Effects Of Graphene Supported Metal/metal Oxide On Hydrogen Storage Properties Of Mgh₂

The preparation process and catalyst selection are important factors influencing the hydrogen storage performance of Mg and MgH2.Therefore,this paper aims to improve the hycdrogen storage performance of Mg and MgH2 by the adjustment of the preparation process and the optimized screening of the catalyst.Firstly,MgH2 powder was used as the starting material and wet-milled under argon for different time to study the effect of milling time on the hydrogen storage performance of MgH2.The results show that the ball milling of MgH2 material can significantly improve its hydrogen storage performance.After ball milling,the grain size decreased.Among them,the MgH2 sample after wet milling for 100 hours has the best hydrogen storage performance,and its maximum hydrogen release amount is 6.96 wt%.At the heating rate of 2 K·min-1,when the hydrogen absorption and desorption amount reaches 1 wt%,compared with the original MgH2 sample,the hydrogen absorption temperature decreases 153? and the hydrogen release temperature was lowered by 85 ?,the dehydrogenation peak temperature of DSC was lowered by 105?(the heating rate was 5 K·min-1).After continuously increasing the milling time,the hydrogen storage performance of MgH2 was not further improved.Secondly,the catalytic effects of composites such as Gp,Nb2O5 and Nb2O5@Gp on the hydrogen storage performance of MgH2 were studied.The results show that Gp and Nb2O5 have a good synergistic effect on improving the hydrogen storage performance of MgH2 storage.For example,when the amount of hydrogen released reaches 1 wt%,the hydrogen release temperatures of MgH2 and MgH2-M(M = Gp,Nb2O5 and Nb2O5@Gp)are 273 0C,288 ?,2690 C and 245? respectively.Graphene-supported Nb2O5(Nb2O5@Gp)can effectively reduce the hydrogen release temperature of the material and reduce the activation energy of MgH2.For example,the activation energy of MgH2 is 100.7 kJ·mol-1H2,after adding Nb2O5@Gp,the activation energy decreases to 85.3 kJ·mol-1H2,which is 15.2 kJ·mol-1H2 lower than that of pure MgH2.Finally,nano-sized magnesium hydride was prepared by hydrogenation ball milling with magnesium powder(hydrogen storage performance was different from that of wet-milled MgH2),and composite Ni@Gp were synthesized by hydrothermal method.The composite materials were prepared for MgH2 storage.The PCI test showed that at 275?,the composite MgH2-Ni@Gp was able to undergo a reversible hydrogen absorption and desorption process,under the same conditions,MgH2 could absorb hydrogen,but could not dehydrogenate.The amount of hydrogen absorption of MgH2-Ni@Gp in 4000 s at 100? was 5.48 wt%,under the same conditions,MgH2 was only 0.70 wt%.In addition,when the amount of hydrogen absorbed and discharged reaches 1 wt%,the hydrogen absorption and desorption temperatures of MgH2-Ni@Gp was 88?and 54? lower than the MgH2 respectively.The activation energies of MgH2 and MgH2-Ni@Gp were 163.9 kJ·mol-1H2 and 103.5 kJ·mol-1H2 respectively.The results show that the additional Ni@Gp nanocomposites is beneficial to improve the hydrogen storage performance of MgH2.