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Due to its high hydrogen storage efficiency and safety, Mg/MgH2 stands out from many solid hydrogen storage materials and is considered as one of the most promising solid hydrogen storage materials. However, thermodynamic/kinetic deficiencies of the performance of Mg/MgH2 limit its practical applications for which a series of improvements have been carried out by scholars. This paper summarizes, analyzes and organizes the current research status of the hydrogen storage performance of Mg/MgH2 and its improvement measures, discusses in detail the hot studies on improving the hydrogen storage performance of Mg/MgH2 (improvement measures, such as alloying treatment, nano-treatment and catalyst doping), and focuses on the discussion and in-depth analysis of the catalytic effects and mechanisms of various metal-based catalysts on the kinetic and cyclic performance of Mg/MgH2. Finally, the challenges and opportunities faced by Mg/MgH2 are discussed, and strategies to improve its hydrogen storage performance are proposed to provide ideas and help for the next research in Mg/MgH2 and the whole field of hydrogen storage. [ABSTRACT FROM AUTHOR]

Bimetallic catalysts offer unique advantages for improving the hydrogen storage performance of MgH2. Herein, Ni3Fe/BC nanocatalysts were prepared via a simple solid phase reduction method using a low-cost biomass charcoal (BC) material as the carrier. The onset temperature of hydrogen release for the MgH2 + 10 wt% Ni3Fe/BC composite was 184.5 °C, which is 155.5 °C lower than that of pure MgH2. The dehydrogenated composite starts to absorb hydrogen at as low as 30 °C and is able to absorb 5.35 wt% of H2 within 10 min under 3 MPa hydrogen pressure at 150 °C. In comparison to pure MgH2, the apparent activation energies of dehydrogenation and rehydrogenation of MgH2 + 10 wt% Ni3Fe/BC were reduced by 52.89 kJ mol−1 and 23.28 kJ mol−1, respectively. The hydrogen storage capacity of the composite was maintained in 20 de/rehydrogenation cycles, indicating a good cycling stability. X-Ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray energy dispersive spectroscopy (EDS) characterization reveal that the in situ formation of multiphases Mg2Ni and Fe catalysts during the hydrogen uptake and release reaction and the transformation of Mg2Ni/Mg2NiH4 together contribute to the superior hydrogen adsorption and desorption performance of MgH2. [ABSTRACT FROM AUTHOR]

Bimetallic catalysts offer unique advantages for improving the hydrogen storage performance of MgH2. Herein, Ni3Fe/BC nanocatalysts were prepared via a simple solid phase reduction method using a low-cost biomass charcoal (BC) material as the carrier. The onset temperature of hydrogen release for the MgH2 + 10 wt% Ni3Fe/BC composite was 184.5 °C, which is 155.5 °C lower than that of pure MgH2. The dehydrogenated composite starts to absorb hydrogen at as low as 30 °C and is able to absorb 5.35 wt% of H2 within 10 min under 3 MPa hydrogen pressure at 150 °C. In comparison to pure MgH2, the apparent activation energies of dehydrogenation and rehydrogenation of MgH2 + 10 wt% Ni3Fe/BC were reduced by 52.89 kJ mol−1 and 23.28 kJ mol−1, respectively. The hydrogen storage capacity of the composite was maintained in 20 de/rehydrogenation cycles, indicating a good cycling stability. X-Ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray energy dispersive spectroscopy (EDS) characterization reveal that the in situ formation of multiphases Mg2Ni and Fe catalysts during the hydrogen uptake and release reaction and the transformation of Mg2Ni/Mg2NiH4 together contribute to the superior hydrogen adsorption and desorption performance of MgH2. [ABSTRACT FROM AUTHOR]

