IN-SITU X-RAY-ABSORPTION FINE-STRUCTURE MEASUREMENTS OF LANI5 ELECTRODES IN ALKALINE ELECTROLYTES

In situ Ni K-edge and La L(m)-edge x-ray absorption fine structure (XA FS) measurements of LaNi5 electrodes supported on hydrophobic carbon b lack-polytetrafluoroethylene (PTFE) layers were carried out in strongl y alkaline electrolytes as a function of the state of charge. The Ni K -edge x-ray absorption near-edge structure (XANES) for the material in the discharged (and uncharged) and charged states were essentially id entical to those reported earlier for crystalline LaNi5 before and aft er exposure to gas-phase hydrogen, respectively. The Ni K-edge extende d x-ray absorption fine structure (EXAFS) analysis of the most promine nt shell yielded average Ni-Ni nearest neighbor distances of 2.52 +/- 0.02 Angstrom for the charged compared to 2.47 +/- 0.02 Angstrom for t he discharged and uncharged electrodes. For the La L(m)-edge XANES, th e white line was found to be significantly more intense for the charge d than for the uncharged LaNi5, an effect consistent with an increase in the density of empty d-like states just above the Fermi level on hy drogen injection.