| 1. Effect of SDS on the electrochemical oscillation of nickel in HNO3/Cl-/ H2O solutionThe periodic current oscillation of nickel is investigated in 0.5mol·L-1 HNO3/0.005 mol·L-1 Cl-/H2O solution. During the current oscillation, there exist the oscillations of the structure of electronic double layer, the composition of surface film and Ni2+ concentration. The oscillations of the differential capacitance and conductance are detected by the potential and time scanning methods (two kinds of electrochemical impedance methods) for the first time, whose changing characteristics are the same as the periodical current oscillations. The current oscillations can be controlled by SDS concentration and the oscillation potential ranges reduce with the increase of SDS concentration. The periodical current oscillations disappear instead only one current oscillation appears when SDS concentration is more than 5.0×10-5 mol·L-1. The amplitude of the current oscillation and the passive differential capacitance as well as the conductance decrease with the increase of SDS concentration till the SDS concentration reaches 1.5×10-4 mol·L-1, which changes like the surface tension of the 0.5mol·L-1HNO3/0.005mol·L-1Cl-/SDS/H2O system. When the electrode potential is controlled at -0.4V(Vs. SCE), the adsorption of SDS on nickel surface obviously affects the electrochemical impedance spectroscopy. And the maximal phase angle, surface adsorption capacitance and the polarization resistance increase with the increase of SDS concentration. It can be interpreted by the adsorption of SDS, which enhances the electrode polarization and inhibits the charge transfer process. And this change doesn't terminate until the SDS concentration increase to 1.0×10-3 mol·L-1. When the electrode potential is controlled at 0V(Vs. SCE), the electrode is active. And with the increase of SDS concentration, the maximal phase angle, the polarization resistance and the adsorption and desorption inductance (L1, L2)... |
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