Implications of structural differences between Cu-BTC and Fe-BTC on their hydrogen storage capacity

Hydrogen is an attractive energy vector because it is free of carbon and at the same time contains a high energy density. The main challenge for hydrogen as fuel for massive applications is its storage at high density under technologically viable conditions. In that sense, its physical adsorption in porous solid continues being an option under study. Copper benzene-1,3,5-tricarboxilate (Cu-BTC) is one of the most widely studied metal-organic framework (MOF)-based porous solids, including its potential application for hydrogen storage. Its iron analogue, Fe-BTC has received relatively minor attention probably because it is obtained as a material of low crystallinity and this is a handicap to understand the involved adsorption interactions. In this contribution, we are reporting the implications of their structural differences on the hydrogen storage capacity, with emphasis in the probable guest-host interactions that determine the adsorption process and considering the structural features of them. The samples to be study were prepared using a solvothermal route and then characterized from infrared (IR), Mössbauer, and X-ray photoelectron (XPS) spectroscopies, powder X-ray diffraction (XRD) patterns, thermogravimetric (TG) curves and adsorption data. Both, the H₂ adsorption isotherms and the corresponding adsorption heats show significant differences for the two materials, which are explained according to their structural differences.