Anodic reactions of several reducing agents on illuminated cadmium sulfide electrode

Anodic reactions of several reducing agents occurring in competition with the electrode dissolution at an illuminated CdS electrode were studied under the potentiostatic condition. S²⁻, SO²⁻₃, and S₂O²⁻₃ ions, which can effectively suppress the photoanodic dissolution of CdS, shift the flatband potential of this electrode to the cathodic direction, leading to the shift of the onset potential for the anodic photocurrent. This shift is attributed to the adsorption of these ions on the electrode surface. Two- or three-step wave appeared in the photoanodic polarization curves in the electrolytes containing low concentration of these ions. The mechanism for these electrodic reactions was discussed in detail in terms of the energy band structure. It can be concluded that the reducing agents which interact so strongly with the CdS electrode surface that the energy band structure at the electrode/electrolyte interface is changed can suppress effectively the photoanodic dissolution of the electrode. The tendency of this interaction was S²⁻ > SO²⁻₃ > S₂O²⁻₃.