Effect of cycling conditions on hydride stability of the Ti11Nb61Cr28 alloy

Abstract

Hydrogen is a promising clean energy carrier, but its safe and efficient storage and transportation remain significant challenges. Metal hydrides, particularly body-centered cubic (BCC) alloys, offer a potential solution, enabling the fine-tuning of their properties through chemical composition control. The Ti₁₁Nb₆₁Cr₂₈ BCC alloy exhibits an absorption plateau pressure of approximately 1 bar at room temperature, representing a step toward improving reversibility within the Ti-Nb-Cr system. However, capacity loss during cycling still hinders the broader application of BCC alloys for hydrogen storage. In this study, the cycling-induced modifications in the Ti₁₁Nb₆₁Cr₂₈ alloy were investigated after cycling with desorption at 350 °C and 25 °C. X-ray diffraction revealed that, upon the first hydrogenation, a predominant face-centered cubic (FCC) hydride is formed and remains stable for extended periods under ambient conditions. Cycling with desorption at 350 °C, which promotes complete desorption in each cycle, led to the hydride destabilization, evidenced by extensive spontaneous desorption over time under ambient conditions and the formation of an intermediate face-centered orthorhombic (FCO) phase over slow desorption. In contrast, the FCC hydride formed after cycling at 25 °C remained stable without FCO phase formation. SEM analysis revealed that cycling with complete desorption at 350 °C produced finer particles compared to the other conditions, which may play a crucial role in reducing the concentration of defects that act as hydrogen traps, thereby influencing hydride stability.