IN-SITU LA, CE, AND ND L-EDGE X-RAY-ABSORPTION FINE-STRUCTURE STUDY OF AN INTERMETALLIC METAL HYDRIDE ELECTRODE IN AN OPERATING ALKALINE BATTERY

The x-ray absorption fine structure of a technologically important MmL (5) intermetallic compound (Mm = La0.52Ce0.34Nd0.10Pr0.04, L(5) = Ni3. 5Ca0.8Mn0.3Al0.4) in the form of a hydrogen storage cathode was record ed in situ in the region 5440-6290 eV using an electrochemical cell wh ich is essentially a fully functioning alkaline battery. Significant d ifferences were observed in the x-ray absorption near edge structure ( XANES) of all of the absorption edges (La, Ce, and Nd) between the unc harged and fully charged states. In particular, a clear increase in th e intensity of the La and Nd L(III)-edge resonances (due to 2p(3/2) -- > 5d electronic transitions) was found upon charging the cell. This ph enomenon was attributed to an increase in the density of empty d-like states near the Fermi level following hydrogen injection into the latt ice. Furthermore, the behavior of the Ce L(II,III)-edges of this batte ry material upon charging was nearly the same as that observed for the gas phase hydrogenation of the Ce2Fe17 and Ce2Fe14B intermetallics re ported in the literature.