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

The role of additional ternary alloying elements on the performance of stationary TiFe-based hydrogen storage alloys was investigated based on first-principles density functional theory calculations. As a basic step for examinations, the site preference of each alloying element in the stoichiometric and non-stoichiometric B2 TiFe compounds was clarified considering possible anti-site defects. Based on the revealed site preference, the effect of various possible ternary elements on the hydrogen storage was examined by focusing on the formation enthalpies of TiFeH and TiFeH2 hydrides, which were closely related to the change in the location of plateaus in the pressure−composition−temperature curve. Several physical properties such as the volume expansion due to hydride formation were also examined to provide additional criteria for selecting optimum alloying conditions in future alloying design processes. Candidate alloying elements that maximize the grain boundary embrittlement due to the solute segregation were proposed for the enhanced initial activation of TiFe-based hydrogen storage alloys.