In situ temperature field distribution via LiH and polyethylene glycol additives to enhance the hydrolysis performances of magnesium-calcium hydrides

Hydrogen generation by hydrolysis of magnesium-based materials offers significant advantages by integrating three keys aspects: involving hydrogen generation, storage and transportation. Our previous work developed Mg-20 wt% Ca hydride (MCH), which improved the hydrolysis performances of magnesium-based materials. However, the formation of Mg(OH)₂ hinders further hydrolysis progression, resulting in slow kinetics and a relatively low hydrogen conversion rate in practical applications. To address these challenges, we prepared novel MCH-xLiH (x=0, 5, 10, 20 wt%) composites. Results showed that the in situ temperature field generated by LiH hydrolysis facilitates the hydrolysis kinetics of MCH, and the highly soluble LiOH destroys the Mg(OH)₂ passivation layer to provide more water molecular channels. The hydrogen yield of MCH-5LiH in deionized water at 25 ℃ reaches 1015.9 mL g^-1, which is 1.85 times higher than that of MCH. The hydrolysis activation energy for MCH-5LiH decreases from 15.40 kJ mol^-1 (for MCH) down to 11.82 kJ mol^-1. Further, considering the safety of practical applications, MCH-5LiH was coated with polyethylene glycol 1000 (referred to as PEG) to regulate the distribution of the in situ temperature field during the reaction. The sluggish dissolution of PEG prolonged the reaction time, delayed the heat generation rate, and kept the temperature field within the safe range for a longer time. The peak reaction temperature decreases from 329.9 ℃ for MCH-5LiH to 90.2 ℃ for (MCH-5LiH)-20PEG. Coating MCH-5LiH with PEG not only improves the safety during application but also ensures the hydrolysis conversion rate of the materials. This work provided a promising reference for the large-scale application of magnesium-calcium-based hydrolysis materials.