Effects Of 2-methylnaphthalene Carbonization Product And Metal Oxides On Hydrogen Storage Properties Of MgH₂

In order to improve the hydrogen absorption and desorption performance of MgH₂hydrogen storage material,in this paper,carbonation product of 2-methylnaphthalene and metal oxides are used as additives to prepare three hydrogen storage composite materials by sintering method and hydrogenation ball milling method.Then,we studied their hydrogen storage performance.The mechanism of action of different additives on the hydrogen absorption and desorption performance of MgH₂ was analyzed.Mg-carbonation of 2-methylnaphthalene was synthesized by co-sintering2-methylnaphthalene and pure Mg.The characterization results show that a large amount of amorphous carbonation product is uniformly distributed in the prepared composite material.The hydrogen absorption and desorption performance test shows that Mg-carbonation of 2-methylnaphthalene can absorb 4.28 wt.%H₂ at 423 K.At 623 K,the dehydrogenation capacity of Mg-carbonation of 2-methylnaphthalene is 4.91 wt.%.The activation energy of Mg-carbonation of 2-methylnaphthalene is 104.09 k J/mol,which is61.26 k J/mol lower than that of milled MgH₂.The initial dehydrogenation temperature of Mg-carbonation of 2-methylnaphthalene is 90 K lower than that of milled MgH₂.which means that the thermodynamic property is greatly improved.Through high-temperature hydriding pure Mg and Ce_0.75Zr_0.25O₂?pure Mg and Fe_0.2Ti_0.8O₂ respectively,we prepared Mg-Ce_0.75Zr_0.25O₂ and Mg-Fe_0.2Ti_0.8O₂ composites.The hydrogen absorption capacities of Mg-Ce_0.75Zr_0.25O₂ and Mg-Fe_0.2Ti_0.8O₂composites at 373 K are 5 and 4 times of that of milled MgH₂,respectively.The activation energies of the two composites are 44.3 k J/mol and 65.72 k J/mol lower than that of milled MgH₂,respectively.The results show the additions of Ce_0.75Zr_0.25O₂ and Fe_0.2Ti_0.8O₂could reduced the initial dehydrogenation temperature of milled-Mg by 90 K and 110 K,respectively.It can be seen from JMA formula fitting that hydrogen absorption of the above composite materials show lower growth dimension n and higher reaction constant k,which means H₂ has lower nucleation dimension and faster growth rate in composites compared with milled MgH₂.It is considered that amorphous carbonation product in Mg-carbonation of 2-methylnaphthalene can greatly reduce the agglomeration of milled Mg and provide more defects and active sites for hydrogen storage.In Mg-Ce_0.75Zr_0.25O₂ and Mg-Fe_0.2Ti_0.8O₂ composites,the additive can not only prevent the agglomeration of milled Mg,but also provide the affinity of metal ions for hydrogen and the strong interaction between metal oxides/metal hydrides/pure Mg,which have important contributions to improve the hydrogen storage performance of pure Mg.