Transition metal catalysts are particularly effective in improving the kinetics of the reversible hydrogen storage reaction for light metal hydrides. Herein, K2MoO4 microrods were prepared using a simple evaporative crystallization method, and it was confirmed that the kinetic properties of magnesium hydride could be adjusted by doping cubic K2MoO4 into MgH2. Its unique cubic structure forms new species in the process of hydrogen absorption and desorption, which shows excellent catalytic activity in the process of hydrogen storage in MgH2. The dissociation and adsorption time of hydrogen is related to the amount of K2MoO4. Generally speaking, the more K2MoO4, the faster the kinetic performance and the shorter the time used. According to the experimental results, the initial dehydrogenation temperature of MgH2 + 10 wt% K2MoO4 composite is 250 °C, which is about 110 °C lower than that of As-received MgH2. At 320 °C, almost all dehydrogenation was completed within 11 min. In the temperature rise hydrogen absorption test, the composite system can start to absorb hydrogen at about 70 °C. At 200 °C and 3 MPa hydrogen pressure, 5.5 wt% H2 can be absorbed within 20 min. In addition, the activation energy of hydrogen absorption and dehydrogenation of the composite system decreased by 14.8 kJ/mol and 26.54 kJ/mol, respectively, compared to pure MgH2. In the cycle-stability test of the composite system, the hydrogen storage capacity of MgH2 can still reach more than 92% after the end of the 10th cycle, and the hydrogen storage capacity only decreases by about 0.49 wt%. The synergistic effect among the new species MgO, MgMo2O7, and KH generated in situ during the reaction may help to enhance the absorption and dissociation of H2 on the Mg/MgH2 surface and improve the kinetics of MgH2 for absorption and dehydrogenation. [ABSTRACT FROM AUTHOR]

Carbon materials play an important role in the development of solid hydrogen storage materials. The main purpose of this work is to study the low-cost synthesis of biomass carbon (BC) and its positive effect on the hydrogen storage behavior of magnesium hydride (MgH2). Herein, it is proven that when biomass carbon (BC) is used together with magnesium hydride (MgH2), biomass carbon can be used as an adsorption and desorption channel for hydrogen. The initial dehydrogenation temperature of MgH2 + 10 wt% BC composite is 250 °C, which is 110 °C lower than that of pure MgH2. In addition, the MgH2 + 10 wt% BC composite system can complete all dehydrogenation processes within 10 min at 350 °C. Meanwhile, 5.1 wt% H2 can also be dehydrogenated within 1 h at 300 °C. Under the same conditions, MgH2 hardly starts to release hydrogen. After complete dehydrogenation, the composite can start to absorb hydrogen at 110 °C. Under the conditions of 225 °C and 3 MPa, 6.13 wt% H2 can be absorbed within 1 h, basically reaching the theoretical dehydrogenation limit. Cycling experiments show that the MgH2 + 10 wt% BC composite has a good stability. After 10 cycles, the hydrogen storage capacity shows almost no obvious decline. It is believed that this study can help in the research and development of efficient carbon-based multifunctional catalysts. [ABSTRACT FROM AUTHOR]

In this study, a low-cost biomass charcoal (BC)-based nickel catalyst (Ni/BC) was introduced into the MgH 2 system by ball-milling. The study demonstrated that the Ni/BC catalyst significantly improved the hydrogen desorption and absorption kinetics of MgH 2. The MgH 2 + 10 wt% Ni/BC-3 composite starts to release hydrogen at 187.8 °C, which is 162.2 °C lower than the initial dehydrogenation temperature of pure MgH 2. Besides, 6.04 wt% dehydrogenation can be achieved within 3.5 min at 300 °C. After the dehydrogenation is completed, MgH 2 + 10 wt% Ni/BC-3 can start to absorb hydrogen even at 30 °C, which achieved the absorption of 5 wt% H 2 in 60 min under the condition of 3 MPa hydrogen pressure and 125 °C. The apparent activation energies of dehydrogenation and hydrogen absorption of MgH 2 + 10 wt% Ni/BC-3 composites were 82.49 kJ/mol and 23.87 kJ/mol lower than those of pure MgH 2 , respectively, which indicated that the carbon layer wrapped around MgH 2 effectively improved the cycle stability of hydrogen storage materials. Moreover, MgH 2 + 10 wt% Ni/BC-3 can still maintain 99% hydrogen storage capacity after 20 cycles. XRD, EDS, SEM and TEM revealed that the Ni/BC catalyst evenly distributed around MgH 2 formed Mg 2 Ni/Mg 2 NiH 4 in situ, which act as a "hydrogen pump" to boost the diffusion of hydrogen along with the Mg/MgH 2 interface. Meanwhile, the carbon layer with fantastic conductivity enormously accelerated the electron transfer. Consequently, there is no denying that the synergistic effect extremely facilitated the hydrogen absorption and desorption kinetic performance of MgH 2. The carbon layer is evenly wrapped around MgH 2 /Mg, and Ni nano catalyst is evenly distributed on the surface. During dehydrogenation and reabsorption, Ni nanoparticles generate Mg 2 Ni and Mg 2 NiH 4 in situ. The use of uniformly distributed Mg 2 Ni/Mg 2 NiH 4 as a "hydrogen pump" promotes the diffusion of hydrogen along the Mg/MgH 2 interface, and the carbon layer with good conductivity accelerates the electron transfer. It is believed that the synergistic effect of the two improves the hydrogen absorption and desorption rate of MgH 2. [Display omitted] • Biomass charcoal was introduced into the MgH 2 system for the first time. • Composites started to release H 2 at 187.8 °C and could start to absorb H 2 at 30 °C. • The activation energy of de/hydrogenation was significantly reduced for composites. • Biomass charcoal contributes to the cyclic stability of composites. [ABSTRACT FROM AUTHOR]

