Synchrotron XRD and XANES studies of cerium-doped NaAlH4: Elucidation of doping induced structure changes and electronic state

NaAlH4 samples doped with Ce additives, at various stages in a hydrogenation process, are investigated using synchrotron X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) spectroscopy. The presence of Ce–Al alloy regions are detected in the ball-milling samples, and no evidence of changes in the unit-cell dimensions of NaAlH4 are seen between ball-milling and hydrogenation samples. The XANES spectra of the samples are measured at the L-3 edge of the cerium, and by comparing the spectra of the dopants with those of the pure oxides, we find that a valency change of the oxidated states of cerium from Ce4+ to Ce3+.