Table 1

Comparison of gas, liquid and solid hydrogen storage methods"

Fig.1

Common crystal structures of magnesium hydride [33]"

Fig.2

The corresponding P-T phase diagram of MgH2 [33]"

Fig. 3

(a)Pressure component isotherm diagram of Mg/MgH2 and (b)Van′ t Hoff diagram corresponding to the Mg/MgH2 phase transition[38]"

Fig.4

The hydrogen absorption content obtained from the PC isotherms of different Mg-Ni system alloys at 373 K[51]"

Fig.5

DSC curves of Mg100-x Ni x (x=0, 5, 10 and 20) alloys after HCS+MM[52]"

Fig.6

(a) DSC and (b) TPD curves of Mg80Ni20H x before and after exposure for 15 days, 4 and 10 months, isothermal (c) hydrogenation and (d) dehydrogenation curves of Mg80Ni20H x before and after air exposure for 4 months, (e) JMAK fitting plots and (f) Arrhenius plot of air-exposed Mg80Ni20H x for the dehydriding kinetics [53]"

Table 2

Hydrogen storage capacity and dehydrogenation enthalpy of some binary magnesium alloys"

Fig. 7

Hydrogenation and dehydrogenation curves of the Mg-Al and Mg-Al-TM(TM=Ti、Ni、V)alloys[60]"

Fig. 8

Arrhenius plots of the Mg95-x Al5Y x (x=0~5)[61]: (a)Y0 alloys; (b)Y1 alloys; (c)Y2 alloys; (d)Y3 alloys; (e)Y4 alloys and (f)Y5 alloys"

Fig. 9

Isothermal hydrogen absorption curves of the activated Mg95-x Ni x Y5(x=5, 10, 15)samples in different temperatures: (a)Mg90Ni5Y5; (b)Mg85Ni10Y5; (c)Mg80Ni15Y5 and (d)the comparison of hydrogen absorption rate of these samples at optimum hydrogenated temperature [63]"

Fig. 10

200-cycle dehydrogenation performance diagram of Mg91Ni9 and Mg91Ni8La1 [65]"

Table 3

Corresponding hydrogen storage parameters of some magnesium alloys"

Fig.11

Hydrogen absorption curves of Mg x TiVNiAlCr(x=0, 0.5, 1)at 473 K, 523 K, 573 K [75]"

Fig. 12

Comparison between the variation of the reversible hydrogen storage capacity during cycling for the quinary Mg0.1Ti0.3V0.25Zr0.1Nb0.25 and quaternary Ti0.325V0.275Zr0.125Nb0.275 alloys [76]"

Fig. 13

Schematic of the catalytic mechanism and cycle properties of the nano-MgH2-Ni system [87]"

Fig. 14

Diagram of the catalytic mechanism of MgC0.5Co3[89]"

Fig. 15

Diagram of the mechanism of hydrogen storage under air exposure of Mg NCs/PMMA [95]"

Fig. 16

TEM micrographs for the cross section of (a) Pd (25 nm)/Mg (200 nm) and (b) Pd (50 nm)/Mg (200 nm)/Pd (50 nm) films [101]"

Fig. 17

Hydrogen absorption of Mg-PMMA nanocomposites containing 33.2%, 49%, 54.7%, 58.2% and 65% Mg [106]"

Fig. 18

Preparation process, catalytic phase characterization, and cycling performance diagram of MgH2@CoS-NBs [109]"

Table 4

Performance differences and technical difficulties of MgH2 prepared by different methods"

Fig. 19

TEM image of the Mg-Ti nanopowder [114]"

Fig. 20

TGA profiles of the hydrogenated products of the Mg-Ti nanopowder(A)MgH2-5%Ti(CVS); (B)commerical MgH2; (C)MgH2-5%Ti(milled)[114]"

Fig. 21

Thermal desorption mass spectra of hydrogen from the MgH2 composite with 1?mol% Ni by milling for 15?min, 1?h, and 2?h at 400?r/min under a hydrogen gas atmosphere of 1?MPa [115]"

Fig. 22

Hydrogen desorption curves of the (a) MgH2 milled for 2 h； (b) MgH2+10%Ni； (c) MgH2+25% Ni； (d) MgH2+50% Ni, and (e) MgH2+80% Ni at 523 K under an initial pressure of 0.01bar of H2[116]"

Fig. 23

Comparison of the effects of different Ni particle sizes on the desorption properties of pre-milled MgH2 by simply mixed 20 h-pre-milled MgH2 and different types Ni (90 nm, 100 nm, 200 nm and 7 μm)[117]"

Fig. 24

The adsorption geometry of MgH2 on Fe (110)surface in top view (a); The brown, green, and white ball represent Fe, Mg, and H, respectively, The projected density of states (PDOS)of Mg and H of MgH2 before (upper)and after (lower)adsorption on Fe (110)surface (b) [108]"

Fig. 25

Schematic diagram of the hydrogenation and dehydrogenation mechanisms of MgH2/TiO2 heterostructure[127]"

