Study of oxygen reduction on copper applied to the peroxidase-mediated oxidation of methylene blue

The kinetics of oxygen reduction was studied on copper in tartarate solutions using a rotating disc electrode. The effect of pH on the cathodic reduction was examined. AC impedance and cathodic polarization curves showed that the reaction is partially controlled by mass transport. At high current densities, the limiting current values showed that O₂ is reduced mainly through the four electron pathway. From measurements of density and viscosity and data taken from Levich and Tafel plots, diffusion coefficients for oxygen in tartarate medium were calculated. Peroxidase-mediated oxidation of methylene blue (MB) results using electrogenerated H₂O₂ on copper electrode showed that O₂ reduction reaction occurs in two steps producing the adsorbed intermediate species H₂O₂ by k ₂. In the absence of peroxidase, the hydrogen peroxide elimination has to be rapid with k ₃ ≫ k _M. The MB oxidation by lignin peroxidase using electrogenerated H₂O₂ was studied. After 24 h LiP is able to oxide the MB, producing different oxidized forms: azure C and thionine, with yield of 23% and 66%, respectively.