Electrochemical Properties Of Zrni_1.2 Mn_0.5cr_0.2v_0.1 And Zrni_1.2 Mn_0.45cr_0.2v_0.15 Alloy Electrodes Depending On Discharge Modes 

Abstract

The electrochemical properties of composite electrodes produced from ZrNi_1.2Mn_0.5Cr_0.2V_0.1 and ZrNi_1.2Mn_0.45Cr_0.2V_0.15 alloys with and without copper powder additions, pressed with alloy-to-copper weight ratios of 1 : 0.5 and 1 : 1, were studied under two discharge modes: discharge to a voltage of 0.85 and 0.7 V between the test electrode and the counter electrode. X-ray diffraction was employed to determine the phase composition of the alloys. An increase in vanadium content by ~1.3 wt.% led to a significant decrease in the amount of the Zr₇Ni₁₀ phase in the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 and ZrNi_1.2Mn_0.45Cr_0.2V_0.15 alloys (~17 and ~8 vol.%, respectively). The activation of the starting electrodes (without copper additions) depends on the amount of this phase with discharge to 0.85 V: the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy electrode, with a higher Zr₇Ni₁₀ content, activated faster. Composite electrodes from both alloys with 1 : 1 copper additions discharged to 0.7 V activated at the same rate within eight cycles, indicating that activation in these conditions does not depend on the Zr₇Ni₁₀ content. The substitution of manganese with vanadium slightly decreased the maximum discharge capacity of the electrodes (with and without copper powder additions) under both discharge modes. When discharged to 0.7 V relative to the Ni(ОН)₂ electrode (or ~0.4 V relative to the Hg/HgO electrode), both alloy electrodes, with and without copper powder additions, preserved their cyclic stability and showed accelerated activation compared to discharge at 0.85 V. The maximum discharge capacity was achieved with 1 : 1 copper additions and discharge to 0.7 V: 385 for the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy and 400 mA · h/g for the ZrNi_1.2Mn_0.45Cr_0.2V_0.15 alloy (versus ~280 mA · h/g at 0.85 V). Thus, a lower manganese content, along with an accordingly higher vanadium content (~1.3 wt.%), only slightly reduced the maximum discharge capacity of the electrodes and slowed their activation in the absence of catalytic additions. The activation of the starting electrodes produced from both alloys depends on the Zr₇Ni₁₀ content but does not depend on this phase in the case of 1 : 1 copper additions and discharge to 0.7 V.