Catalytic effect of 3d transition metals on hydrogen storage properties in mechanically milled graphite

Abstract

In this paper, we examined the catalytic effect of 3d transition metals on hydrogen storage properties in nanostructural graphite prepared by ball milling under hydrogen atmosphere. The Fe-doped nanostructured graphite shows the most marked hydrogen storage properties among the Fe-, Co-, Ni- and Cu-catalyzed graphite systems. The absorbed hydrogen concentration reaches up to ∼4 wt% by mechanically milling for 32 h (∼7 wt% for 80 h), and two peaks of hydrogen (mass number=2) around 730 and 1050 K were observed in the thermal desorption mass spectra (TDS). The starting temperature for hydrogen desorption was ∼600 K. On the other hand, the Co-doped graphite indicates that absorbed hydrogen concentrations reaches up to ∼2 wt% by mechanically milling for 32 h. The TDS spectrum showed only a broad peak around 1100 K, but the starting point for hydrogen desorption lowered down to ∼500 K. The Ni- and Cu-doped graphites did not show any significant improvement for hydrogen storage. These results suggest that the catalytic effect on hydrogen storage properties strongly depends on the affinity of graphite and doped metals.