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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]

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]

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]