Neutron Diffraction and Neutron Vibrational Spectroscopy Studies of Hydrogen Adsorption in the Prussian Blue Analogue Cu₃[Co(CN)₆]₂

The adsorption of molecular hydrogen in the Prussian blue analogue Cu 3 [Co(CN) 6 ] 2 was investigated using high-resolution neutron powder diffraction and neutron vibrational spectroscopy. Rietveld structural refinement of the neutron data for hydrogen loadings of 1, 2, and ∼2.3 H 2 /Cu showed that the hydrogen was absorbed at two sites within the structure. The most prominent adsorption site, located at the ( 1 / 4, 1 / 4, 1 / 4 ) crystallographic site, was an interstitial location within the structure. The second adsorption site was associated with exposed Cu 2+ ion coordination sites that result from the presence of [Co(CN) 6 ] 3 - vacancies within the structure of the material. The rotational−vibrational density of states of the adsorbed hydrogen was probed using neutron vibrational spectroscopy and showed a range of local binding potentials for the adsorbed hydrogen.