ZrV1.5Ni1.5 as electrode material in nickel-metal hydride batteries An in situ scanning tunnelling microscopy investigation

We have investigated the alloy ZrV_1.5Ni_1.5 by means of scanning electron 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 electrochemical charge discharge measurements. By means of EPMA we found that the alloy is composed of three different crystallographic phases. The main phase (≈75 vol.%) is ZrV_0.81Ni_1.47, the second phase (≈20 vol.%) is V₉₂Ni₈ and the third (≈5 vol.%) is a ZrNi based phase. Using in situ STM we investigated the different corrosion behaviour of the phases. At a potential of ?600 mV versus the Hg/HgO reference electrode we observed the corrosion of the vanadium rich phase while the other two phases passivated.