The Influence of Different Nickel Types on the Electrochemical Characteristics of the ZrNiMnCrV Alloy

The electrochemical characteristics (activation rate, cyclic stability, and capability to restore the discharge capacity and cyclic stability after a break in cycles) possessed by three samples of the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy doped with cathode, rolled cathode, and electrolytic nickel were studied. The impurity content was determined by emission spectral analysis. There were virtually no impurities (except for magnesium and titanium traces) in cathode nickel. In rolled cathode nickel, the largest number of impurities (magnesium and aluminum traces, 0.1 wt.% titanium, 0.1 wt.% copper, 0.1 wt.% silicon, and 0.2 wt.% iron) was revealed. In electrolytic nickel, the largest amount of iron impurities (>1 wt.%) was found. The experiments were performed with electrodes both without and with additions of carbonyl nickel powder (50 and 100% of the electrode weight) used as a catalyst of the electrochemical reaction. The electrodes produced from the alloy samples doped with cathode and rolled cathode nickel showed similar electrochemical behavior, differing significantly from the behavior of the electrodes produced with electrolytic nickel. Thus, the two former electrodes without nickel powder additions activated at 30 °C for three cycles and reached a discharge capacity of 256 and 280 mA∙h/g and that doped with electrolytic nickel activated for six cycles and reached 242 mA∙h/g. Nickel additions amounting to 50 and 100% of the electrode weight to the electrodes produced from samples with cathode and rolled cathode nickel significantly accelerated their activation at 15°C and had almost no effect on the activation at 30°C because it proceeded very quickly at this temperature (for three cycles). An ambiguous effect of catalytic additions in the case of electrodes produced with electrolytic nickel both at 15°C and 30°C (mainly accelerated activation) was revealed. Emission spectral analysis data suggest that this effect is probably due to a relatively large iron amount in the electrolytic nickel, resulting in less stable surface. Depending on the experimental temperature and the presence of activating additions, the discharge capacity of the electrodes produced with cathode and rolled cathode nickel after a breakin the cycles for five days either completely restored or slightly increased. The discharge capacity of the electrodes produced with electrolytic nickel significantly decreased when there was no catalytic addition and practically recovered when it was present. The electrodes produced with cathode and rolled cathode nickel were characterized by a constant rate of loss in the discharge capacity before and after a break in the cycles both at 15°C and 30°C (~0.7 mA∙h/g per cycle), in contrast to the electrodes with electrolytic nickel, whose lost in the discharge capacity was 1.14–1.3 mA∙h/g per cycle and increased to 5.0 mA∙h/g per cycle after a break. The electrode produced with cathode nickel and 50% nickel powder addition, preliminary held in a 30% KOH solution for five days, showed similar discharge capacity and better cyclic stability at 15°C than the electrode at 30°C after a break in the cycles.