Thermo-selenized stainless steel as an efficient oxygen evolution electrode for water splitting and CO₂ electrolysis in real water matrices

Although stainless steel is a promising candidate for oxygen evolution reaction (OER) electrodes, chalcogenization is typically necessary to avoid surface passivation. Herein, we modify the surface of SUS304 by selenization under mild conditions. The optimal selenization temperature (500 °C) is determined by analyzing the surface morphology and elemental distribution. The electrode composition and the role of Se in improving OER activity are clarified using X-ray photoelectron spectroscopy depth profiling. The electrode selenized at 500 °C is rich in oxygen vacancies and had a high Ni content after electrochemical pre-activation. Moreover, the overpotential is only 284.3 mV at 10 mA cm⁻² and no potential degradation occurred over 160 h, indicating excellent stability under alkaline conditions. Further, high stability is achieved during CO₂ reduction in a real water matrix. These results provide new insights for modifying commercial stainless-steel electrodes to maximize OER activity for alkaline water splitting and neutral CO₂ electrolysis.