Effects of Alkaline Pre-Etching to Metal Hydride Alloys

Abstract

The responses of one AB5, two AB2, four A2B7, 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 AB5 and A2B7 alloys surfaces are covered with hydroxide/oxide (weight gain), the transition metal–based AB2 and BCC-C14 alloys surfaces are corroded and leach into electrolyte (weight loss). The C14-predominated AB2, La-only A2B7, and Sm-based A2B7 showed the most reduction in the internal resistance with the alkaline-etch process. Etched A2B7 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.

Keywords

• metal hydride alloy
• nickel metal hydride battery
• alkaline bath
• high rate performance
• superlattice alloys
• surface morphology