Screening New families of Metal Organic Frameworks for Hydrogen Storage

人类现在已经意识到，它对石油的依赖不可能永远持续下去。人们正在疯狂地寻找可行的替代燃料，特别是在汽车工业中使用。氢是一个很有希望的候选能源，因为它可以从各种来源中产生。作为一种清洁的燃烧替代品，氢气有可能将我们的二氧化碳排放量大幅减少到2007年白皮书中建议的水平(到2050年减少60%)，然而，为了实用，任何新燃料都需要安全和紧凑。由于氢在环境温度下是一种气体，它需要在很高的压力下压缩或冷却到很低的温度，才能提供足够的车辆运行所需的供应。无论是高压还是低温都是不可接受的，尤其是出于安全考虑。为了避免这些问题，人们研究了化学储存的方法。目前正在研究的领跑者是微孔材料，它依赖于高比表面积和强大的氢结合亲和力。大规模合成和化学柔性是另一个重要的考虑因素，这使得基于有机间隔物分子连接的金属离子的配位网络进入了橱窗。这些金属有机骨架(MOF)最近显示出潜在的吸氢潜力，基于锌簇合物/羧酸盐连接物的系统在低温下表现出吸氢值，接近美国能源部2010年设定的车载储氢目标。这里的目的是评估一类有前途的新的金属有机骨架，其结构基于通过二酚类间隔物连接的锌(或铝)簇合物。这些体系具有吸氢所需的所有属性，可以在多克规模上制备，并且很容易进行化学修饰，包括在其他体系中显示有利于吸氢的碱金属离子的加入。我们系统中的锌(和铝)团簇也具有侵入性和潜在的有用构象，这些构象创建了非常适合小分子捕获的内部口袋。

Mankind has now realised that its dependance on oil cannot last forever. Viable alternative fuels are frantically being sought, particularly for use in the automobile industry. Hydrogen is emerging as a promising candidate, as it can be generated from a variety of sources. As a clean burning substitute, hydrogen has the potential to dramatically cut our carbon dioxide emissions to the levels suggested in the 2007 White paper (60 % reduction by 2050), however to be practical any new fuel needs to be safe and compact. As hydrogen is a gas at ambient temperatures, it would need to be compressed under very high pressures or cooled to very low temperatures to provide sufficient supplies necessary for the running of vehicles. Neither high pressures nor low temperatures are acceptible, not least on safety grounds. In an attempt to circumvent these problems, methods of chemical storage are been investigated. Amongst the front runners currently under investigation are microporous materials, which relie on high surface area and strong hydrogen binding affinity. Large scale syntheses and chemical flexibility are other important considerations, which put coordination networks based on metal ions linked by organic spacer molecules in the shop window. These metal-organic frameworks (MOFs) have recently shown potential for hydrogen uptake with systems based on zinc clusters/carboxylate linkers exhibiting hydrogen absorption values, albeit at low temperatures, approaching the 2010 targets set by the US Department of Energy for on-board hydrogen storage.It is the intention here to evaluate a promising new familiy of MOFs, the structures of which are based on zinc (or aluminium) clusters linked by diphenolate spacers. These systems possess all the attributes necessary for hydrogen absorption, can be prepared on multi-gramme scale and are readily amenable to chemical modification, including the incorporation of alkali-metal ions shown in other systems to be beneficial to hydrogen uptake. The zinc (and aluminium) clusters in our systems also possess intruiging and potentially useful conformations, which create internal pockets that are well suited to small molecule capture.