Electro-oxidation of carbonate in aqueous solution on a platinum rotating ring disk electrode

The kinetics of electro-oxidation of carbonate aqueous solution on a platinum electrode were examined by a rotating ring (platinum) - disk (platinum) electrode in aqueous sodium carbonate/ bicarbonate solutions (25 degrees C, pH = 10.75) with the peroxide stabilizing additives sodium silicate, magnesium sulphate and sodium DTPA such as are used in brightening mechanical wood pulp. A theoretical model based on the experimental data is proposed to describe this electro-oxidation process. The model shows consistency between the experimental results and the expectation from the proposed reaction sequence. The first-order rate constants at 25 degrees C, pH = 10.75 in 1.13 M (Na2CO3 + NaHCO3) for carbonate electro-oxidation to percarbonate ( a. k. a. peroxidicarbonate C2O62-), percarbonate hydrolysis to hydrogen peroxide and hydrogen peroxide electro-oxidation to oxygen are estimated from the experimental data, respectively, as (1.43 +/- 0.1) x 10(-11) cm s(-1) ( extrapolated to the equilibrium electrode potential which is estimated as ca. 0.21 (vs SCE)), (1.1 +/- 0.2) x 10(-2) s(-1) and (5.6 +/- 0.5) x 10(-8) cm s(-1) ( extrapolated to the equilibrium electrode potential of -0.019 V ( vs SCE)).