Effects of Vanadium/Nickel Contents in Laves Phase-Related Body-Centered-Cubic Solid Solution Metal Hydride Alloys

Ouchi²,

Nei³

et al. 2017

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A combination of analytic tools and electrochemical testing was employed to study the contributions of Palladium (Pd) in a Zr-based AB 2 metal hydride alloy (Ti 12 Zr 22.8 V 10 Cr 7.5 Mn 8.1 Co 7 Ni 32.2 Al 0.4 ). Pd enters the A-site of both the C14 and C15 Laves phases and shrinks the unit cell volumes, which results in a decrease of both gaseous phase and electrochemical hydrogen storage capacities. On the other hand, the addition of Pd benefits both the bulk transport of hydrogen and the surface electrochemical reaction. Improvements in high-rate dischargeability and low-temperature performances are solely due to an increase in surface catalytic ability. Addition of Pd also decreases the surface reactive area, but such properties can be mediated through incorporation of additional modifications with rare earth elements. A review of Pd-addition to other hydrogen storage materials is also included.

Section: Pct Analysissupporting

confidence: 64%

Increase in the Surface Catalytic Ability by Addition of Palladium in C14 Metal Hydride Alloy

Ouchi²,

Nei³

et al. 2017

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“…By comparing the compositions of alloys C14 and C15 (Table 4), Cr, a very important substitution element in the MH alloy for the enhancement of corrosion resistance by forming the V-Cr-based solid solution secondary phase [78,99], is absent in alloy C15. Alloy C15 also has a higher Ni-content, which is known for achieving a better HRD performance [100,101]. While the Cr-containing alloy C14 is more difficult to activate but maintains the discharge capacity in the first 13 cycles, the Cr-free alloy C15 shows some capacity degradation.…”

Section: Electrochemical Analysismentioning

confidence: 99%

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

Nei²,

Wan

et al. 2017

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Abstract:Herein, we present a comparison of the electrochemical hydrogen-storage characteristics of two state-of-art Laves phase-based metal hydride alloys (Zr 21.5 (V and Cr) in the first composition results in an average electron density below the C14/C15 threshold ( e/a ∼ 6.9) and produces a C14-predominated structure, while the average electron density of the second composition is above the C14/C15 threshold and results in a C15-predominated structure. From a combination of variations in composition, main phase structure, and degree of homogeneity, the C14-predominated alloy exhibits higher storage capacities (in both the gaseous phase and electrochemical environment), a slower activation, inferior high-rate discharge, and low-temperature performances, and a better cycle stability compared to the C15-predominated alloy. The superiority in high-rate dischargeability in the C15-predominated alloy is mainly due to its larger reactive surface area. Annealing of the C15-predominated alloy eliminates the ZrNi secondary phase completely and changes the composition of the La-containing secondary phase. While the former change sacrifices the synergetic effects, and degrades the hydrogen storage performance, the latter may contribute to the unchanged surface catalytic ability, even with a reduction in total volume of metallic nickel clusters embedded in the activated surface oxide layer. In general, the C14-predominated alloy is more suitable for high-capacity and long cycle life applications, and the C15-predominated alloy can be used in areas requiring easy activation, and better high-rate and low-temperature performances.

“…Details of the melting process were reported before [25,26]. The main difference between these two preparation methods is the size of ingot.…”

Section: Experimental Set-upmentioning

confidence: 99%

Effects of Alkaline Pre-Etching to Metal Hydride Alloys

Meng¹,

Hu³

et al. 2017

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Abstract:The responses of one AB 5 , two AB 2 , four A 2 B 7 , and one C14-related body-centered-cubic (BCC) metal hydrides to an alkaline-etch (45% KOH at 110 • C for 2 h) were studied by internal resistance, X-ray diffraction, scanning electron microscope, inductively coupled plasma, and AC impedance measurements. Results show that while the etched rare earth-based AB 5 and A 2 B 7 alloys surfaces are covered with hydroxide/oxide (weight gain), the transition metal-based AB 2 and BCC-C14 alloys surfaces are corroded and leach into electrolyte (weight loss). The C14-predominated AB 2 , La-only A 2 B 7 , and Sm-based A 2 B 7 showed the most reduction in the internal resistance with the alkaline-etch process. Etched A 2 B 7 alloys with high La-contents exhibited the lowest internal resistance and are suggested for use in the high-power application of nickel/metal hydride batteries.