Iron Sulfide Formation on Iron Substrates by Electrochemical Reaction in Anoxic Conditions

Electrodeposition has been widely used for the low-cost formation of large-area thin films of various crystalline materials. In this work, we use thermodynamic calculations to guide electrochemical experiments, in which we conduct a systematic investigation of crystalline iron sulfides formation on electrically poised iron substrates in H2S aqueous solutions. Whereas thermodynamic calculations predict the formation of iron pyrite (FeS2) films at the conditions tested, the principal iron-sulfur mineral phases observed were mixtures of mackinawite (Fe1+xS) and cubic iron sulfide (phase identification and characterization included X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy). These data suggest that the phases formed are determined kinetically, not thermodynamically, across all tested electrodeposition conditions. The results are compared with the formation of iron sulfides produced by the "sour corrosion" of iron and steels, and in addition the effects of the experimental variables on the formation and morphologies of crystalline iron sulfides are discussed.