Modification And Mechanism Of Zr-based Nanoalloys For High Capacity Hydrogen Storage Material MgH₂

Fuel cell technology is rapidly becoming practical.Great achievements have been made in the application of fuel cell devices on ships.The submarine using fuel cell hybrid power has been put into operation.In addition,with the increase of shipping pressure,fuel cell and hydrogen energy technologies are expected to enter the shipbuilding field and further develop to reduce harmful emissions.The future of the maritime and transport industry can be green and sustainable through fuel cell and hydrogen technologies.In the application of fuel cell,hydrogen storage technology,as a new research direction,has received extensive attention.Mg has high hydrogen storage capacity,good reversibility and low cost,which has great commercial potential.However,the practical application of MgH₂ still faces various challenges.Based on the extensive summary of previous studies,ZrMn₂,ZrCo and Zr_0.4Ti_0.6Co nano-alloys were successfully prepared by simple wet chemical ball milling to further explore the modification effect of high-efficiency catalysts on MgH₂.The effects of ZrMn₂,ZrCo and Zr_0.4Ti_0.6Co on the microstructure,de/hydrogenation performance and kinetic properties of MgH₂ were investigated in detail by XRD,SEM,TEM,DSC and Sievert hydrogen absorption performance tests.The main work are as follows:The effects of ZrMn₂ nanoparticles on the microstructure and hydrogen storage properties of MgH₂ were investigated.Experiments show that the addition of ZrMn₂nanoparticles can significantly improve the hydrogen absorption and desorption properties of MgH₂.The MgH₂ composite doped with 10 wt%ZrMn₂ started to release hydrogen at 181.9°C.At 300°C,the MgH₂ composite doped with 10wt%ZrMn₂ can release 6.7 wt%of hydrogen within 5 min.More significantly,the dehydrogenated composite can absorb hydrogen at 3 MPa H₂ and room temperature.In addition,compared with pure MgH₂,the dehydrogenation and rehydrogenation activation energy of MgH₂ composite doped with 10wt%ZrMn₂ were reduced to 82.2±2.7 kJ/mol and 22.1±2.7 kJ/mol,respectively.TEM analysis showed that the ZrMn₂ nanoparticles were uniformly distributed in the MgH₂ matrix.Density functional theory calculations further demonstrate that the presence of ZrMn₂promotes the cleavage of Mg-H bonds,and the hydrogen absorption and desorption properties of MgH₂ are significantly improved.Secondly,the effects of ZrCo nanosheets on the microstructure and hydrogen storage properties of MgH2 were investigated.The results show that the MgH2composite modified by adding 10 wt%ZrCo nanosheets can desorb about 6.3 wt%H₂in 5 min at 300°C,and can absorb 4.4 wt%H₂ in 10 min at 120°C and 3 MPa hydrogen pressure.The dehydrogenation and rehydrogenation activation energies of MgH₂+10 wt%ZrCo composites were calculated to be 90.4±1.6 kJ/mol and 57.6±1.0 kJ/mol,respectively,which reasonably explained the significant improvement of MgH₂ de/hydrogenation performance.XRD and TEM results show that with the addition of ZrCo,the diffusion of hydrogen in the composite becomes easier.ZrCo nanosheets act as a“hydrogen pump”to help hydrogen diffuse at the interface of the Mg/MgH₂.What's more,graphene can effectively improve the cycle performance of the composite,so that the hydrogen capacity of the composite system tends to be stable.Based on the previous chapter where graphene effectively guarantees hydrogen capacity,the Zr was partly substituted by Ti and the MgH₂+10wt%Zr_0.4Ti_0.6Co/5wt%CNTs composite was designed to increase the hydrogen storage performance of MgH₂.Experiments show that the MgH₂ system doped with 10 wt%Zr_0.4Ti_0.6Co nanosheets and 10wt%Zr_0.4Ti_0.6Co/5wt%CNTs has the same dehydrogenation rate.Based on the requirements for good cycling performance,the MgH₂+10wt%Zr_0.4Ti_0.6Co/5wt%CNTs composite system was further studied.Due to the presence of 10wt%Zr_0.4Ti_0.6Co and 5wt%CNTs,the dehydrogenation and rehydrogenation activation energy of MgH2 were reduced to 70.5±7.8 kJ/mol and 35.8±3.8 kJ/mol,respectively.The dual efficacy of Zr_0.4Ti_0.6Co and carbon nanotubes makes MgH₂have sustainable catalytic activity after repeated cycles,so it has high practical value.