Enhancing the Hydrogen Storage Properties of Ti-Mn Alloys by Ti Occupying Mn Sites: An Experimental and Theoretical Study

Striking a balance between hydrogen storage properties and cost is a challenge for Ti-Mn alloys. In this work, a strategy involving the utilization of inexpensive Ti to occupy Mn sites is employed to enhance the hydrogen storage properties of Ti-Mn alloys. The relationship between the composition, phases, electronic structure, and hydrogen storage properties of Ti1+xMn2-x (x = 0.20, 0.25, 0.30, 0.35, 0.40, and 0.45) alloys is investigated systematically. The experiments demonstrate that the substitution ratio x of Ti occupying Mn sites is between 0.25 and 0.3. Once exceeded, the alloys gradually precipitate the alpha TiMn and beta Ti phases. All of the alloys do not require high-temperature activation. The Ti1.25Mn1.75 alloy exhibits the highest reversible hydrogen storage capacity of 1.94 wt % under 25 degrees C and 6 MPa. The first-principles calculation reveals that the partial substitution of Ti for Mn changes the electronic structure of the alloy and lowers the solid solution energy of H atoms within the interstitial sites of the alloy. This accounts for the observed decrease in the alloy plateau pressure following the partial substitution of Ti for Mn. This research provides valuable insights into the design of high-performance Ti-Mn hydrogen storage alloys using inexpensive elements.