MIL-88A metal-organic framework with the unsaturated Fe metal coordination sites has demonstrated to be a promising material for gas storage and capture. However, the hydrogen storage capacity of MIL-88A has to be improved to meet the practical level at the ambient conditions. In this research, we elucidated the effects of transition metal substitution on the hydrogen storage capability of MIL-88A. The trivalent transition metals including Sc, Ti, V, Cr, Mn, and Ni have been selected to substitute for Fe in MIL-88A. Using the van der Waals dispersion-corrected density functional theory calculations, we explored the most favorable adsorption configurations of the hydrogen molecule in M-MIL-88A (M = Sc, Ti, V, Cr, Mn, Ni). We found that the V-MIL-88A has the strongest binding energy of 17 kJ mol⁻¹ with the hydrogen molecule in the side-on configuration on the metal site. Besides, the grand canonical Monte Carlo simulations showed that the metal substitution greatly influences not only the favorable adsorption configuration and energy but also the hydrogen uptake due to the modification of the H₂@MIL-88A interaction. Sc-MIL-88A was found to offer the highest gravimetric H₂ uptake compared to the other M-MIL-88A. The value is 5.13 wt% at (cryogenic temperature 77 K, 50 bar) and 0.72 wt% at (room temperature 298 K, 100 bar) for the absolute; 4.63 wt% at (77 K, 10 bar) and 0.29 wt% at (298 K, 100 bar) for the excess capacity. Furthermore, Sc-MIL-88A also exhibited the highest volumetric uptake up to 52 g L⁻¹ at 77 K and 7.1 g L⁻¹ at 298 K for the absolute; 46 g L⁻¹ at 77 K and 2.8 g L⁻¹ at 298 K for the excess loading.

中文翻译：

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通过MIL-88A金属-有机骨架中的金属取代增强储氢

具有不饱和铁金属配位点的MIL-88A金属有机骨架已被证明是用于气体存储和捕获的有前途的材料。但是，必须提高MIL-88A的储氢能力，使其在环境条件下满足实际水平。在这项研究中，我们阐明了过渡金属取代对MIL-88A储氢能力的影响。已选择三价过渡金属（包括Sc，Ti，V，Cr，Mn和Ni）替代MIL-88A中的Fe。使用范德华分散校正的密度泛函理论计算，我们探索了M-MIL-88A（M = Sc，Ti，V，Cr，Mn，Ni）中氢分子最有利的吸附构型。我们发现，V-MIL-88A具有最强的结合能17 kJ mol ^-1氢分子在金属部位呈侧向配置。此外，经典的蒙特卡洛模拟结果表明，由于H ₂ @ MIL-88A相互作用的改变，金属取代不仅极大地影响了良好的吸附构型和能量，而且极大地影响了氢的吸收。与其他M-MIL-88A相比，发现Sc-MIL-88A的H ₂吸收量最高。绝对值在（低温温度77 K，50 bar）下为5.13 wt％，在（室温298 K，100 bar）下为0.72 wt％。对于多余的容量，在（77 K，10 bar）下为4.63 wt％，在（298 K，100 bar）下在0.29 wt％。此外，SC-MIL-88A还显示出最高的容积摄取高达52克L- ^-1在77K和7.1克L- ^-1绝对值为298 K；对于^超负荷，在77 K时为46 g L ^-1，在298 K时为2.8 g L ^-1。