Understanding biofilm impact on electrochemical impedance spectroscopy analyses in microbial corrosion and microbial corrosion inhibition phenomena

Electrochemical impedance spectroscopy (EIS) is a non-disruptive technique that can be used to assess the corrosion behavior of materials. In this work, case studies on microbial corrosion (MIC) and microbial corrosion inhibition (MICI), drawn from the recent literature, were re-elaborated and discussed to determine which underlying information EIS analysis could or could not provide, concerning the roles of biofilms and bacteria on the corrosive and inhibitive processes. The data were suitably integrated and elaborated upon using Differential impedance analysis (DIA) to estimate the maximum number of time constants (T) that constituted the electric equivalent circuit (EEC) of each considered corrosion process. Additional analyses on the corrosion products performed by XPS and EIS showed that the bacterial biofilm had a significant influence on the faradaic charge transfer and film resistance of the corrosive process, as well as on its inhibition, at the metal-biofilm interface; however, it did not constitute an additional time constant.