Study On Modification Of Hydrogen Storage Property Of Mg-Al Alloy By Reduction Of Graphene Oxide Loading

Based on the high hydrogen storage capacity of both magnesium and aluminum and their complementary advantages in thermodynamic properties.Therefore,in this paper,Mg-Al alloy was prepared by sintering and mechanical alloying,and modified by reducing graphene oxide supported rare earth oxides and transition metals.The details are as follows:Firstly,the rGO and CeO₂@rGO catalysts were prepared by hydrothermal reduction method.And then the 5 wt.%rGO,5 wt.%CeO₂,5 wt.%CeO₂@rGO composites were introduced to Mg95Al5 alloy by ball milling and their effect on the hydrogen absorption and desorption kinetics and thermodynamic properties of Mg95Al5 alloy were studied.It was found that the hydrogenation temperature of Mg95Al5 alloy and Mg95Al5+M?M=rGO,CeO₂,CeO₂@rGO?composites was 138.1 ?,122.4 ?,55.6 0C,46.4 ?,respectively,when absorbed 1.0 wt.%of H2.After modified by rGO,CeO₂ and CeO₂@rGO composite,the temperature was reduced by 15.7 ?,82.5 ?,and 91.7 ?,respectively.When released 1.0 wt.%of H2,the temperatures of Mg95Al5 alloy and Mg95Al5+M?M=rGO,CeO₂,CeO₂@rGO?were 294.2 ?,281.1 ?,239.1 ? and 242.1 ?,respectively.After the addition of rGO,Ce02 and Ce02@rG0 composites,the desorption temperature of the Mg95Al5 alloy reduced by 13.1 ?,55.1 ? and 52.1 ?,respectively.The main phase for the Mg-Al hydride was MgH2,and dehydrogenation production for all the samples was only Mg and H2,indicating that rGO,CeO₂ and CeO₂@rGO only play a catalytic role in the hydrogenation and dehydrogenation processes.The dehydrogenation activation energies of Mg95Al5+M?M=rGO,Ce02,Ce02@rG0?were 177.2 kJ/mol,172.1 kJ/mol,85.3 kJ/mol,83.8 kJ/mol,respectively.Secondly,the La₂O₃@rGO composite also was prepared by chemical precipitation method,and the rGO,La₂O₃ and La₂O₃@rGO were used as catalysts.The 5 wt.%rGO,5 wt.%La₂O₃,5 wt.%La₂O₃@rGO were added to catalyze Mg95Al5 alloy before the alloy was wet milling in the tetrahydrofuran for 80 h,and study its effect on the hydrogen absorption/desorption kinetics and thermodynamic properties of Mg95Al5 alloy.When absorbed 2.0 wt.%of H2,the Mg95Al5 alloy needed to heated to 155.9 ?,and this temperature droped to 141.3 ?,134.3 ?,73.9 ?,respectively,under the catalyst action of the rGO,La₂O₃ and La₂O₃@rGO composite.It reduced by 14.6 ?,21.6 ?,and 82 ?.In addition,when released 2.0 wt.%of H2,the temperatures of Mg95Al5 alloy and Mg95Al5+M?M=rGO,La203,La203@rGO?were 302.5 ?,289.7 ?,299.4 ?and 260.6 ?,respectively.The main phase formed after hydrogenation is MgH2,and the main phase formed after dehydrogenation is Mg,indicating that rGO,La₂O₃,and La₂O₃@rGO only play a catalytic role in the hydrogenation and dehydrogenation processes.The hydrogen activation energies of Mg95Al5 alloy and Mg95Al5+M?M=rGO,La₂O₃,La₂O₃@rGO?were calculated by Kissinger equation to be 177.2 kJ/mol,172.1 kJ/mol,237.4 kJ/mol and 167.8 kJ/mol,respectively.Finally,the Ni@rGO and Pd@rGO were prepared by hydrothermal reduction method,and the rGO,Ni@rGO and Pd@rGO were used as catalysts.The 5 wt.%rGO,5 wt.%Ni@rGO,5 wt.%Pd@rGO were added to catalyze Mg95Al5 alloy?wet milling in the tetrahydrofuran for 80 h?,and study its effect on the hydrogen absorption and desorption kinetics and thermodynamic properties of Mg95Al5 alloy.It was found that the maximum hydrogen absorption capacity of Mg95Al5 alloy and Mg95Al5+M?M=rG0,Ni@rGO,Pd@rGO?is 5.58 wt.%,6.14 wt.%,5.26 wt.%,5.11 wt.%,And the hydrogen absorption rate of Mg95Al5+rGO sample is the fastest,while the hydrogen absorption curves of the other three samples are basically coincident.The maximum hydrogen release amount of Mg95Al5 alloy and Mg95Al5+M?M=rGO,Ni@rGO,Pd@rGO?is 5.26 wt.%,5.51 wt.%,5.02 wt.%,4.88 wt.%.The hydrogen release curves of the three samples of Mg95Al5+M?M=rGO,Ni@rGO,Pd@rGO?were basically coincident,while the hydrogen release temperature of the Mg95Al5 alloy sample was the highest.The main phase formed after hydrogenation is MgH2,and the main phase formed after dehydrogenation is Mg,indicating that rGO,Ni@rGO and Pd@rGO only play a catalytic role in the hydrogenation and dehydrogenation processes.The hydrogen release activation energies of Mg95Al5 alloy and Mg95Al5+M?M=rGO,Ni@rGO,Pd@rGO?were 177.2 kJ/mol,172.1 kJ/mol,106.5 kJ/mol and 130.5 kJ/mol,respectively,calculated by Kissinger equation.