Room Temperature Hydrogen Physisorption on Exposed Metals in A Highly Cross‐Linked Organo‐Iron Complex

Abstract

ambient temperature range have been observed in a number of materials of this class. [ 9,11,12 ] To date, signifi cant hydrogen uptake at room temperature has only been observed in compounds of the latter two classes but none of the physisorption materials has been found to exhibit a hydrogen capacity that meets the gravimetric and volumetric targets set by the U.S. Department of Energy. [ 13 ] We note here that the surface area of class two materials is in general substantially smaller than that of class-one and class-three compounds with metal hydrazide gel materials as a typical example. [ 7,8 ] The highest hydrogen capacity of the class-three materials reported to date is 1.01 wt% at room temperature and 90 atm, in spite of the large surface area up to 5109 m 2 g −1 , likely attributed to the limited access of the active metal sites available to H 2 molecules. [ 14 ] Clearly, an appropriate porosity and abundant adsorption sites are two essential attributes required to induce strong physisorption at a near ambient temperature.In this Communication, we report an attempt to synthesize a complex with a moderate surface area and relatively dense under-coordinated iron metals for room temperature hydrogen storage via physisorption. The under-coordinated iron atoms, which serve as the active sites for hydrogen adsorption, are accommodated in a melamine-terephthaldehyde framework (MTF-Fe). The synthesized complex displays a wide range of nano-pores with a specifi c surface area up to 175 m 2 g −1 ; each iron atom is under-coordinated by formally forming only four bonds with the organic framework and is exposed on the walls of the nano-pores. This architecture facilitates diffusion and adsorption of hydrogen molecules in the network and enables storage to be realized via PSA at a near ambient temperature. Indeed, a measurement of hydrogen uptake yields a gravimetric storage capacity up to 1.7 wt% at 298K and 100 atm, substantially higher than the value for most MOF compounds and high surface area carbon materials and comparable to the hydrogen capacity of the best hydrogen physisorption materials reported to date under similar conditions. [ 5,14,15 ] Melamine-terephthaldehyde based compounds with crosslinked porous organic frameworks were successfully synthesized recently. [ 16,17 ] These materials exhibit high thermal stability, large surface areas and high porosity. Similar to most MOF compounds, the melamine-terephthaldehyde based complexes display virtually no activity toward hydrogen at a near ambient temperature due to lack of active sites. By adopting a similar synthesis protocol, schematically shown in Scheme 1 , but incorporating under-coordinated organo-iron species active to hydrogen molecules in the precursors, a material with a moderate surface area but numerous coordinatively unsaturated iron ions exposed on the walls of a polymeric network was then formed.The development of materials capable of storing hydrogen in high capacity via physical interaction at near ambient temperatures has long been recogni...

Water‐Based Assembly of Polymer–Metal Organic Framework (MOF) Functional Coatings

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Hydrogen Storage in a Crosslinked Phloroglucinol-Terephthalaldehyde Framework with Exposed Iron Sites

“…Notably, the apparatus with an empty sample chamber was thoroughly calibrated prior to the test to rule out a linear increase of uptake upon gas compression. The instrument calibration and the experimental considerations are published elsewhere [11][12][13]15,18] .…”

“…Hydrogen adsorption measurements were performed by following the standard practice guidelines provided by the US Department of Energy to minimize potential errors in the hydrogen uptake measurement [30][31][32] . The instrument calibration and the experimental considerations are published elsewhere [11][12][13]15,18] .…”

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