Effect of Fe substitution by Mn and Cr on first hydrogenation kinetics of air-exposed TiFe-based hydrogen storage alloy

This study investigated how Fe substituted with Mn and Cr affected the microstructure and the first hydrogenation kinetics of a TiFe-based hydrogen storage alloy. Vacuum arc melting was used to prepare TiFe1-xMx ingots (M = Mn, Cr, x = 0.1, 0.2, 0.3). Thermodynamic calculations were performed to predict the phase formation behavior. The TiFe0.9Mn0.1 alloy was expected to form a single TiFe phase, and all other alloys were calculated to have dual-phase microstructures with TiFe and Laves phases. Based on the microstructure analysis results, the phase formation behaviors of the alloys showed a trend similar to the thermodynamic calculation results. The first hydrogenation kinetics was examined at room temperature (20 °C) with a hydrogen pressure of 40 bar. The samples for the kinetic analysis were prepared by crushing the ingots in air. The TiFe0.9Mn0.1 alloy with a single TiFe phase did not absorb hydrogen, while the alloys containing Laves phase absorbed hydrogen without any thermal activation process. As for the microstructure and kinetics analysis results, both the percentage and composition of the Laves phases affected the first hydrogenation kinetics.