The development of high-efficiency carbon-based multifunctional catalysts is of great significance for improving solid-state hydrogen storage materials. Herein, it was confirmed that CoMoO 4 sheet-like nanocatalysts uniformly supported on the surface of reduced graphene oxide (CoMoO 4 /rGO) were successfully prepared by a simple hydrothermal reaction. The novel CoMoO 4 /rGO catalyst was subsequently doped into MgH 2 to improve its hydrogen storage performance. MgH 2 –10 wt% CoMoO 4 /rGO starts to release hydrogen at around 204 °C, which is about 36 °C and 156 °C lower than that of MgH 2 −10 wt%CoMoO 4 and pure MgH 2 , respectively. In addition, 6.25 wt% H 2 can be released within 10 min at 300 °C. After complete dehydrogenation, H 2 can be absorbed below 80 °C. Meanwhile, it can absorb 4.2 wt% H 2 in 20 min under the condition of 150 °C and 3 MPa. Moreover, the activation energy of hydrogen absorption and dehydrogenation of MgH 2 –10 wt%CoMoO 4 /rGO composites are reduced by 31.44 kJ mol−1 and 33.78 kJ mol−1, respectively, compared with pure MgH 2. Cycling experiment shows that the MgH 2 –10 wt%CoMoO 4 /rGO composite system can still maintain about 98% of the hydrogen storage capacity after 10 cycles. Furthermore, studies on the catalytic mechanism show that the synergistic effect between the in-situ generated MgO, Co 7 Mo 6 and Mo may help to promote the diffusion of H 2 , thereby improving the MgH 2 Hydrogen storage properties. • MgH 2 –10 wt%CoMoO 4 /rGO composite system was reported for the first time. • MgH 2 –10 wt%CoMoO 4 /rGO composite material starts dehydrogenation at about 204 °C. • MgH 2 –CoMoO 4 /rGO composites showed promising kinetic properties. • MgH 2 –CoMoO 4 /rGO composites showed good cyclic stability. • MgO, Mo and Co 7 Mo 6 were formed in situ during the reaction. [ABSTRACT FROM AUTHOR]

• The fibrous spherical NiMoO4 increases the number of catalytic active sites. • Hydrogen could be released at 191 °C and absorbed at 50 °C for the composite. • De/hydrogenation activation energy of the composite were significantly reduced. • The existence of rGO maintains the stability of the cycle. The synergistic catalysis has a good improvement on the hydrogen storage properties of MgH 2. In this work, fibrous spherical NiMoO 4 bimetallic catalysts were prepared by hydrothermal and sintering methods, and introduced into the MgH 2 system by ball milling to improve their kinetic performance. In addition, rGO (reduced graphene oxide) was also introduced to improve the cycling stability of MgH 2. It is observed that NiMoO 4 has a significant improvement in the kinetics of MgH 2 absorption and dehydrogenation. MgH 2 + 10 wt% NiMoO 4 can start dehydrogenation at 191 °C. After complete dehydrogenation, it starts to absorb hydrogen below 50 °C. The apparent activation energy of dehydrogenation and hydrogen absorption of MgH 2 + 10 wt% NiMoO 4 composites were reduced by 35.43 kJ mol−1 and 30.10 kJ mol−1, respectively, compared with pure MgH 2. The results of characterization indicated that the uniformly dispersed NiMoO 4 produced Mg 2 Ni and elemental Mo in situ after the first hydrogen release reaction. It is believed that the synergistic effect of Mo and Ni elements accelerates the hydrogen absorption and desorption performance of hydrogen storage materials. Cycling performance tests showed that the addition of rGO improved the cycling stability of the hydrogen storage material. Mg 2 Ni/Mg 2 NiH 4 and Mo promote the desorption and diffusion of H in the process of hydrogen absorption and desorption. In addition, Mo element can also effectively promote the mutual conversion of Mg 2 Ni/Mg 2 NiH 4. The synergistic effect of Mo and Ni can accelerate the de/rehydrogenation performance of hydrogen storage materials. The existence of rGO maintains the stability of the cycle. [Display omitted] [ABSTRACT FROM AUTHOR]

