Effects of Alkaline Pre-Etching to Metal Hydride Alloys

Resumen

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.