Strategies of metal corrosion protection

The present article involves the electrochemical fundamentals of overvoltage/polarization of charge transfer and preceding diffusion, short-circuited corrosion cells, the mixed potential theory underlying submicrocells, differential de-aeration cells, and finally introduction of two methods, namely potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), of determining corrosion current density i corr and polarization resistance R-p to make strategies to raise the cathodic hydrogen overvoltage/anodic overvoltage with two examples: a sacrificial anode and a green corrosion inhibitor. Carl Wagner's pioneering creative work on the mixed potential theory is addressed with particular emphasis that even nowadays constitutes the principle (classical paradigm) of both the linear polarization and the Tafel extrapolation methods. From the critical assessment of corrosion inhibitors, some unexplained questions are extracted and proposed as formidable future challenges to address in the electrochemistry of corrosion inhibition.