Hydrogen storage properties of compacts of melt-spun Mg90Ni10 flakes and expanded natural graphite

In recent years, melt-spun magnesium alloys have attracted a lot of attention due to their excellent (de-)hydrogenation characteristics resulting from their nanoscale crystal structure and the homogeneous distribution of minor catalyst phases. Besides reaction kinetics, the heat conductivity of the storage material is important to transfer the reaction enthalpies in a controlled manner. Due to the inferior heat conduction properties of magnesium hydride, composites containing melt-spun Mg90Ni10 flakes and expanded natural graphite (ENG) up to 25.5 wt.% have been examined. Mixtures of those starting materials were compacted to cylindrical pellets using compaction pressures up to 600 MPa. Investigations of thermal conductivities in radial and axial directions, microstructure and phase fractions were carried out upon all sets of specimens. The heat transfer characteristics were tuned in a wide range from 1 up to 47 W m−1 K−1. Furthermore, cyclic (de-)hydrogenation was carried out upon the compacts showing a hydrogen uptake of up to 4 wt.%-H2 within 10 min. During the hydrogen loading process, the Mg90Ni10–ENG pellets remained mechanically stable.

Research highlights▶ Pelletized composites of melt-spun Mg90Ni10 flakes and expanded natural graphite show strong anisotropy in thermal conductivity. ▶ Tuning of thermal conductivity in a wide range is demonstrated: 1–47 W m−1 K−1. ▶ Pellets show a hydrogen uptake rate of up to 4 wt.%-H2 within 10 min. ▶ Pelletized composites remain mechanically stable during cyclic hydrogenation/dehydrogenation.