Electrochemical characteristics of La-Ni-Al thin films

AB₅ based hydrogen storage thin films (LaNi_4.25Al_0.75), deposited on Cu substrate by dc magnetron sputtering, have been investigated in this paper. X-ray diffraction (XRD) revealed that the microstructure of the film was in crystal form. SEM, AFM and FIB analyses proved that on the surface there were many pores of approximately 15-40 nm in diameter of random size. The cross section of the film revealed that it was rather dense and defect-free, with a uniform thickness of about 4.2 μm. Electrochemical properties of the films were measured by simulated battery tests. The single layer LaNi_4.25Al_0.75 film undergoes a longer activation period than typical AB₅ alloys in bulk and the maximum discharge capacity of the film was about 220 mAh/g. Two electrochemical behaviour (distinct to the bulk materials) were observed for the film electrode in which there was an apparent increase in intermediate potential for each discharge process, as well as a local increase of discharge potential during its activation period.