a b s t r a c tThe influence of [Fe-Fe]-hydrogenase from Clostridium acetobutylicum on the anaerobic corrosion of mild steel was studied and the use of a dialysis bag to contain the enzyme in the close vicinity of the electrode surface led to conclusive tests. Electrochemical measurements (open-circuit potential monitoring, corrosion rate evolution, impedance), and surface and medium analysis, all confirmed the strong effect of hydrogenase to exacerbate the corrosion process. Electrolysis performed at a cathodic potential proved that hydrogenase catalysed the electrochemical reduction of protons or water into dihydrogen by direct electron transfer, demonstrating the involvement of hydrogenase in cathodic depolarisation.

a b s t r a c tMild steel coupons were exposed to hydrogenase in a 10 mM phosphate solution. Control coupons were covered by a layer of vivianite. The injection of hydrogenase caused a fast increase in the open circuit potential; this increase depended on the amount of hydrogenase injected and increased from 8 mV for 30 μL hydrogenase to 63 mV for 80 μL. The presence of enzyme resulted in a thicker deposit: high amounts induced the accumulation of corrosion products. Hydrogenase that was deactivated by air revealed a protective effect: non-degradation was observed. In contrast, hydrogenase that was denatured by heat provoked an important deposit of corrosion products with a heterogeneous, cracked structure. The study showed that the action of hydrogenase is not linked to its regular enzymatic activity but to a balance between the protective effect of its protein shell and the electrochemical action of its iron-sulphur clusters. Depending on the operating conditions, hydrogenase can either enhance or mitigate the formation of a corrosion layer on mild steel.