Hydrogen storage properties of Mg-Ni-Fe composites prepared by hydriding combustion synthesis and mechanical milling

We reported the structures and superior hydrogen storage properties of the composites Mg ₉₀Ni _10-xFe _x (x = 0, 2, 4, 6 and 8) prepared by the process of HCS + MM, i.e., the hydriding combustion synthesis followed by mechanical milling. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDX) and gas reaction controller (GRC), the crystal structures, surface morphologies and hydriding/dehydriding properties of the composites were studied in detail. The Mg ₉₀Ni _10-xFe _x (x = 2, 4, 6 and 8) composites consist of MgH ₂, Mg, Mg ₂NiH ₄, Mg ₂NiH _0.3 and Fe phases, while Mg ₉₀Ni ₁₀ is composed of MgH ₂, Mg, Mg ₂NiH ₄ and Mg ₂NiH _0.3. It is found that Mg ₉₀Ni ₂Fe ₈ has the best hydriding properties, requiring only 30 s to absorb 97% of its saturated hydrogen capacity of 4.80 wt.% at 373 K. The best dehydriding result is obtained with Mg ₉₀Ni ₈Fe ₂, which desorbs 2.02 and 4.40 wt.% hydrogen at 493 and 523 K, respectively. The microstructures of the composites prepared by HCS + MM have remarkable influences on the enhanced hydriding/dehydriding properties. In addition, the catalytic effects of Mg ₂Ni and Fe phases during hydriding/dehydriding were discussed in this study.