Investigation of SOCl₂ Reduction by Cyclic Voltammetry and AC Impedance Measurements

Cyclic voltammetry and ac impedance measurements, covering the range 10⁻³–10⁴ Hz, were employed to investigate the reduction of thionyl chloride on glassy carbon surfaces and to determine the associated elementary processes. The quasi‐exchange current density of the electroreduction of is and becomes larger in the presence of dissolved chlorine. Also, in the presence of , the rest potential shifts to more positive values. At low overpotentials, the reduction of is kinetically controlled. However, as the overpotentials are increased, a transition to mass‐transport control occurs, even before the onset of passivation at +2.7V. The rate of mass transport is governed by the thickness and quality of the film.