In Situ X-Ray Absorption Fine Structure Measurements of LaNi5 Electrodes in Alkaline Electrolytes

In situ Ni K-edge and La Lm-edge x-ray absorption fine structure (XAFS) measurements of LaNi5 electrodes supported on hydrophobic carbon black-polytetrafluoroethylene (PTFE) layers were carried out in strongly 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 identical to those reported earlier for crystalline LaNi5before and after exposure to gas-phase hydrogen, respectively. The Ni K-edge extended x-ray absorption fine structure (EXAFS) analysis of the most prominent shell yielded average Ni-Ni nearest neighbor distances of 2.52 ± 0.02 A for the charged compared to 2.47 ± 0.02 A for the discharged and uncharged electrodes. For the La Lm-edge XANES, the white line was found to be significantly more intense for the charged 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 hydrogen injection.