Abstract
The porosity and hydrogen storage properties of the dehydrated Prussian blue type solids Ga[Co(CN) 6], Fe 4[Fe(CN) 6] 3, M 2[Fe(CN) 6] (M = Mn, Co, Ni, Cu), and Co 3[Co(CN) 5] 2 are reported and compared to those of M 3[Co(CN) 6] 2 (M = Mn, Fe, Co, Ni, Cu, Zn). Nitrogen sorption measurements suggest partial framework collapse for M 2[Fe(CN) 6] (M = Co, Ni) and Co 3[Co(CN) 5] 2, and complete collapse for Mn 2[Fe(CN) 6]. Hydrogen sorption isotherms measured at 77 K reveal a correlation between uptake capacity and the concentration of framework vacancies, with Langmuir–Freundlich fits predicting saturation values of 1.4 wt.% for Ga[Co(CN) 6], 1.6 wt.% for Fe 4[Fe(CN) 6] 3, 2.1 wt.% for Cu 3[Co(CN) 6] 2, and 2.3 wt.% for Cu 2[Fe(CN) 6]. Enthalpies of H 2 adsorption were calculated from isotherms measured at 77 and 87 K. Importantly, the values obtained for compounds with framework vacancies are not significantly greater than for the fully-occupied framework of Ga[Co(CN) 6] (6.3–6.9 kJ/mol). This suggests that the exposed metal coordination sites in these materials do not dominate the hydrogen binding interaction.
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