Effect of KOH concentration on corrosion behavior and surface morphology of stainless steel 316L for HHO generator application

Abstract

Hydrogen production could be enhanced by increasing the potassium hydroxide (KOH) concentration, but higher KOH concentrations result in higher corrosion rates. Therefore, a deep investigation of the electrochemical behavior of stainless steel (SS 316L) in the KOH solution is needed. This study investigates the influence of KOH concentrations on the electrochemical behavior, surface morphology, structure, and sample phases of SS 316L. The investigations were conducted by some electrochemical techniques, UV-vis, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD). The corrosion rate was found to increase, and solution resistance to decrease with increasing KOH concentration. Samples tested in 5, 30, and 50 g l-1 of KOH showed corrosion rates of 0.457, 2.362, and 5.613 µm year-1, respectively. A wide passive region and the noblest pitting potential were noticed for the sample with 5 g l-1 of KOH. Moreover, Mott-Schottky plots and characteristic wavelengths of UV-Vis suggest the formation of iron and chromium oxides by the passivation of samples. The SEM analysis showed a dynamic change of surface morphology from the lowest to the highest concentration with the intergranular corrosion found at the grain boundaries area. In conclusion, concentrations < 50 g l-1 KOH could be recommended since they would support the optimum remaining life of SS 316 L plates in HHO generators.