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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]

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]