Hydride Destabilization in the Ti–Nb–Cr System Through Nb/Ti Ratio Adjustment

Hydrogen stands out as a promising substitute to fossil fuels amidst growing concerns over depleting reserves and environmental impacts. However, efficient hydrogen storage remains a critical challenge for widespread application. Solid-state storage, particularly utilizing metal hydrides (MH), is a promising method for efficient storage at reduced pressures. However, to increase the efficiency of the MH-based hydrogen storage system, it becomes crucial for hydrogen desorption to occur at lower temperatures. In this context, this study explores the destabilization of the hydrides of the Ti–Nb–Cr system by decreasing the concentration of the stronger hydride-forming element, Ti, while increasing the fraction of the weaker hydride-forming element, Nb. To achieve a predominant body-centered cubic (bcc) phase, the Cr content was maintained below 35 at. %. Four compositions were studied, namely Ti1.0Nb1.0Cr1.0, Ti0.8Nb1.4Cr1.0, Ti0.6Nb1.8Cr1.0, and Ti0.4Nb2.2Cr1.0. The alloys were synthesized via arc melting and predominantly consist of bcc phase with a fraction of C15 Laves Phase. All alloys exhibited rapid absorption kinetics at 25 °C and reversible hydrogen storage at 100 °C, with reversible capacities of 1.31, 1.25, 1.25, and 1.08 wt %, as the Nb/Ti ratio increases. Notably, only the Ti0.4Nb2.2Cr1.0 exhibited reversibility at 25 °C, with a reversible capacity of 1.22 wt %. Pressure–Composition–Temperature diagrams revealed that increasing the Nb/Ti ratio led to higher plateau pressures, reaching almost 1 bar in absorption for the Ti0.4Nb2.2Cr1.0 alloy. Moreover, thermal analysis measurements revealed that the enthalpy of desorption becomes less positive as the Nb/Ti ratio increases, providing evidence of the destabilization of the hydrides.