Hydrogen Storage in Prussian Blue Analogues: H2Interaction with the Metal Found at the Cavity Surface

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In open framework Prussian blue analogues, all of the metal atoms linked at the N end of the CN groups are found at the surface of the cavities with an unsaturated coordination environment. These metal sites are available for a specific interaction with guest species. To shed light on the H 2 interaction with these metal sites, H 2 adsorption isotherms in Ni 3− x Mn x [Co(CN) 6 ] 2, Ni 3− x Co x [Co(CN) 6 ] 2, Ni 3− x Cd x [Co(CN) 6 ] 2, and Co 3− x Mn x [Co(CN) 6 ] 2 were recorded and evaluated. According to the obtained data for the adsorption heat values, the strongest H 2 −metal interaction was found for Ni. The same evidence is obtained from the fitting of the isotherms using the osmotic model, where the value for the osmotic parameter ( g ) senses the strength for the guest−host interaction. The probable origin of that stronger interaction for the Ni atom is discussed. The information derived from these mixed series was complemented with an analogue study for T 3 [Co(CN) 6 ] 2 and T 3 [Ir(CN) 6 ] 2, with T = Mn, Co, Ni, Zn, Cu, and Cd. The strength for the guest−host interaction in these two simple series follows the order: Ni > Cu > Co ∼ Cd > Mn ∼ Zn. For the series T 3 [Co(CN) 6 ] 2, H 2 adsorption isotherms up to 7600 Torr were recorded, confirming that the strongest H 2 −metal interaction corresponds to Ni and Cu. The samples to be studied were characterized from energy-dispersed spectroscopy, X-ray diffraction, infrared, and CO 2 adsorption data.