The preparation and electrochemical characterization of glassy carbon electrodes modified with plumbagin were investigated by employing cyclic voltammetry, chronoamperometry and rotating disc electrode techniques. The cyclic voltammograms of the electroreduction of oxygen showed an enhanced current peak at approximately −0.289 V in air-saturated phosphate buffer pH = 7 and scan rate 10 mV s −1 . The thermodynamic and kinetic parameters of the reduction of oxygen at glassy carbon have been evaluated using cyclic voltammetry. The experimental parameters were optimized and the mechanism of the catalytic process was discussed. The obtained values of E′ (V vs. Ag/AgCl), the apparent electron transfer rate constant k s (s −1 ), heterogeneous rate constant for the reduction of O 2 at the surface of the modified electrode k h (M −1 s −1 ) and α (charge transfer coefficient of oxygen) were as follows: −0.146, 23.4, 9.9 10 3 and 0.57, respectively. In addition, plumbagin exhibited strong catalytic activity toward the reduction of H 2 O 2 .
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