Materials capable of cost-effective on-board hydrogen storage and delivery are currently being sought worldwide as a means to facilitate a hydrogen-based energy transition in the transportation sector. Among the solutions proposed, hydrogen storage by physisorption on porous solids constitutes a main avenue of research, and for intelligent design of such materials a detailed knowledge of gas adsorption thermodynamics is of the utmost importance. Analysis of the available data for hydrogen adsorption on alkali and alkaline-earth cation exchanged zeolites clearly shows that standard adsorption enthalpy (D H0) and entropy (D S0) are correlated, in the sense that larger D S0 values correspond to larger D H0 values. It was also shown that, referring to absolute values, the relative rate at which adsorption entropy changes decreases gradually as adsorption enthalpy increases thus resulting in a non-linear correlation between D H0 and D S0. These results are discussed and corresponding implications for hydrogen storage via physisorption are highlighted.

Materials capable of cost-effective on-board hydrogen storage and delivery are currently being sought worldwide as a means to facilitate a hydrogen-based energy transition in the transportation sector. Among the solutions proposed, hydrogen storage by physisorption on porous solids constitutes a main avenue of research, and for intelligent design of such materials a detailed knowledge of gas adsorption thermodynamics is of the utmost importance. Analysis of the available data for hydrogen adsorption on alkali and alkaline-earth cation exchanged zeolites clearly shows that standard adsorption enthalpy (D H0) and entropy (D S0) are correlated, in the sense that larger D S0 values correspond to larger D H0 values. It was also shown that, referring to absolute values, the relative rate at which adsorption entropy changes decreases gradually as adsorption enthalpy increases thus resulting in a non-linear correlation between D H0 and D S0. These results are discussed and corresponding implications for hydrogen storage via physisorption are highlighted.