The first part of the work describes experiments performed with a NAD-dependent hydrogenase and a 316L stainless steel electrode in thin spectroelectrochemical cells (TSEC). Constant potential electrolyses were carried out at different potential values. Current and absorbance through the TSEC were recorded simultaneously. The presence of hydrogenase catalyzed the reduction ofNAD + and increased the quantity of electricity consumed. The second part of the study deals with the galvanic coupling of two carbon steel electrodes and hydrogenase in contact of only one of the electrodes. The experiments revealed that the hydrogenase-catalyzed reduction of NAD + spontaneously occurred on carbon steel. Hydrogenase very quickly initiated the corrosion of carbon steel, which was then controlled by other phenomena mainly involving the complexation of iron by phosphates. The cathodic depolarization induced by hydrogenase should be considered more as the catalysis of a reduction reaction, than as the consumption of a reduction product.
It has been widely demonstrated that sulfate-reducing bacteria (SRB) play a major role in the anaerobic microbiologically influenced corrosion (MIC) of carbon steels. ~5 However, the mechanisms proposed to explain anaerobic MIC are still under investigations, l' 6-~4 Von Wolzogen Kuhr and van der Vlugt were first to propose a theory that rests on cathodic depolarization.
