Motivated by the recent report on penta-MgN₈ sheet [Mater. Today Phys. 2023, 38, 101259] that is the first realization of type-5 pentagonal 2D tessellation with exposed regularly distributed Mg ions, we carried out density functional theory studies on the interactions of H₂ molecules with 1D penta-nanotube, 2D penta-sheet, and 3D porous structures based on penta-MgN₈. We found that when the penta-MgN₈ sheet is assembled to a 3D porous structure or curved to a nanotube, the bandgap increases from 1.18 to 1.35 and 1.88 eV, and the resulting derivatives are stable dynamically. When H₂ molecules are introduced, the nanotube behaves best in adsorption, where each Mg ion can adsorb three H₂ molecules: two on the outer surface and one on the inner surface. The curved geometry of the nanotube makes the Mg ion on the outer surface more exposed as compared with the situations of the 2D sheet and 3D porous structure, resulting in stronger adsorptions to H₂. The gravimetric capacity (volumetric capacity) is 4.25 wt % (63 g/L) and 4.25 wt % (65 g/L) for the studied penta-sheet and penta-nanotube, and the corresponding desorption temperature is 115 and 162 K at 1 atm pressure, respectively, while for the 3D porous structure, the adsorption performance is poor due to the limited space and the less curvature, leading to strong steric hindrance and less exposed configuration for Mg ions. Moreover, the effects of temperature and pressure on adsorption are also discussed.

中文翻译：

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5 型 Penta-MgN8 片、纳米管和 3D 多孔结构上的氢吸附


受到最近关于五镁氮化物 ₈ 片材的报告的启发 [Mater.今天物理。 2023, 38, 101259]首次实现了暴露规则分布的Mg离子的5型五边形二维镶嵌，我们对H ₂ 分子与一维五纳米管的相互作用进行了密度泛函理论研究、2D 五片和基于五-MgN ₈ 的 3D 多孔结构。我们发现，当五元MgN ₈ 片组装成3D多孔结构或弯曲成纳米管时，带隙从1.18增加到1.35和1.88 eV，并且所得导数是动态稳定的。当引入H ₂ 分子时，纳米管的吸附性能最好，每个Mg离子可以吸附3个H ₂ 分子：两个在外表面，一个在内表面。与2D片材和3D多孔结构的情况相比，纳米管的弯曲几何形状使得外表面的Mg离子更加暴露，从而导致对H ₂ 更强的吸附。所研究的五片和五纳米管的重量容量（体积容量）分别为 4.25 wt%（63 g/L）和 4.25 wt%（65 g/L），相应的解吸温度在 1 时分别为 115 和 162 K。分别为大气压，而对于3D多孔结构，由于空间有限和曲率较小，吸附性能较差，导致镁离子的空间位阻较强，暴露构型较少。此外，还讨论了温度和压力对吸附的影响。