Effect of Halide Anions on Anodic Behaviour and Passivation of Copper in Alkaline Media

The effect of Cl- and Br- on the anodic behaviour and passivation of copper metal in NaOH solution has been investigated by a potentiodynamic technique complemented with XPS analysis. In halide free solutions, the anodic polarization curves involve three anodic peaks correlated to the electroformation of Cu2O, CuO and Cu(OH)2 on the anode surface. The presence of these species in the passive layer has been confirmed by XPS examination. An addition of the halide anions enhances the peak currents of anodic peaks and tends to rupture the passive layer inducing the pitting corrosion. The critical pitting potentials decrease with rising halide concentration while the alkali concentration has an opposite effect. The accelerating effect of Cl- to pitting corrosion is greater than that of Br-. The pitting corrosion was explained by an instantaneous nucleation and growth of anion salt nuclei. Three cathodic peaks on cyclic voltammetric curve were assigned to the electroreduction of pitting corrosion products, Cu(II) and Cu(I) oxides, respectively.

A New Charge Storage Mechanism for Electrochemical Capacitors and Charge Storage Density Vs. Crystalline Structure of Metal Oxides

ABSTRACTThe hydrous ruthenium oxide (RuO2.xH2O) powders with different contents of H20 have been formed by a sol-gel process and have been annealed at different temperatures. It was found that the specific capacitance of RuO2.xH2O is strongly dependent on the crystalline structure. The specific capacitance of over 720 F/g was obtained in an amorphous RuO2.xH2O. This value is at least two times greater than ever reported of this type of material.The specific capacitance dropped rapidly as the amorphous phase transforms into the crystalline phase at high temperatures. In contrast to the crystalline phase the specific capacitance of an amorphous RuO2.xH2O was not dependent on the specific surface area. The charge storage mechanism in amorphous RuO2.xH2O is different from that in the crystalline RuO2. The current in the cyclic voltammetric curve of RuO2.xH2O is nearly constant and is symmetrical with the potential in a range of 1 volts. The resistivity of pellets made from these powders is in the order of 10−3 Ω-cm.