Hydrogen generation behaviors from hydrolysis of cold-welding free magnesium-calcium hydride-expanded graphite composites

Hydrolysis of magnesium-based materials is a promising hydrogen source for fuel cells. Our previous work (Liu et al. 2015) proposed the 30 wt% calcium-magnesium alloy hydrides (MCH) with superior hydrolysis performance than magnesium and magnesium hydride. But the easily-happened cold-welding reduces the pulverization efficiency. Additionally, the hydrolysis conversion rate at room temperature remains low. In current work, we have explored the novel composites including MCH and 0-20 wt% expanded graphite (EG) to examine the impact and underlying mechanisms of EG as additive in mitigating cold-welding and enhancing hydrolysis. The results suggest that EG coats on the material surface as a dispersant to prevent cold-welding, optimize ball milling efficiency and reduce particle size, further facilitating hydrogenation and hydrolysis. In deionized water, MCH with 10 wt% EG (MCH-10EG) displays the best hydrolysis performance, with a low activation energy of 11.26 kJ mol-1 and a complete conversion within 8 min at 55 degrees C. Moreover, at room temperature, combined with the corrosion effects of Cl- and H+ to break the formed magnesium hydroxide passivation layer, MCH-10EG achieves a complete conversion within only 5 min in 0.3 mol L-1 aluminum chloride solution. This work may significantly advance the large-scale production and practical application of magnesium-calcium-based hydrolysis materials as hydrogen source.