Thermodynamics of Hydrogen Adsorption on Metal‐Organic Frameworks

Abstract

Abstract Interaction between adsorbed hydrogen and the coordinatively unsaturated Mg 2+ and Co 2+ cationic centres in Mg‐MOF‐74 and Co‐MOF‐74, respectively, was studied by means of variable‐temperature infrared (VTIR) spectroscopy. Perturbation of the H 2 molecule by the cationic adsorbing centre renders the HH stretching mode IR‐active at 4088 and 4043 cm −1 for Mg‐MOF‐74 and Co‐MOF‐74, respectively. Simultaneous measurement of integrated IR absorbance and hydrogen equilibrium pressure for spectra taken over the temperature range of 79–95 K allowed standard adsorption enthalpy and entropy to be determined. Mg‐MOF‐74 showed Δ H 0 =−9.4 kJ mol −1 and Δ S 0 =−120 J mol −1 K −1 , whereas for Co‐MOF‐74 the corresponding values of Δ H 0 =−11.2 kJ mol −1 and Δ S 0 =−130 J mol −1 K −1 were obtained. The observed positive correlation between standard adsorption enthalpy and entropy is discussed in the broader context of corresponding data for hydrogen adsorption on cation‐exchanged zeolites, with a focus on the resulting implications for hydrogen storage and delivering.