Local analysis of oxygen reduction catalysis by scanning vibrating electrode technique : a new approach to the study of biocorrosion

The scanning vibrating electrode technique (SVET)was employed to investigate oxygen reduction catalysis by the presence of enzyme in an aerobic medium. Heme protoporphyrin (hemin) was chosen as a model of the enzymes that are able to catalyze oxygen reduction. A strict experimental protocol was defined for preparing the graphite surface by deposition of hemin with a simple configuration mimicking the presence of enzyme on the samples. The same configuration was adapted to a stainless steel electrode. Different geometric arrangementswere investigated by SVET to approach the local conditions. The results demonstrated that hemin deposited on the electrode surface led to an increase in the cathodic current, which indicated a catalytic effect. Based on the SVET analysis, itwas demonstrated that hemin caused the appearance of galvanic cells on the material surface. The SVET proved able to locate active catalytic centres and therefore to foresee the contribution of the enzyme to the creation of galvanic cells, thus leading to localized corrosion. The application of SVET to the study of the interaction between biological molecules and material provides a newapproach for visualizing and understanding microbially influenced corrosion (MIC) in an aerobic medium