PHOTOELECTROCHEMICAL STUDY OF PASSIVE LAYERS ON COPPER ELECTRODES IN SOME ALKALINE MEDIA

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The electrochemical behavior of Cu electrodes in alkaline solutions with and without argongas purging was studied by cyclic voltammetry and the photocurrent response method. In Na2SO4 solution (pH 9.1), the electrode shows a ptype photoresponse initially, which changes to an ntype when pitting corrosion occurs, at potentials more positive than the critical breakdown potential. The cathodic photocurrent is much larger in stronger alkaline solutions, e. g.,0.1 mol/L KOH solution, reflecting a more porous structure of Cu2O layer on the electrode surface in strong alkaline solutions. Additionally, the cathodic current is larger in deaerated solutions than that in nondeaerated solutions. While the initiation of CuO formation on the electrode may not be obvious on the currentvoltage curve, it can be obtained from the photocurrentvoltage curve where it corresponds to the onset of the decrease in the photocurrent on the positive potential scan.