Fig. 26

(a)Temperature-programmed-desorption and (b) isothermal dehydrogenation curves at 275 ℃ of MgH2, MgH2-5%Ni/Al2O3 and MgH2-5%NiO/Al2O3 ; isothermal dehydrogenation curves of (c)MgH2-5%NiO/Al2O3 and (d)MgH2-5%Ni/Al2O3 at different temperatures of 250 ℃, 275 ℃ and 300 ℃; (e)the corresponding solid-state reaction mechanism model and rate-controlling step of MgH2-5%Ni/Al2O3; (f)time dependence of the kinetic modeling equation F(α)and the plot for the temperature-dependent rate constant k, obtained by the Arrhenius equation[128]"

Fig. 27

Schematic diagram of the microstructural evolution for the MgH2@5%Sc2O3/TiO2 composite during the hydrogenation-dehydrogenation process [130]"

Fig. 28

XRD patterns of MgH2+7% LiCoO2 composite: after ball milling, after dehydrogenation and after rehydrogenation [131]"

Fig. 29

(a)Isothermal dehydrogenation curves of MgH2-6 wt% MnCo2O4.5 and (c)as-milled MgH2; (b)isothermal hydrogenation curves of MgH2-6 wt% MnCo2O4.5 and (d)as-milled MgH2; (e)de/hydrogenation cycle curves of MgH2-6 wt% MnCo2O4.5 at 325 ℃, and (f)decay curves of hydrogen storage capacity[120]"

Table 5

Hydrogen storage properties of some MgH2- ternary transition metal oxides"

Fig. 30

XRD patterns of MgH2+5%K2NiF6 composite: after ball milling, after dehydrogenation and after rehydrogenation [144]"

Fig. 31

Schematic illustration of the catalytic mechanism of the K2TaF7-catalyzed MgH2 composite[145]"

Fig. 32

Schematic diagram of the hydrogenation/dehydrogenation processes of the MgH2-FeNi2S4 composite [147]"

Fig. 33

Isothermal hydriding curves of the Mg, Mg/ZIF-8, Mg/ZIF-67, and Mg/MOF-74composites [154]: (a)hydrogenation process at 175 ℃; (b)dehydrogenation process at 300 ℃"

Fig. 34

(a)Typical bright field TEM micrograph; (b)the corresponding SAED pattern; (c)、(d)the HRTEM images, (e)—(i)the dark field micrographs and the corresponding elemental mappings of MgH2-5% Ni-MOF after 11th hydrogenation[155]"

Fig. 35

Isothermal hydrogenation/dehydrogenation curves of MgNb and MgNb/ZIF-67 nanocomposites at (a)175 ℃ and (b)275 ℃ [156]"

Fig. 36

(a)、(b) SEM micrographs of the Mg and MgNb/ZIF-67 nanocomposites (c)—(e)TEM images and SAED of MgNb/ZIF-67 after 100 hydrogen absorption/desorption cycles[156]"

Fig. 37

The mechanism diagram and corresponding dehydrogenation curve of MgH2 improved by Nb2O5 and MOF [157]"

Table 6

Summary of hydrogen storage properties of MgH2 modified by some other metal compounds"

Fig. 38

Schematic illustration for the “bidirectional catalysis” mechanism of Co/Pd@B-CNTs on the dehydrogenation and hydrogenation of MgH2[164]"

Fig. 39

Schematic diagram of the catalytic mechanism of catalysts during the hydrogenation/dehydrogenation processes of the MgH2-5 wt%Ni3ZnC0.7/Ni@CNT nanocomposite[165]"

Fig. 40

The corresponding lnk vs 1000/T plots for hydrogenated (a) and dehydrogenated (b) MgH2-xNZC/Ni@CNT (x=2.5%, 5%, 7.5%)composites. Comparison of TPD curves (c) of MgH2-xNZC/Ni@CNT (x=2.5%, 5%, 7.5%)and MgH2[165]"

Fig. 41

(a) enthalpy change of graphene-doped Mg4H8 dehydrogenation and (b) activation energy of MgH2 [166]"

Fig. 42

Adsorption dehydrogenation curves of MgH2 and MgH2+10%Fe-Ni@3DG: (a) isothermal hydrogen absorption; (b) isothermal dehydrogenation; (c) cyclic performance diagram of MgH2; (d) cyclic performance diagram of MgH2+10%Fe-Ni@3DG[167]"

Fig. 43

(a) Isothermal hydrogenation curves of commercial MgH2, hyd-MgBu2, and 60% MgH2@Ti-MX at 175 ℃ and (b) isothermal hydrogenation curves of 60% MgH2@Ti-MX at different temperatures; (c) cycling dehydrogenation curves of 60% MgH2@Ti-MX at 200 ℃, and (d) typical TEM image of 60% MgH2@Ti-MX after 60 de/hydrogenation cycles at 200 ℃[173]"

Fig. 44

(a) Schematic pictures showing the hydrogen desorption and absorption mechanisms of MgH2 with addition of V2C/Ti3C2 and (b) schematic diagram comparatively displaying the energy barriers for as-milled MgH2 and MgH2-V2C/Ti3C2[174]"

Table 7

Hydrogen storage performance of MgH2 modified by some metal and carbon based composite catalysts"

Fig. 45

Comparison of MgH2-5%FeCoNiCrMn and milled MgH2[180]: (a) TPD curves; (b) dehydrogenation content when heated to different temperatures; (c)、(e) isothermal dehydrogenation curves; (d)、(f) isothermal hydrogenation curves"

Fig. 46

Schematic representation of catalytic mechanism of catalyst (LHEA) during dehydrogenation of MgH2 [181]"