At present, catalyst doping has been widely concerned by researchers as an effective method to improve the hydrogen storage performance of MgH 2. Herein, it is confirmed that MnMoO 4 rod catalyst can effectively improve the hydrogen storage performance of MgH 2. According to the experimental results, MgH 2 +10 wt%MnMoO 4 composite material starts dehydrogenation at about 220 °C, which is about 140 °C lower than MgH 2 without additives. The initial dehydrogenation capacity of 6 wt% can be reached within 10min at 300 °C. After complete dehydrogenation, H 2 can be absorbed below 55 °C, and 4.34 wt% H 2 can be absorbed within 15 min at 150 °C and 3 MPa hydrogen pressure. In addition, the activation energy of dehydrogenation of MgH 2 decreased about 45 kJ mol−1. Furthermore, hydrogen storage capacity of MgH 2 can still be maintained at 5.85 wt% after 20 cycles. The synergy between the in-situ formed Mn and MgMo 2 O 7 may help promote the dissociation and diffusion of H 2 along the Mg/MgH 2 interface, thereby improving the hydrogen storage performance of MgH 2. [Display omitted] • MgH 2 –MnMoO 4 composite system was reported for the first time. • MgH 2 +10 wt%MnMoO 4 composite material starts dehydrogenation at about 220 °C. • MgH 2 –MnMoO 4 composites showed promising kinetic properties. • MgO, Mn and MgMo 2 O 7 were formed in situ during the reaction. [ABSTRACT FROM AUTHOR]

• Nano NiO/C catalysts were prepared by ultrasonic oscillation and calcination. • Hydrogen could be released at 195 °C and absorbed at 50 °C for the composite. • De/hydrogenation activation energy of the composite were significantly reduced. • The composite material had good cyclic reversibility. • Ab initio calculations showed that NiO and Mg 2 Ni could improve the diffusivity of H atoms. Magnesium based solid hydrogen storage material (MgH 2) has the advantages of good safety and high hydrogen storage capacity in the shipping field. However, the high hydrogen absorption and desorption temperature have not been well solved. Herein, this work proves that it is very effective to improve the hydrogen storage performance of MgH 2 by doping nano NiO/C catalyst. Specifically, experimental results showed that MgH 2 + 9 wt% NiO/C composite could dehydrogenate at 195 °C, which was 155 °C lower than pure MgH 2. In addition, 6.21 wt% H 2 could be released rapidly at 300 °C for 10 min. After complete dehydrogenation, the absorption rate of hydrogen is 50 °C, which is 80 °C lower than that of pure MgH 2. Moreover, 5.13 wt% H 2 could be absorbed within 1 h at 125 °C and 3 MPa hydrogen pressure. In addition, dehydrogenation and hydrogen absorption apparent activation energies of MgH 2 + 9 wt% NiO/C composite are 70.26 kJ/mol and 25.55 kJ/mol lower than those of pure MgH 2 , respectively. The cycle experiment showed that MgH 2 + 9 wt% NiO/C had excellent cycle stability and could maintain 98.8% hydrogen storage capacity after 20 cycles. Furthermore, the study of the catalytic mechanism indicated that NiO/C catalyst is evenly distributed on the surface of MgH 2. More importantly, Mg 2 Ni/Mg 2 NiH 4 is generated in situ, which acts as a "hydrogen pump" and speeds up hydrogen diffusion during the hydrogen absorption and desorption cycle. [ABSTRACT FROM AUTHOR]