Structure, Hydrogen Storage, and Electrochemical Properties of Body-Centered-Cubic Ti40V30Cr15Mn13X2 Alloys (X = B, Si, Mn, Ni, Zr, Nb, Mo, and La)

Abstract

Structure, gaseous phase hydrogen storage, and electrochemical properties of a series of TiVCrMn-based body-centered-cubic (BCC) alloys with different partial substitutions for Mn with covalent elements (B and Si), transition metals (Ni, Zr, Nb, and Mo), and rare earth element (La) were investigated. Although the influences from substitutions on structure and gaseous phase storage properties were minor, influences on electrochemical discharge capacity were significant. The first cycle capacity ranged from 16 mAh•g −1 (Si-substituted) to 247 mAh•g −1 (Mo-substituted). Severe alloy passivation in 30% KOH electrolyte was observed, and an original capacity close to 500 mAh•g −1 could possibly be achieved by Mo-substituted alloy if a non-corrosive electrolyte was employed. Surface coating of Nafion to the Mo-substituted alloy was able to increase the first cycle capacity to 408 mAh•g −1 , but the degradation rate in mAh•g −1 •cycle −1 was still similar to that of standard testing. Electrochemical capacity was found to be closely related to BCC phase unit cell volume and width of the an extra small pressure plateau at around 0.3 MPa on the 30 °C pressure-concentration-temperature (PCT) desorption isotherm. Judging from its high electrochemical discharge capacity, Mo was the most beneficial substitution in BCC alloys for Ni/metal hydride (MH) battery application.

Comparison of C14- and C15-Predomiated AB2 Metal Hydride Alloys for Electrochemical Applications

“…Compared to the C14 alloy, the PCT isotherms of both the C15 and C15A alloys show a very steep takeoff from the α (metal)-to-β (metal hydride) region, which is similar to the observations seen in Nd-based AB 5 [85] and A 2 B 7 [86] MH alloys, and a lower self-discharge is expected. Moreover, the C15 and C15A alloys show very flat plateaus, which are extremely uncommon in multi-phase MH alloys [8,87]. In order to quantify the plateau flatness, slope factor (as previously defined in [8]: the ratio of storage capacity between 0.01 MPa and 0.5 MPa to total capacity in the desorption isotherm) of each alloy was calculated.…”

Hydrogen Storage Characteristics and Corrosion Behavior of Ti24V40Cr34Fe2 Alloy

“…Literature indicates that annealing increases hydrogen capacity [13,14]. The BCC phase enhances hydrogen capacity [11,22,29]; an increase in its unit cell volume implies the availability of more hydrogen absorption sites or spaces, leading to an increase in storage capacity. The Laves phase is detrimental to storage capacity [10,[38][39][40], and alloys with larger Laves unit cell volumes or high Laves proportions are known to exhibit lower hydrogen capacity.…”

“…Although BCC solid solution alloys have very high gaseous phase hydrogen storage capacities, they suffer from severe capacity degradation during electrochemical applications due to the leaching of Vanadium (V) into the KOH electrolyte [21,22]. The preferential leaching of V in the negative electrode material has been previously identified [23], and V-free Laves phase alloys have been adopted to mitigate the consequent cycle life and self-discharge issues originating from V-corrosion [24,25].…”

Effects of Alkaline Pre-Etching to Metal Hydride Alloys

“…One of its key applications is the rechargeable nickel/metal hydride (Ni/MH) battery, which is used widely in consumer electronics, as well as stationary and transportation energy storage areas. A large variety of IMCs have been used/proposed as the active materials in the negative electrode of Ni/MH battery, such as A 2 B [2], AB [3,4], AB 2 [5], AB 3 [6], A 2 B 7 [7], A 5 B 19 [8], AB 5 [9], body-centered-cubic (BCC) solid solution [10], and their combinations [11,12]. These IMCs are composed of mostly transition metals (TM), and some may contain rare-earth (RE) elements.…”