Sustainable Nickel Recovery and Redeposition from Anodization Electrolyte for Enhanced Hydrogen Evolution on Stainless Steel Electrodes

A sustainable and efficient strategy was developed for fabricating nickel-enriched stainless steel (SS) electrodes with enhanced hydrogen evolution reaction (HER) performance in alkaline media. Anodization of SS in an ethylene glycol-based electrolyte enabled surface roughening and selective dissolution of Ni from low-Ni SS substrate, which was subsequently reused for Ni redeposition onto the anodized SS (ASS) surface. The redeposition parameters, including applied potential and passed charge, were systematically optimized to obtain Ni-ASS electrodes with tailored surface properties. Among them, the Ni-ASS-9 electrode, prepared at −1.1 V vs SCE with 9 C passed charge, exhibited the lowest Tafel slope (98.4 mV dec–1), superior charge transfer kinetics (Rct = 5.09 Ω), and excellent long-term durability. Surface and structural analyses revealed the formation of a Ni-rich, densely packed layer, which significantly increased the electrochemically active surface area. Compared to electrodes fabricated using a conventional NiCl2 aqueous electrolyte, those produced using the reused anodization electrolyte demonstrated finer Ni morphology and superior HER activity, despite lower Ni content. This enhanced performance is attributed to the controlled Ni ion transport and uniform nucleation behavior afforded by the viscous ethylene glycol medium. Furthermore, the reuse of anodization electrolyte offers an environmentally friendly approach by reducing chemical waste and eliminating the need for external Ni sources. This work highlights the dual benefits of sustainable electrolyte recycling and performance optimization for high-efficiency water-splitting electrodes.