Hydrogen storage properties of ball-milled graphite with 0.5wt% Fe

Ball-milled hydrogenated graphite-iron materials have attracted interest as possible hydrogen storage media because of theoretically estimated hydrogen capacities of about 10wt%. However, such a value needs to be experimentally verified. In this work, graphite-0.5wt% Fe was milled under 3bar hydrogen in a tungsten carbide milling pot. The effect of iron on the microstructure and hydrogen storage properties of milled graphite was investigated by thermal gravimetric analysis-mass spectrometry, X-ray diffraction, and transmission electron microscopy. When a 10-hour milled graphite with 0.5wt% Fe sample was heated under argon to 990°C, 9.6wt% of hydrogen was released, which is almost double than that for a graphite sample with no iron (5.5wt% hydrogen). The addition of iron also was found to reduce the onset temperature of hydrogen desorption by 50 to 350°C. However, for a longer milling time of 40hours, the amount of hydrogen desorbed for graphite-0.5wt% Fe decreased, and methane also was detected. The results suggest that iron carbide produced during milling plays a catalytic role, increasing the hydrogen storage capacity and lowering the onset temperature of hydrogen desorption.