Electrochemical impedance spectroscopy of thiourea electro-oxidation on copper electrodes in aqueous 0.5 M sulphuric acid

摘要: The anodisation of copper electrodes in aqueous thiourea (TU) containing 0.5 M sulphuric acid is studied by electrochemical impedance spectroscopy (EIS) combined with rotating disk electrode and ring-disk electrode, SEM EDAX techniques. For E<−0.35 V (vs. MSE), Nyquist plots show two time constants. first one, which appears at high frequencies, involves the contribution double layer capacity charge transfer resistance related to electro-oxidation TU formamidine disulphide (FDS). second constant, observed low complex chemical processes following FDS. Depending on applied potential, this constant can be assigned either an electroadsorption process from products or under diffusion through anodic film. At concentration, frequency corresponds typical response a pure capacitor due formation thick film controlled process. In case, for E≥−0.35 V, exhibit least three constants inductive loop. loop surface relaxation associated pitting. different types films confirmed observations. EIS results are consistent reaction pathway previously proposed TU-containing solutions.