Facile Surface Treatment of Industrial Stainless Steel Waste Meshes at Mild Conditions to Produce Efficient Oxygen Evolution Catalysts

Herein, the ability to convert waste stainless steel (SS) 316L meshes into highly efficient and durable oxygen evolution reaction (OER) catalysts is demonstrated. The process involves surface treatment of previously anodized SS meshes in different gaseous atmospheres. The activity of the resulted electrocatalysts varies as-anodized SS annealed in oxygen (ASS-O₂) > anodized SS annealed in hydrogen (ASS-H₂) > anodized SS annealed in air (ASS-Air). The ASS-O₂ showed an impressive low overpotential of 280 mV at the benchmark current density of 10 mA/cm², which is 120 mV less than that of the as-received SS (SS-AR), and a low Tafel slope of 63 mV dec^–1 in 1 M KOH. These findings have also been asserted by the estimated electrochemical active surface area, electrochemical impedance spectroscopy analysis, Mott–Schottky analysis, and the calculated turnover frequency, affirming the superiority of the ASS-O₂ electrocatalyst over the ASS-H₂ and ASS-Air counterparts. The high activity of the ASS-O₂ electrocatalyst can be ascribed to the surface composition that is rich in Fe³⁺ and Ni²⁺ as revealed by the X-ray photoelectron spectroscopy analysis. The simple method of anodization and thermal annealing in O₂ at moderate conditions (450 °C for 1 h) lead to the formation of a SS mesh-based OER electrocatalyst with activity exceeding that of the state-of-the-art IrO₂/RuO₂ and other complex modified SS catalysts. These results were also confirmed via density functional theory calculations, which unveiled the OER reaction mechanism and elucidated the d-band center in different SS samples with different oxygen content. The presence of oxygen moved the d-band center closer to the Fermi level in the case of ASS-O₂, explaining its superior activity.