Multicomponent Alloys from the Ti–Nb–Cr System for Hydrogen Storage Derived from Ti Alloy Scraps

The growing demand for renewable energy has intensified interest in hydrogen as an energy vector. Metal hydrides are promising solid-state hydrogen carriers due to their high volumetric storage density and improved safety. Multicomponent alloys capable of forming metal hydrides allow tuning of the hydrogen storage properties through compositional design. However, most reported hydrides are produced from high-purity primary metallic elements, involving energy-intensive processes and a significant environmental impact. Replacing primary elements with metal scraps and reducing the use of high-carbon-emission elements are effective strategies to lower the environmental footprint of metallic materials. In this context, this work demonstrates a sustainable alloy design strategy for body-centered cubic (BCC) hydrogen storage alloys by replacing primary titanium with Ti-based alloy scraps and eliminating the use of primary vanadium, a high-carbon-emission element. Two types of titanium alloy scraps were used: machining chips of commercially pure Ti grade 2 (ASTM F67) combined with high-purity Nb and Cr and machining chips of Ti6Al4V ELI (ASTM F136) combined with commercially available Nb and Cr. Based on compositional and microstructural analyses, Ti33Nb33Cr33 (from Ti grade 2 scraps) and Ti32Al2V1Nb37Cr28 (from Ti6Al4V ELI scraps) were selected for detailed investigation. Equivalent CO2 emissions (CO2-eq) of the feedstock materials were estimated using a life-cycle assessment framework, revealing that substituting primary Ti with secondary Ti reduces emissions from ∼8 to ∼5 kg CO2-eq/kg alloy. Both alloys exhibited BCC microstructures and hydrogen storage capacities of 2.25 and 2.50 wt % H, respectively, with approximately 1 wt % H reversibly absorbed and desorbed at room temperature. These results demonstrate that environmentally optimized feedstock selection can reduce carbon footprint without compromising reversible hydrogen storage performance, providing a viable pathway toward more sustainable metal hydride systems.