No abstract

Three structurally diverse polymers of intrinsic microporosity reversibly adsorb significant quantities of hydrogen (1.4–1.7 % by mass at 77 K) and represent the first examples of a new type of purely organic hydrogen storage material, which can be tailored to meet the specific requirements of hydrogen physisorption.

A novel triptycene-based polymer of intrinsic microporosity (Trip-PIM) displays enhanced surface area (1065 m2 g(-1)) and reversibly adsorbs 1.65% hydrogen by mass at 1 bar/77 K and 2.71% at 10 bar/77 K.

We report the synthesis and properties of network polymers of intrinsic microporosity (network−PIMs) derived from triptycene monomers that possess alkyl groups attached to their bridgehead positions. Gas adsorption can be controlled by the length and branching of the alkyl chains so that the apparent BET surface area of the materials can be tuned within the range 618−1760 m2 g−1. Shorter (e.g., methyl) or branched (e.g., isopropyl) alkyl chains provide the materials of greatest microporosity, whereas longer alkyl chains appear to block the microporosity created by the rigid organic framework. The enhanced microporosity, in comparison to other PIMs, originates from the macromolecular shape of the framework, as dictated by the triptycene units, which helps to reduce intermolecular contact between the extended planar struts of the rigid framework and thus reduces the efficiency of packing within the solid. The hydrogen adsorption capacities of the triptycene-based PIMs with either methyl or isopropyl substituents are among the highest for purely organic materials at low or moderate presures (1.83% by mass at 1 bar/77K; 3.4% by mass at 18 bar/77 K). The impressive hydrogen adsorption capacity of these materials is related to a high concentration of subnanometre micropores, as verified by Horvath−Kawazoe analysis of low-pressure nitrogen adsorption data.

No abstract

We have investigated the decomposition path and reversibility of Ca(BH4)2 and Ca(BH4)2 + MgH2 composite using X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and Raman spectroscopy. Formation of CaB6 during dehydrogenation of both systems was confirmed for the first time. CaB6 appears as broad peaks in X-ray diffraction data, but Raman spectroscopy unambiguously captures the existence of CaB6. Reversibility of catalyzed Ca(BH4)2 was previously reported, and here we demonstrate reversibility of Ca(BH4)2 + MgH2 composite. Dehydrogenated product of Ca(BH4)2 + MgH2 is composed of CaH2, CaB6, and Mg. About 60% reversibility was achieved after rehydrogenation for 24 h under 90 bar of hydrogen pressure at 350 °C even without the help of catalysts, which makes a good contrast with the case of pure Ca(BH4)2 where almost negligible rehydrogenation occurs under the same conditions. To understand the difference, the role of Mg in rehydrogenation is worth further investigation. Formation of CaB6 seems critical in the reversibility of Ca(BH4)2 containing systems; the case of other borohydrides is compared.

No abstract

The challenge of storing hydrogen at high volumetric and gravimetric density for automotive applications has prompted investigations into the potential of cryo-adsorption on the internal surface area of microporous organic polymers. A range of Polymers of Intrinsic Microporosity (PIMs) has been studied, the best PIM to date (a network-PIM incorporating a triptycene subunit) taking up 2.7% H(2) by mass at 10 bar/77 K. HyperCrosslinked Polymers (HCPs) also show promising performance as H(2) storage materials, particularly at pressures >10 bar. The N(2) and H(2) adsorption behaviour at 77 K of six PIMs and a HCP are compared. Surface areas based on Langmuir plots of H(2) adsorption at high pressure are shown to provide a useful guide to hydrogen capacity, but Langmuir plots based on low pressure data underestimate the potential H(2) uptake. The micropore distribution influences the form of the H(2) isotherm, a higher concentration of ultramicropores (pore size <0.7 nm) being associated with enhanced low pressure adsorption.