Electrochemical Behavior of α-Phase of the Cu30Ni System in Sodium Hydroxide Solutions

Abstract

Electrochemical behavior of a hydrogenized Cu30Ni alloy in 1 N NaOH solution was studied by using standard and cyclic voltammetry, chronocoulo-, ampero-, and potentiometry. Anodic polarization of the initial alloy results in the copper selective dissolution; that of the hydrogenized alloy, in the hydrogen selective ionization. The anodic current peak observed at E = -0.5 V in the cyclic voltammograms and anodic polarization curves of the hydrogenated alloy is caused by the hydrogen ionization. The peak is controlled by the hydrogen diffusion in the solid. The volume capacitance of the alloy in hydrogen significantly exceeds that of nickel. It is shown that the hydrogen ionization is practically reversible; unlike nickel, the alloy chronopotentiograms taken at i = const do not break up after a short initial potential arrest but descend, gradually as a result of ionizing the absorbed hydrogen. SHORT COMMUNICATIONS

Corrosion of Hydrides of Nickel and Cu30Ni Alloy in Oxygen Containing Solutions

“…6a, curve 3), as well as the difference in their corrosion rates, suggests that the alloy hydride contains a smaller amount of hydrogen capable of reacting with oxygen compared with nickel hydride. This can be caused by quicker decomposition of the alloy hydride [12] compared with nickel hydride, which can apparently result in molization of some hydrogen atoms adsorbed at the alloy surface. As a result, only a part of hydrogen reacts with oxygen, and the potential delay in E c vs. t curve of alloy hydride is shorter compared with nickel hydride.…”

The Electrochemical Behavior of β-Phase in the Cu30Ni-H System in Sodium Hydroxide Solutions

“…Partial substitution of copper for nickel makes the hydride phase more stable and significantly enhances the hydrogen absorption by the alloy. Therefore, we aimed at studying the electrochemical behavior of Cu30Ni alloy hydride in alkaline solutions and interpreting it taking into account our former data on the electrochemical behavior of hydrogenated copper [4] and nickel [5,6] and nickel hydride as well [7,8].The experiments were carried out in 1 N NaOH solution in N 2 (of PNG grade) atmosphere at 20 ° C. Prior to the experiments, the alloy was cleaned with emery paper, degreased, and rinsed with twice-distilled water. The hydride ( β -phase) was synthesized in 1 N H 2 SO 4 + 0.2 g/l thiourea solution under cathodic polarization ( i h = 500 A/m 2 , t h = 1 h) [9].…”

“…Partial substitution of copper for nickel makes the hydride phase more stable and significantly enhances the hydrogen absorption by the alloy. Therefore, we aimed at studying the electrochemical behavior of Cu30Ni alloy hydride in alkaline solutions and interpreting it taking into account our former data on the electrochemical behavior of hydrogenated copper [4] and nickel [5,6] and nickel hydride as well [7,8].…”

“…From the shape of the curve 2 it follows that the alloy hydride decomposition kinetics can be studied only in a potential range more negative than -0.3 V; at less negative potentials copper dissolution occurs [4]. Therefore, the cyclic voltammogram (CVA) method appeared to be most appropriate, like in the case of nickel hydride [7,8].…”

“…1 we show cathodic and anodic VACs of the hydrogenated alloy ( α -phase) (curve 1 ) [10] and of the alloy hydride ( β -phase) (curve 2 ) recorded by shifting the potential in the positive direction by steps of 0.01 V. The onset of hydrogen evolution at the hydride is observed at a potential by 0.2 V more negative than at the α -phase; oxygen evolution does not depend on the hydrogen content in the alloy. Cathodic voltammetric curves of the alloy hydride contain a cathodic limiting current plateau at -0.9 to -0.35 V like that for nickel hydride [7,8].…”