Metal–organic frameworks (MOFs) have become an important focus for the safe and economically applicable storage of hydrogen as a clean fuel. The adsorption enthalpy of molecular hydrogen on MOFs is often used as a measure of potential H2 uptake, but the thermodynamics are not ruled by ΔH0 alone: entropy must also be considered.
Carlos Otero Areán and co-workers at the University of the Balearic Islands, Palma de Mallorca, have determined not only the adsorption energy but also the corresponding entropy term from variable-temperature infrared spectroscopic studies on MOFs with open metal (CrIII) cations.
In light of their results, they argue that the optimum value of ΔH0 for storage/delivery cycles at ambient temperature (in the pressure range 30 to 1.5 bar) is likely to fall in the range –22 to –25 kJmol–1, rather than the often quoted value of –15.1 kJmol–1. As current MOFs have ΔH0 values in the range –9 to –13 kJmol–1, significant improvements still need to be made.
- Enthalpy–Entropy Correlation for Hydrogen Adsorption on MOFs: Variable-Temperature FTIR Study of Hydrogen Adsorption on MIL-100(Cr) and MIL-101(Cr)
Gemma Turnes Palomino, Carlos Palomino Cabello, Carlos Otero Areán,
Eur. J. Inorg. Chem. 2011.