ZRV1.5NI1.5 AS ELECTRODE MATERIAL IN NICKEL-METAL HYDRIDE BATTERIES -AN IN-SITU SCANNING-TUNNELING-MICROSCOPY INVESTIGATION

We have investigated the alloy ZrV1.5Ni1.5 by means of scanning electr on microscopy (SEM) with electron probe X-ray microanalysis (EPMA), X- ray diffraction (XRD), in situ STM (scanning tunnelling microscopy in an electrolyte under controlled electrochemical potential) and electro chemical charge discharge measurements. By means of EPMA we found that the alloy is composed of three different crystallographic phases. The main phase (approximate to 75 vol.%) is ZrV0.81Ni1.47 the second phas e (approximate to 20 vol.%) is V92Ni8 and the third (approximate to 5 vol.%) is a ZrNi based phase. Using in situ STM we investigated the di fferent corrosion behaviour of the phases. At a potential of -600 mV v ersus the Hg/HgO reference electrode we observed the corrosion of the vanadium rich phase while the other two phases passivated. (C) 1997 El sevier Science S.A.