Impedance measurement of thin film SnO2 electrode in a sodium sulfate electrolyte containing SnSO4

Electrochemical impedance of thin film SnO2 electrodes under anodic polarization was measured in 0.2 mol dm(-3) Na2SO4 solutions with and without containing SnSO4. From the semi-circle plots on a complex impedance plane, the electrode interface conductivity, sigma(E) was calculated, which represents the easiness of the electron tunneling through the space charge layer of the SnO2 electrode. It was found that the interface conductivity of the SnO2 film electrode measured in the electrolyte containing SnSO4 is lower than that without SnSO4. This fact was ascribed to the SnO2 layer formed on the surface of the electrode as an oxidation product of Sn2+ ions by the electron tunneling through the space charge layer. The formation of SnO2 layer results in the depression of the oxygen vacancy of the oxide electrode, and the decrease on donor density of the space charge layer. This is also the reason why the photocurrent of the thin film SnO2 electrode is increased remarkably by adding SnSO4 into the electrolyte.