Zr on the surface of Mg45Pd5Ni45Zr5 alloy would be oxidized into MgO, PdO2, Ni2O3 and ZrO2 during charge/discharge cycles. They formed a passive composite film and therefore improved the cyclic stability.

•The dehydrogenation kinetics of the Mg(NH2)2–2LiH–0.1Mg2(BH4)2(NH2)2 was greatly enhanced from Mg(NH2)2–2LiH composite.•Its dehydrogenation was composed of a serial of reactions.•The combination of 6Mg(NH2)2–9LiH–LiBH4 dominated the hydrogen release from the system of Mg(NH2)2–2LiH–0.1Mg2(BH4)2(NH2)2.Doping Mg(NH2)2–2LiH by Mg2(BH4)2(NH2)2 compound exhibits enhanced hydrogen de/re-hydrogenation performance. The peak width in temperature-programmed desorption (TPD) profile for the Mg(NH2)2–2LiH–0.1Mg2(BH4)2(NH2)2 was remarkably shrunk by 60 °C from that of pristine Mg(NH2)2–2LiH, and the peak temperature was lowered by 12 °C from the latter. Its isothermal dehydrogenation rate was greatly improved by five times from the latter at 200 °C. XRD, FTIR and NMR analyses revealed that a series of reactions occurred in the dehydrogenation of the composite. The prior interaction between LiH and Mg–B–N–H yielded intermediate LiBH4, which subsequently reacted with Mg(NH2)2 and LiH in molar ratio of 1:6:9 to form Li2Mg2(NH)3 and Li4BN3H10 phases. The observed 6Mg(NH2)2–9LiH–LiBH4 combination dominated the hydrogen release and soak in the composite system, and enhanced the kinetics of the system.

•Ball milling Mg(NH2)2–3LiH–AB liberates of 9.6 wt% H2.•Mechanochemical reaction of Mg(NH2)2–3LiH–AB is superior to LiH–AB and Mg(NH2)2–AB.•Three dehydrogenation steps were observed during the ball milling process.•AB prone to reacts with LiH prior to Mg(NH2)2 during the ball milling process.Ball milling the mixture of Mg(NH2)2, LiH and NH3BH3 in a molar ratio of 1:3:1 results in the direct liberation of 9.6 wt% H2 (11 equiv. H), which is superior to binary systems such as LiH–AB (6 equiv. H), AB–Mg(NH2)2 (No H2 release) and LiH–Mg(NH2)2 (4 equiv. H), respectively. The overall dehydrogenation is a three-step process in which LiH firstly reacts with AB to yield LiNH2BH3 and LiNH2BH3 further reacts with Mg(NH2)2 to form LiMgBN3H3. LiMgBN3H3 subsequently interacts with additional 2 equivalents of LiH to form Li3BN2 and MgNH as well as hydrogen.

•TiH2 and Al synergistically lower the dehydrogenation temperature of MgH2.•The 17MgH2-12Al-TiH2 reduces the hydrogen release activation energy from 17MgH2-12Al.•TiH2 destabilizes the 17MgH2-12Al system above 280 °C of dehydrogenation.In this work, we introduced TiH2 into the 17MgH2-12Al composite by ball milling for improving the dehydrogenation performance of the reactive system. According to the measurements of non-isothermal dehydrogenation, the onset temperature of hydrogen release from 17MgH2-12Al-TiH2 was reduced by 50 °C from that of 17MgH2-12Al. The investigations by Kissinger's method showed that the activation energy of hydrogen desorption of 17MgH2-12Al-TiH2 (107 kJ mol−1) is much lower than 17MgH2-12Al (168 kJ mol−1), leading to enhanced dehydrogenation kinetics due to the TiH2 additive. X-ray diffraction (XRD) analysis suggests that TiH2 catalyzed the reaction between MgH2 with Al of the system during the dehydrogenation below 280 °C. At temperatures between 280 °C to 400 °C, however, TiH2 will thoroughly react with produced Mg17Al12 and liberate hydrogen. The overall reaction of the system may be represented by 17 MgH2 + 12 Al + TiH2 → 3/4 Mg17Al12 + Al3Ti + 17/4 Mg + 18 H2. Its theoretical dehydrogenation capacity (4.38 wt% H2) agrees well with that achieved by temperature programmed dehydrogenation (TPD) measurements, demonstrating the occurrence of such reaction(s). The dehydrogenation enthalpy of 17MgH2-12Al-TiH2 (71.7 kJ mol−1 H2) proceeding at lower hydrogen desorption plateau was significantly lowered from that of 17MgH2-12Al (81.9 kJ mol−1 H2) according to the measurements of pressure-composition isotherms (PCI) and van't Hoff plots. It means that TiH2 was involved in the end reaction proceeding in the 17MgH2-12Al system. We believe that TiH2 improves the dehydrogenation kinetics of 17MgH2-12Al initially and tailors its thermodynamics finally.