Transmission electron microscope studies in the surface oxide on the La-containing AB2 metal hydride alloy

La-addition to a Laves-phase based AB(2) metal hydride alloy improves the high-rate discharge and -40 degrees C charge-transfer resistance significantly. Surface oxide formation and embedded Ni inclusions of the alloy were studied using magnetic susceptibility, BET surface area and pore size measurements, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). BET measurements correlate with the double-layer capacitance measured at -40 degrees C, indicating a factor 3 increase in surface area with 5 at.% La replacement of Zr. Surface catalytic ability of the same alloy improves by a factor of 13. TEM reveals the surface of the La-free sample as lightly oxidized Ni, Ti, and Zr, while the La-containing sample is randomly distributed and heavily-oxidized (Ni, Cr)O-x coating the grain/oxide channel wall. These catalytic channels are believed to be the source of improvement in the low-temperature performance of these La-containing AB(2) metal hydride alloys. (C) 2016 Elsevier B.V. All rights reserved.