Riboflavin as an electron mediator catalyzing the electrochemical reduction of dioxygen with 1,4-naphthoquinones

The electrocatalytic reduction of molecular dioxygen by 1,4-naphthoquinones at a GCE using riboflavin as the electron transfer mediator has been studied. The influence of pH on the electrochemical behaviour of the electrode was studied and pH 7 was chosen as the optimum working pH. Phosphate buffer was found to be a suitable medium to study the electrocatalysis by comparing the shift in the oxygen reduction potential and the enhancement in the peak current for oxygen reduction. 1,4-Naphthoquinones combined with riboflavin possess excellent electrocatalytic abilities for dioxygen reduction with overpotentials ranging from 518 to 755 mV lower than at a plain glassy carbon electrode. The apparent diffusion coefficients of components at the riboflavin modified glassy carbon electrode were determined by chronoamperometric and chronocoulometric techniques. In addition, hydrodynamic voltammetric studies were performed to elucidate the mechanism and to determine the rate constant of oxygen reduction. Studies showed the involvement of two electrons in dioxygen reduction.