AMORPHOUS LA-NI THIN-FILM ELECTRODES

Amorphous La-Ni thin films over a wide range of composition were fabri cated 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 microa nalysis (EPMA). The reversible hydrogen storage capacity was determine d by electrochemical cycling. The equilibrium electrochemical potentia l 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, w hich is still much larger than the one reported in the literature (sim ilar to 0.1). Harris's model for hydrogen absorption in amorphous tran sition 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.