X-ray photoelectron spectroscopy analysis of Mo metal surface exposed to sulfate-reducing bacteria

Molybdenum (Mo) is known for its roles in microbial enzymes and in enhancing the corrosion resistance of engineering alloys. In this study, Mo coupons were exposed to a sulfate-reducing bacterial (SRB) culture Desulfovibrio desulfuricans and then changes in surface chemical states were analyzed by XPS and pitting resistance by potentiodynamic polarization in deaerated 0.1 M HCl. Further investigation was conducted using XPS after potentiostatic polarization of the SRB-exposed Mo coupons at -160 m V_SCE in deaerated 0.1 M HCl. The samples were analyzed with and without the presence of biofilm. Control samples were prepared in uninoculated medium. X-ray photoelectron spectroscopy analysis revealed two effects: the surface stability of Mo coupon was compromised due to MoS₂ formation during exposure to SRB; and molybdate formation induced by bacterial H₂S production was inhibitory to sulfate reduction by forming Mo(V)-S complexes with intermediate sulfur-containing amino groups and proteins. The Mo(V)-S complexes were sparingly soluble and thus protective in the hydrochloric solution.