Density functional theory study on the role of ternary alloying elements in TiMn2-based hydrogen storage alloys

First-principles density functional theory (DFT) calculations are performed to elucidate the role of additional alloying elements on the performance of TiMn2-based hydrogen storage alloys. In particular, the site preference of each alloying element in stoichiometric and off-stoichiometric Ti-rich and Mn-rich C14 Laves-type TiMn2-based compounds was clarified by considering possible antisite defects. Based on the revealed site preference, the effect of the alloying elements on the reaction enthalpy of the TiMn2H3 hydride is examined to reveal the qualitative trend regarding the location of the hydrogen plateau pressures in the pressure–composition–temperature (PCT) curve, and the predictions are validated by comparing them to reported experimental trends. To provide further criteria for alloy design, the effects of solute elements on the dilatation of hydrogen storage alloys caused by the hydrogenation reaction, which is a crucial factor considered for the practical usage of hydrogen storage alloys, were calculated. The proposed method and obtained prediction results serve as a theoretical basis for the future alloying design process of TiMn2-based hydrogen storage alloys with the desired properties for target applications.