Jaramillo David E, Jiang Henry Z H, Evans Hayden A, Chakraborty Romit, Furukawa Hiroyasu, Brown Craig M, Head-Gordon Martin, Long Jeffrey R
Department of Chemistry, University of California, Berkeley, California 94720, United States.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
J Am Chem Soc. 2021 Apr 28;143(16):6248-6256. doi: 10.1021/jacs.1c01883. Epub 2021 Apr 14.
The widespread implementation of H as a fuel is currently hindered by the high pressures or cryogenic temperatures required to achieve reasonable storage densities. In contrast, the realization of materials that strongly and reversibly adsorb hydrogen at ambient temperatures and moderate pressures could transform the transportation sector and expand adoption of fuel cells in other applications. To date, however, no adsorbent has been identified that exhibits a binding enthalpy within the optimal range of -15 to -25 kJ/mol for ambient-temperature hydrogen storage. Here, we report the hydrogen adsorption properties of the metal-organic framework (MOF) VCl(btdd) (Hbtdd, bis(1-1,2,3-triazolo[4,5-],[4',5'-])dibenzo[1,4]dioxin), which features exposed vanadium(II) sites capable of backbonding with weak π acids. Significantly, gas adsorption data reveal that this material binds H with an enthalpy of -21 kJ/mol. This binding energy enables usable hydrogen capacities that exceed that of compressed storage under the same operating conditions. The Kubas-type vanadium(II)-dihydrogen complexation is characterized by a combination of techniques. From powder neutron diffraction data, a V-D(centroid) distance of 1.966(8) Å is obtained, the shortest yet reported for a MOF. Using infrared spectroscopy, the H-H stretch was identified, and it displays a red shift of 242 cm. Electronic structure calculations show that a main contribution to bonding stems from the interaction between the vanadium and H σ* orbital. Ultimately, the pursuit of MOFs containing high densities of weakly π-basic metal sites may enable storage capacities under ambient conditions that far surpass those accessible with compressed gas storage.
将氢气用作燃料的广泛应用目前受到实现合理存储密度所需的高压或低温的阻碍。相比之下，若能实现可在环境温度和中等压力下强烈且可逆地吸附氢气的材料，则可变革交通运输领域，并扩大燃料电池在其他应用中的采用。然而，迄今为止，尚未发现一种吸附剂在环境温度储氢的最佳焓值范围（-15至-25 kJ/mol）内表现出结合焓。在此，我们报告金属有机框架（MOF）VCl(btdd)（Hbtdd，双（1-1,2,3-三唑并[4,5-],[4',5'-]）二苯并[1,4]二恶英）的氢吸附特性，其具有能够与弱π酸进行反馈键合的暴露钒（II）位点。值得注意的是，气体吸附数据表明该材料以-21 kJ/mol的焓结合氢气。这种结合能使得在相同操作条件下的可用氢容量超过压缩存储的氢容量。通过多种技术对库巴斯型钒（II）-二氢络合物进行了表征。从粉末中子衍射数据中，获得了1.966(8) Å的V-D（质心）距离，这是MOF报道中最短的。利用红外光谱法，识别出了H-H伸缩振动，其显示出242 cm的红移。电子结构计算表明，键合的主要贡献源于钒与H σ*轨道之间的相互作用。最终，追求含有高密度弱π碱性金属位点的MOF可能使环境条件下的存储容量远远超过压缩气体存储的容量。
