Core–shell Prussian blue analogue molecular magnet Mn_1.5[Cr(CN)₆]·mH₂O@Ni_1.5[Cr(CN)₆]·nH₂O for hydrogen storage

Abstract

Core–shell Prussian blue analogue molecular magnet Mn_1.5[Cr(CN)₆]·mH₂O@Ni_1.5[Cr(CN)₆]·nH₂O has been synthesized using a core of Mn_1.5[Cr(CN)₆]·7.5H₂O, surrounded by a shell of Ni_1.5[Cr(CN)₆]·7.5H₂O compound. A transmission electron microscopy (TEM) study confirms the core–shell nature of the nanoparticles with an average size of ∼25 nm. The core–shell nanoparticles are investigated by using x–ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and elemental mapping, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and infrared (IR) spectroscopy. The Rietveld refinement of the XRD pattern reveals that the core–shell compound has a face–centered cubic crystal structure with space group Fm3m. The observation of characteristic absorption bands in the range of 2000–2300 cm^–1 in IR spectra corresponds to the CN stretching frequency of Mn^II/Ni^II–N≡C–Cr^III sequence, confirming the formation of Prussian blue analogues. Hydrogen absorption isotherm measurements have been used to investigate the kinetics of molecular hydrogen adsorption into core–shell compounds of the Prussian blue analogue at low temperature conditions. Interestingly, the core–shell compound shows an enhancement in the hydrogen capacity (2.0 wt % at 123 K) as compared to bare–core and bare–shell compounds. The hydrogen adsorption capacity has been correlated with the specific surface area and TGA analysis of the core–shell compound. To the best of our knowledge, this is the first report on the hydrogen storage properties of core–shell Prussian blue analogue molecular magnet that could be useful for hydrogen storage applications.