Hydrogenation Study of NaF/NaH/MgB2 Reactive Hydride Composites


The hydrogenation of NaF/9NaH + 5MgB2 and NaF/2NaH + 1.5MgB2 reactive hydride composites (RHC) was studied by volumetric titration (kinetics and PCI curves), in situ synchrotron radiation powder X-ray diffraction (SR-PXD), high-pressure differential scanning calorimetry (HP-DSC), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM). A hydrogen uptake between 4.1 and 4.8 wt % was observed when the H2 pressure was in the range between 25 and 50 bar, and the temperature was kept constant at 325 °C. PCI curves indicate a hydrogenation equilibrium pressure of 2 and 8 bar at 325 °C for NaF/9NaH + 5MgB2 and NaF/2NaH + 1.5MgB2, respectively. Synchrotron radiation powder X-ray diffraction revealed the formation of solid solutions of NaF–NaH after milling and a change in the reaction pathway compared to a reported nondoped 2NaH + MgB2 reactive hydride composite. Formation of the stable side-product NaMgH2F was found as a drawback for hydrogen storage capacity and reversibility. FT-IR indicates no hydrogen to fluorine substitution in the NaBH4 product.
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