A comparative investigation of H2 adsorption strength in Cd- and Zn-based metal organic framework-5

Hydrogen binding energies for the primary and secondary adsorption sites in the Cd- and Zn-based metal organic framework-5 (MOF-5) were studied using density functional theory. Out of the three exchange-correlation functionals employed in our study, we find that the local density approximation yields a qualitatively correct description of the interaction strengths of H-2 in MOF-5 systems. The H-2 adsorption energies for all trapping sites in Zn- and Cd-based MOF-5 are seen to be of the same order of magnitude but with a generally stronger binding in Cd- based MOF-5 as compared to Zn- based MOF-5. In particular, the H-2 binding energy at the secondary adsorption sites in Cd- based MOF-5 is increased by around 25% compared to Zn-based MOF-5. This result suggests that Cd- based MOF-5 would be better suited to store hydrogen at higher temperatures than Zn-based MOF-5. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2997377].