Hydrolysis Kinetics of LiAlH4 at Subzero Temperatures

Abstract

Hydrolysis of LiAlH4 is a promising path to supply hydrogen at low temperatures due to its high hydrogen storage capacity, where an anti-icing aqueous solution is necessary. However, no hydrolysis kinetics of LiAlH4 with an anti-icing aqueous solution has been reported due to its complexity. Herein, an optimized anti-icing aqueous solution with 27.1 wt% KOH and 30.0% ethylene glycol has been found to obtain full and controllable hydrolysis kinetics of LiAlH4 at −40 to 0 °C. The effects of compactness, mass, and temperature on the hydrolysis of LiAlH4 have been investigated. The LiAlH4 tablet with compactness of 92.7% was demonstrated to obtain a wide constant reaction region (>95%) and be suitable for the hydrolysis reactions. The hydrogen release rates at constant reaction regions were found to follow a linear relationship with the 0.42 power of the mass of a compacted LiAlH4 tablet. A strong temperature-dependent hydrolysis was observed, where the activation energy was deduced from experimental data to be 6.83 ± 0.34 kJ·mol–1. The hydrolysis products of LiAlH4 with the adopted anti-icing aqueous solution after washing with deionized water were found to be the same as those directly with water, indicating no consumption of KOH and ethylene glycol in the reactions. The hydrolysis reaction of LiAlH4 with the adopted solution at −40 to 0 °C has been demonstrated to follow the shrinking core model controlled by liquid film diffusion.