Surface Engineering of Stainless-Steel 316L and 304L Electrodes for Hydrogen Production in Alkaline and Saline Water

Although green hydrogen is a promising future energy carrier, mass production of green hydrogen via water electrolysis is still contingent upon identifying cost-effective, scalable, and durable electrocatalysts. This study demonstrates a facile, controllable, and scalable process to modify stainless steel’s morphology and chemical composition (SS) via anodic oxidation (anodization). Anodization was performed in an ethylene glycol/H₂SO₄/NH₄F/MeOH-based bath to enhance the surface roughness, while the presence and absence of Cr, Fe, and Ni metal ions in the anodization bath were used to engineer the surface chemical composition. An effective cyclic voltammetry (CV)-based electrochemical activation step was implemented to enhance the electrocatalytic activity of the SS electrodes. The X-ray photoelectron spectroscopy (XPS) analysis confirmed the successful surface oxide reduction and Cr⁶⁺ removal. The anodization bath containing Ni and Fe nitrates resulted in highly rough surfaces with electrochemical active surface areas (ECSA) of 8.4 and 9.8 cm^–2 with a high degree of homogeneity for both SS 316L and SS 304L alloys, respectively. Upon their use as hydrogen evolution catalysts in both alkaline (1 M KOH) and neutral (0.5 M NaCl) aqueous electrolytes, the anodized SS 316L electrode, at the best conditions, exhibited an overpotential of 256 mV at 10 mA/cm² with a decrease in the overpotential and Tafel slope values of 112 and 32 mV/dec, respectively, compared to that of the as-received SS 316L in alkaline water. The hydrogen evolution reaction (HER) was found to follow the Volmer–Heyrovsky mechanism in both alkaline and neutral water, with a difference in the adsorbed hydrogen binding energy, causing a dramatic increase in the overpotential in neutral water compared to the alkaline water.