Mechanochemical modification of LiAlH4 with Fe2O3 - A combined DFT and experimental study

Abstract

LiAlH4 is a promising material for hydrogen storage, having the theoretical gravimetric density of 10.6 wt% H2. In order to decrease the temperature where hydrogen is released, we investigated the catalytic influence of Fe2O3 on LiAlH4 dehydrogenation, as a model case for understanding the effects transition oxide additives have in the catalysis process. Quick mechanochemical synthesis of LiAlH4 + 5 wt% Fe2O3 led to the significant decrease of the hydrogen desorption temperature, and desorption of over 7 wt%H2 in the temperature range 143–154 °C. Density functional theory (DFT)-based calculations with Tran-Blaha modified Becke-Johnson functional (TBmBJ) address the electronic structure of LiAlH4 and Li3AlH6. 57Fe Mössbauer study shows the change in the oxidational state of iron during hydrogen desorption, while the 1H NMR study reveals the presence of paramagnetic species that affect relaxation. The electron transfer from hydrides is discussed as the proposed mechanism of destabilization of LiAlH4 + 5 wt% Fe2O3. © 2021 Hydrogen Energy Publications LLC