Exploring the structural, hydrogen storage capacity, electronic and optical properties of H-rich AlHx(x=4, 5 and 6) hydrogen storage materials: A first-principles study

Although Al-H hydrides are promising hydrogen storage materials due to the high hydrogen storage capacity and low density, the structural stability, electronic and optical properties of H-rich region AlHx x are entirely unknown. To explore the hydrogen storage material with high hydrogen storage capacity, here, we apply the first-principle method to study the structural stability, hydrogen storage capacity, electronic and optical properties of three AlHx x (x = 4, 5 and 6) hydrides. The calculated results show that three AlHx x hydrides are thermodynamic stability due to the negative formation enthalpy. In particular, it is found that the calculated hydrogen storage capacity (Cwt.%) wt .%) is 11.44 wt% for AlH4, 4 , 13.52 wt% for AlH5 5 and 15.39 wt% for AlH6, 6 , respectively. Compared to MgH2 2 (7.66 wt%), the hydrogen storage capacity of AlH4, 4 , AlH5 5 and AlH6 6 increases by about 49.3%, 76.5% and 100.9%. Naturally, the [AlH3] 3 ] group and [AlH5] 5 ] group in AlH5, 5 , the [AlH6] 6 ] group in AlH4 4 and AlH6 6 are beneficial to store a lot of hydrogen. In addition, the calculated band gap of AlH4, 4 , AlH5 5 and AlH6 6 is 3.08 eV, 3.11 eV and 4.27 eV, respectively. The semiconductor properties of three AlHx x hydride is demonstrated by the dielectric functional. Finally, it is found that three AlHx x hydrides show ultraviolet properties.