A Review on the Application-Focused Assessment of Plasma Electrolytic Oxidation (PEO) Coatings Using Electrochemical Impedance Spectroscopy

The plasma electrolytic oxidation (PEO) coatings have different applications, and their modifications or developments are generally with a specific application target. Therefore, the PEO coating assessments often envisage that particular application without considering other possibilities or infeasibilities of developed PEO coatings from a different perspective. Electrochemical impedance spectroscopy (EIS), a powerful technique for PEO coating assessment, is manifold because it can assess almost every structural, morphological, chemical, and electrochemical feature of PEO coatings. Therefore, a review paper describing an all-purpose EIS behavior of PEO coatings is essential for researchers and engineers for a complete PEO coating assessment beyond their target application. Herein, the relevant PEO coating literature reports sufficient to understand the PEO coating assessment fundamentals are included in this review for researchers and engineers from all perspectives without compiling all literature reports on EIS studies of PEO coatings.