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 AlH 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 AlH x (x = 4, 5 and 6) hydrides. The calculated results show that three AlH x hydrides are thermodynamic stability due to the negative formation enthalpy. In particular, it is found that the calculated hydrogen storage capacity (C wt .%) is 11.44 wt% for AlH 4 , 13.52 wt% for AlH 5 and 15.39 wt% for AlH 6 , respectively. Compared to MgH 2 (7.66 wt%), the hydrogen storage capacity of AlH 4 , AlH 5 and AlH 6 increases by about 49.3%, 76.5% and 100.9%. Naturally, the [AlH 3 ] group and [AlH 5 ] group in AlH 5 , the [AlH 6 ] group in AlH 4 and AlH 6 are beneficial to store a lot of hydrogen. In addition, the calculated band gap of AlH 4 , AlH 5 and AlH 6 is 3.08 eV, 3.11 eV and 4.27 eV, respectively. The semiconductor properties of three AlH x hydride is demonstrated by the dielectric functional. Finally, it is found that three AlH x hydrides show ultraviolet properties. • Three H-rich region AlH x dihydrides are thermodynamic stability. • The hydrogen storage capacity(C wt .%) of AlH 4 , AlH 5 and AlH 6 is 11.44 wt%, 13.52 wt% and 15.39 wt%. • Compared to MgH 2 , the C wt .% of AlH 4 , AlH 5 and AlH 6 increases by about 49.3%, 76.5% and 100.9%. • The higher hydrogen storage capacity of AlH x relies on the product of [AlH 4 ], [AlH 5 ] and [AlH 6 ] group. • Three AlH x dihydrides exhibit semiconductor properties.