Role of H 2O 2 in microbially influenced ennoblement of open circuit potentials for type 316L stainless steel in seawater

Abstract

Type 316L stainless steel specimens were exposed to natural seawater during several seasons. The concentration of H 2O 2 in native biofilms formed on the specimens was detected after the exposures, and open circuit potentials (OCP) for the specimens were also measured. During the summer season, the concentration of H 2O 2 was higher than 10 ppm and OCP were nobler than +0.6 V vs. SHE. On the other hand, during the winter season, the H 2O 2 concentration was lower than 2 ppm and OCP were less noble than +0.3 V vs. SHE. The specimens were exposed to synthetic seawater, to which catalase or peroxidase was added, and H 2O 2 in native biofilms was found to be decomposed. The ennoblement of OCP was offset by the decomposing H 2O 2. The value of OCP for type 316L with H 2O 2-free biofilms was as less noble as that with no biofilm growth.