Gaseous Phase and Electrochemical Hydrogen Storage Properties of Ti₅₀Zr₁Ni₄₄X₅ (X = Ni, Cr, Mn, Fe, Co, or Cu) for Nickel Metal Hydride Battery Applications

Structural, gaseous phase hydrogen storage, and electrochemical properties of a series of the Ti₅₀Zr₁Ni₄₄X₅ (X = Ni, Cr, Mn, Fe, Co, or Cu) metal hydride alloys were studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed the multi-phase nature of all alloys, which were composed of a stoichiometric TiNi matrix, a hyperstoichiometric TiNi minor phase, and a Ti₂Ni secondary phase. Improvement in synergetic effects between the main TiNi and secondary Ti₂Ni phases, determined by the amount of distorted lattice region in TiNi near Ti₂Ni, was accomplished by the substitution of an element with a higher work function, which consequently causes a dramatic increase in gaseous phase hydrogen storage capacity compared to the Ti₅₀Zr₁Ni₄₉ base alloy. Capacity performance is further enhanced in the electrochemical environment, especially in the cases of the Ti₅₀Zr₁Ni₄₉ base alloy and Ti₅₀Zr₁Ni₄₄Co₅ alloy. Although the TiNi-based alloys in the current study show poorer high-rate performances compared to the commonly used AB₅, AB₂, and A₂B₇ alloys, they have adequate capacity performances and also excel in terms of cost and cycle stability. Among the alloys investigated, the Ti₅₀Zr₁Ni₄₄Fe₅ alloy demonstrated the best balance among capacity (394 mAh·g⁻¹), high-rate performance, activation, and cycle stability and is recommended for follow-up full-cell testing and as the base composition for future formula optimization. A review of previous research works regarding the TiNi metal hydride alloys is also included. View Full-Text