DISCHARGE CAPACITY AND CORROSION RESISTANCE OF COMPOSITE ELECTRODES PRODUCED FROM ZrNi_1.2Mn_0.5Cr_0.2V_0.1  AND COPPER POWDERS

Abstract

Two samples of the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy were prepared using argon-arc melting. The samples differed in weight, resulting in distinct cooling modes, and their quantitative phase composition was determined with X-ray diffraction. The electrochemical properties of the alloy samples and the associated composite with a copper addition (in a 1 : 1 alloy-to-copper weight ratio) were studied in both potentiodynamic and galvanostatic modes in the cathodic and anodic potential regions. In particular, the hydrogen capacity and corrosion resistance of the samples discharged to a voltage of 0.7 V relative to the Ni(OH)₂ electrode  (~ 0.4 V relative to the Hg/HgO electrode) were evaluated. When discharged to 0.7 V, the activation of the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy electrodes accelerated as compared to 0.8 V and thus the discharge capacity in the first hydrogenation–dehydrogenation cycles increased significantly, while the maximum achieved discharge capacity of the composite depended on the number of Laves phases in the alloy. At 20 °C, the composite produced from the alloy with a higher Laves phase content (~ 90 vol. % С₁₄₊₁₅) activated three to four cycles sooner than the sample with a lower Laves phase content (~ 80 vol. % С₁₄₊₁₅) and achieved a higher discharge capacity of ~290 mA· h/g when discharged to 0.8 V. The discharge capacity of the composite discharged to 0.7 V relative to the Ni(OH)₂ electrode (~0.4 V relative to the Hg/HgO electrode) combined the contribution from the alloy via electrochemical hydrogenation–dehydrogenation processes and the contribution from copper via oxidation with anodic polarization. The passivation region on the corrosion curve over a wide range from the stationary potential to E = +0.5 V for the alloy section processed in a 30% KOH solution demonstrated the corrosion resistance of the alloy electrodes at a discharge voltage of –0.7 V, indicating the absence of selective dissolution of alloy components.