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.
Studies in molybdenum/manganese content in the dual body-centered-cubic phases metal hydride alloys
Abstract A series of TiVCrMn-based body-centered-cubic (BCC) alloys with design compositions of Ti40V30Cr15Mn15−xMox, where x = 0, 2, 4, 6, 8, 10, and 12, were prepared by an arc melter. Their microstructures were characterized and compared to the hydrogen storage properties in both gaseous phase and electrochemistry. X-ray diffraction results indicate the alloys are dominated by either one (x = 0 and 2) or two BCC phases (x = 4 to 12). As the Mo-content in the alloy increases, much of the first BCC phase is replaced by the second BCC phase with a stronger metal–hydrogen bond, lattice constant of the first BCC phase increases while that of the second BCC phase remains about the same, and both gaseous and electrochemical hydrogen storage capacities and plateau pressure increases and then decreases. The boundary between the two BCC phases is found to be crucial for the hydrogen storage properties. Alloy with a composition of Ti40V30Cr15Mn11Mo4 shows a good balance among various electrochemical properties, and alloys with higher Mo-contents (8 at% for example) achieved discharge capacity up to 639 mAh g−1 at 4 mA g−1 but are less stable in 30% KOH due to cracking and surface oxidation. Using higher concentration of KOH at 50% as the electrolyte is able to improve 8 at% Mo-containing alloy by nearly 60% by reducing the adverse effect from passivation.
Recalculation of Mass Defects
THE well-known mass defect curve of the old nuclear scheme calculated with regard to α-particles and protons presented a difficulty with its minimum of binding energy for tin and an increasing portion between tin and lead. On the other hand, the mass defect values against protons give a rather smoothly decreasing curve.1 As has already been pointed out,2 the number of α-particles must be considerably reduced from the point of view of the new scheme, which does not admit any electrons in nuclei, but only neutrons and protons (presumably joined as α-particles). The curve of mass defect against protons and neutrons (perhaps with a single ‘central’ α-particle) is very similar to the old curve against protons, but decreases less rapidly. Clearly the new mass defect values relatively to α-particles, neutrons and protons must lie somewhere between the old values computed relative to protons and α-particles respectively (because the number of α-particles is decreased). We may emphasise that this new mass defect curve shows no increasing portion between tin and lead. For illustration we give two typical values: Old: 50Sn124 = 31α + 12&#38;epsiv;; mass defect = 0.158 (in mass units); 82Pb208 = 52α + 22&#38;epsiv;; mass defect = 0.035. New: 50Sn124= 25α + 24ω (ω = neutron); mass defect = 0.304; 82Pb208 = 41α + 44ω; mass defect = 0.366.