The mechanism of the chlorine evolution on different types of graphite anodes during the electrolysis of an acidic NaCl solution

The behavior of the electrode and the formation of Cl were studied on porous graphite used in the industrial electrolysis of aq. NaCl. This was done for Acheson graphite electrodes and for highly orientated pyrolytic graphite electrodes of which the edge plane or the basal plane served as electrode surface. Voltammograms were detd. by continuous scanning with different rates of the potential between a min. and max. value. From the exptl. results it follows that 2 different surface compds. the lp O and the hp O are formed on all the graphite electrodes investigated. In the stationary state lp O is present at low potential and the hp O at high potentials. The formation and the removal of each compd. depends on the electrolytic conditions, especially on the max. potential of the sweep. The conditions of the sweep determine whether these oxides are really present on the electrode surface during the anodic or the cathodic sweep. Cl is formed according to the Volmer-Heyrovsky mechanism on all the three types of electrodes. The c.d., the transfer coeff. and the activation energy for the edge plane electrode and the Acheson graphite electrode are of the same order of magnitude, while for the basal plane electrode they deviate strongly. [on SciFinder (R)]