Gaseous phase and electrochemical hydrogen storage properties of ti50 zr1 ni44 x5 (X = ni, cr, mn, fe, co, or cu) for nickel metal hydride battery applications

Abstract

Structural, gaseous phase hydrogen storage, and electrochemical properties of a series of the Ti50 Zr1 Ni44 X5 (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 Ti2 Ni secondary phase. Improvement in synergetic effects between the main TiNi and secondary Ti2 Ni phases, determined by the amount of distorted lattice region in TiNi near Ti2 Ni, 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 Ti50 Zr1 Ni49 base alloy. Capacity performance is further enhanced in the electrochemical environment, especially in the cases of the Ti50 Zr1 Ni49 base alloy and Ti50 Zr1 Ni44 Co5 alloy. Although the TiNi-based alloys in the current study show poorer high-rate performances compared to the commonly used AB5, AB2, and A2 B7 alloys, they have adequate capacity performances and also excel in terms of cost and cycle stability. Among the alloys investigated, the Ti50 Zr1 Ni44 Fe5 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.