Mechanism of bromine evolution at a graphite electrode

Abstract The mechanism of the electrochemical bromine evolution at a graphite electrode is elucidated. Bromine is formed according to the Volmer-Heyrovsky mechanism, the Heyrovsky reaction being the rate-determining step, For a solution containing 4 M NaBr, 0.1 M Br 2 and 1 M H 2 SO 4 , the activation energy at the reversible potential is 9 ± 2 Kcal/mole; the geometric exchange cd is 0.2 mA/cm 2 at 25°C; the real exchange cds at 25°C of the Volmer and of the Heyrovsky reaction are 2.0 mA/cm 2 and 0.1 mA/cm 2 respectively; the degree of coverage of graphite by atomic bromine at the reversible potential is 0.17; and the transfer coefficient of the Heyrovsky reaction is 0.5.