AMORPHOUS LA-NI THIN-FILM ELECTRODES

Amorphous La-Ni thin films over a wide range of composition were fabricated by electron beam evaporation in ultra-high vacuum. The structure and composition of these films were determined by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA). The reversible hydrogen storage capacity was determined by electrochemical cycling. The equilibrium electrochemical potential of these thin-film electrodes was also measured Versus the change of hydrogen concentration, Delta H/M, in these films. The smallest value among the maximum Delta H/M of these amorphous films is about 0.38, which is still much larger than the one reported in the literature (similar to 0.1). Harris's model for hydrogen absorption in amorphous transition metal alloys is applied to the amorphous La-Ni system. We found that both the La-Ni-3 and the La-2-Ni-2 type of tetrahedral sites can store hydrogen.