The porosity and H storage properties of the dehydrated Prussian blue type solids Ga[Co(CN)6], Fe4[Fe(CN)6]3, M2[Fe(CN)6] (M = Mn, Co, Ni, Cu), and Co3[Co(CN)5]2 were reported and compared to those of M3[Co(CN)6]2 (M = Mn, Fe, Co, Ni, Cu, Zn). Nitrogen sorption measurements suggest partial framework collapse for M2[Fe(CN)6] (M = Co, Ni) and Co3[Co(CN)5]2, and complete collapse for Mn2[Fe(CN)6]. Hydrogen sorption isotherms measured at 77K reveal a correlation between uptake capacity and the concentration of framework vacancies, with Langmuir–Freundlich fits predicting saturation values of 1.4wt% for Ga[Co(CN)6], 1.6wt% for Fe4[Fe(CN)6]3, 2.1wt% for Cu3[Co(CN)6]2, and 2.3wt% for Cu2[Fe(CN)6]. Enthalpies of H2 adsorption were calculated from isotherms measured at 77 and 87K. Importantly, the values obtained for compounds with framework vacancies were not significantly greater than for the fully-occupied framework of Ga[Co(CN)6] (6.3 to 6.9kJ/mol). This suggests that the exposed metal coordination sites in these materials did not dominate the H binding interaction.

The Role of Vacancies in the Hydrogen Storage Properties of Prussian Blue Analogues. S.S.Kaye, J.R.Long: Catalysis Today, 2007, 120[3-4], 311-6