Effect of carbon from anthracite coal on decomposition kinetics of magnesium hydride

• Carbon from anthracite coal improved the decomposition kinetics of MgH2.
• Nucleation of new phase started at the grain boundaries of MgH2 and carbon.
• MgH2–Mg interface velocity was rate-limiting step of MgH2 decomposition.

Ball milling of magnesium under hydrogen atmosphere was applied to synthesize MgH2 with carbon from anthracite coal as milling aid. The morphology, crystal structure, and isothermal/non-isothermal hydrogen desorption of the materials were investigated. The TEM observation showed that the particle size of the as-milled material was about 100–150 nm, and the MgH2 particles presented a hexagon-like shape. The XRD analysis showed that the crystallite size of MgH2 increased from 19.4 nm to 52.4 nm after 5 cycles of hydrogen storage, and the DSC, TEM and HRTEM analysis confirmed the growth of crystallite. The FT-IR analysis showed that the carbon could store hydrogen by forming CH bonds and the hydrogen desorption from carbon was easier than that from MgH2. The carbon dispersed the magnesium particles to prevent them from aggregating during milling and improved the decomposition kinetics of MgH2. The formation of nucleation site at MgH2–carbon boundaries was easier than that in MgH2 bulk. The contracting volume model of three-dimensional growth with constant interface velocity (CV 3D civ) described the decomposition kinetics best, and the rate-limiting step was the MgH2–Mg interface velocity along crystal grain boundaries.