Study of hydrogen storage and electrochemical properties of AB2-type Ti0.15Zr0.85La0.03Ni1.2Mn0.7V0.12Fe0.12 alloy

Abstract

A C15 AB2 Laves-type Ti0.15Zr0.85La0.03Ni1.2Mn0.7V0.12Fe0.12 alloy was prepared by arc melting and annealing. Phase-structural composition, microstructure, hydrogen absorption-desorption properties, thermodynamic and electrochemical performances were characterized by X-ray diffraction, scanning electron microscopy, hydrogen absorption-desorption measurements and electrochemical characterization and were related to the use of the alloys as metal hydride battery anodes.The alloy contains a C15 FCC intermetallic compound as the main phase and a LaNi secondary phase as the minor constituent (~ 1 wt.%).During the electrochemical tests, the anode electrodes quickly, after just a few activation cycles, reached a maximum discharge capacity. This was related to the catalytic effect of the La-rich secondary phase which acted as a catalyst of hydrogen absorption-desorption.Annealing resulted in increase of the maximum discharge capacity from 345 mAh/g for the as cast alloy to 370 mAh/g. Furthermore, the annealed alloy showed a better high rate dischargeability and a higher cyclic stability. After 100 cycles with 100% DOD at discharge current density of 1 C, the discharge capacity of the annealed alloy was very high, at a level of 90 % of the initial capacity.The rates of hydrogen diffusion have been characterized by Potentiostatic Intermittent Titration Technique and Electrochemical Impedance Spectroscopy. With increasing an extent of transformation into the hydride, the H diffusion rate in the bulk of the alloy particles decreased. The maximum value of DH measured by PITT for the annealed alloy was observed for the nearly fully discharged electrode, (SOC 2 %).

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

“…phases are based on Zr and/or Ti as the large A metal, while the B lattice sites are occupied by one or-in most cases-more of the 3d metals Co, Cr, Fe, Mn, Ni, V. The compositions of both the alloys with mainly Zr on the A sites (e.g., [434][435][436][437][438][439][440][441]) and with mainly Ti on the A sites (e.g., [442][443][444][445][446][447][448][449]) became more and more complex. Many of the currently discussed alloys for applications contain six to nine components, where in some cases small amounts of main group elements such as Al or Sn (e.g., [421,450,451]), or lanthanides [452] were added. More recently, also some multi-component, equiatomic or nearly equiatomic alloys (frequently called 'high-entropy alloys' (HEAs)) such as CoFeMnTi x V y Zr z (0.5 B x B 2.5, 0.4 B y B 3.0, and 0.4 B z B 3.0) [453], CrFeNiTiVZr [454] and CrFeMnNiTiZr [455] were studied with respect to their hydrogen storage properties (cf.…”

Studies of the effect of melt spinning on the electrochemical properties of the AB2 Laves phase alloys

“…The electrochemical characterization was carried out with a three-electrode-based CT 2001 Land Battery Tester,. The test details can be found elsewhere [9][10][11][12][13].…”

“…shows the phase compositions of the ascast and melt-spun samples with the C14-and C15-type alloys as obtained from the Rietveld refinements [9,10]. For the C14-type alloys, the higher speed of the melt spinner resulted in a larger abundance of the C14 phase which is probably caused by the tendency of the C14 Laves phase to preferably form at higher rotation wheel speeds and higher solidification rates [12]. Such effect is even more pronounces at higher speed of the melt spinner for the C15 phases leading even higher increased abundance.…”

Improving Reproducibility in Hydrogen Storage Material Research

“… [98] In this case, absorption occurs at higher pressures than desorption – see, for example, Figure 9 . [99] When both hydrogen absorption and desorption have been measured accurately, the hysteresis loop should close, at a finite pressure. If not, this indicates measurement problems, such as kinetic limitations or error accumulation.…”

“…Hydrogen absorption and desorption isotherms for an AB 2 alloy (Ti 0.15 Zr 0.85 La 0.03 Ni 1.2 Mn 0.7 V 0.12 Fe 0.12 ), measured in the range 293 K to 353 K, illustrating behavior typical for interstitial hydrides, including an increasing plateau pressure with increasing temperature and hysteresis between the absorption and desorption isotherms, particularly at the lower temperature. Reproduced with permission from Ref [99]…”