嵌入配位不饱和金属位对多孔芳香骨架材料储氢性能的影响

基于密度泛函理论(DFT)和巨正则蒙特卡洛(GCMC)模拟方法，系统地研究了引入配位不饱和金属位(CUS)对PAF-30n (n = 1–4)材料储氢性能影响的规律。结果表明，77 K下PAF-302MgO₂_PBE100的最大过量质量储氢量达到7.97% (w)；77 K、10 MPa下100%醇镁功能化改性PAF-302和PAF-303的绝对储氢量分别达到9.9% (w) (65.9 g?L^-1)和15.0% (w) (50.5 g?L^-1)，分别超过美国能源部(DOE)标准80% (64.8%)和173% (26.3%)，均超过在相同条件下目前储氢性能最佳的NU-1101 (9.1% (w), 46.6 g?L^-1)。即使在243 K、10 MPa下，其绝对质量和绝对体积储氢量也能分别达到5.13% (w)和34.19 g?L^-1，占DOE质量与体积储氢标准的93.3%和85.5%，是目前为止常温储氢性能较为均衡的多孔材料之一。结合等量吸附热(Q_st)、径向分布函数(RDF)和质心几率密度分布(MCPD)方法进一步分析，发现有机链长度增加导致孔隙率增加和体积比表面积减小，是引起多孔材料绝对质量和绝对体积储氢量此消彼长的根本原因。另外，引入CUS能提高PAFs材料对H₂分子亲和力，显著增强其体积储氢量。

Effect of Coordinatively Unsaturated Metal Sites in Porous Aromatic Frameworks on Hydrogen Storage Capacity

The effect of inserting coordinatively unsaturated metal sites (CUS) into porous aromatic frameworks (PAFs) on their hydrogen storage capacity was investigated systematically by density functional theory and grand canonical Monte Carlo simulations. The results indicate that the maximum excess gravimetric uptake of hydrogen possible with PAF-302MgO₂_PBE100 is 7.97% (w) at 77 K. The total uptakes of hydrogen by PAF-302 and PAF-303 functionalized with 100% magnesium alkoxide at 77 K and 10 MPa were determined to be 9.9% (w) (65.9 g?L^-1) and 15.0% (w) (50.5 g?L^-1), respectively. These uptake values are 80% (64.8%) and 173% (26.3%), respectively, more than the gravimetric and volumetric targets set by the Department of Energy (DOE) of USA. They also exceed the targets set by NU-1101, presenting the highest measured performance of 9.9% (w) (46.6 g?L^-1) under the same conditions. Even at 243 K and 10 MPa, the total gravimetric and volumetric uptakes of hydrogen in the former are up to 5.13% (w) and 34.19 g?L^-1, which are about 93.3% and 85.5% of the targets set by DOE, respectively. By analyzing the isosteric heat of adsorption (Q_st), radial distribution function, and mass center probability density, it is found that increasing the length of the organic linkers of PAFs incorporated with CUS will result in decreasing volumetric surface areas in spite of the increase in void fractions, which is the root of trade-offs between the total gravimetric and volumetric H₂ uptake in porous materials. Additionally, CUS incorporation improves the affinity of PAF materials to H₂ molecules, resulting in an enhancement of the volumetric hydrogen storage capacity.