Effect of graphite (GR) content on microstructure and hydrogen storage properties of nanocrystalline Mg24Y3–Ni–GR composites

Abstract

Ternary Mg24Y3–5 wt.% Ni–x wt.% GR (x = 0–10) composites were prepared by mechanical ball-milling. The phase composition, microstructure and hydrogen storage properties were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Sievert's testing method. Results show that adding an appropriate amount of GR has a beneficial effect on reducing particle size and promoting ball-milling efficiency. Sample with 3 wt.% GR content has a composite structure composed of amorphous and nanocrystalline, as a result, showing an excellent hydrogen absorption kinetics even at 100 °C. Differential scanning calorimetry (DSC) tests were used to evaluate the dehydrogenation performance. The peak temperature was reduced from 325 °C to 295 °C with increasing GR content from 0 to 3 wt.%, which can be attributed to the grain refinement and contact improvement between catalytic Ni and Mg24Y3 alloy particles. However, larger flaky Mg24Y3 alloy particles were observed with a further increase of GR content, which is mainly due to the excessive GR addition reduces ball-milling efficiency. The benefit would be completely lost with the GR adding amount up to 10 wt.%.