High-Efficiency Photocathodic Protection of 304 Stainless Steel by F/N Co-Doped Strontium Titanate Photoanode Materials

Photochemical cathodic protection represents a burgeoning, eco-friendly, and pollution-free technology for metal preservation. Strontium titanate (SrTiO₃), a semiconductor material distinguished by its unique band structure, is particularly well suited for applications in photoelectrochemical cathodic protection. Addressing its limitations through the strategic doping of two nonmetal elements can significantly enhance its photoelectrochemical attributes. In this study, a flower-ball morphology of SrTiO₃ was synthesized via a hydrothermal process. The material was subsequently co-doped with nitrogen and fluorine, sourced from ammonium chloride and sodium fluoride, respectively. This co-doping process was applied to protect 304 stainless steel under a simulated sunlight environment with N/F-x%-SrTiO₃. The outcomes of the experiment demonstrated the successful incorporation of N and F into the SrTiO₃ crystal lattice. The photoanode composed of SrTiO₃ doped with 2% F and 3% N exhibited superior photochemical cathodic protection capabilities. It achieved a photocurrent density of 6.0 μA/cm², and the open-circuit potential shifted negatively to −0.46 V. The co-doping modification with N and F facilitated the formation of impurity energy levels within the bandgap of SrTiO₃. This intervention effectively reduced the semiconductor's bandgap width, thereby increasing the material's sunlight utilization efficiency and bolstering its photochemical cathodic protection performance. This advancement marks a significant stride in the development of SrTiO₃ for applications in metal protection and environmental sustainability.

The application of co-doping techniques significantly enhances the photochemical cathodic protection properties of SrTiO₃. By introducing nitrogen (N) and fluorine (F) into the SrTiO₃ lattice, a novel impurity level is created just above the native valence band. The presence of this impurity level effectively narrows the bandgap of SrTiO₃, leading to an increased absorption of sunlight and a consequent improvement in the utilization of solar energy. Under identical experimental conditions, the photocurrent density of the co-doped SrTiO₃ achieves a remarkable 6 μA/cm², which is a threefold increase compared to that of the undoped SrTiO₃. Furthermore, the open-circuit potential of the doped material exhibits a more negative shift, reaching −0.46 V, a significant improvement of 60 mV over the pure SrTiO₃. These enhancements underscore the effectiveness of the co-doping strategy in optimizing the material's performance for photochemical cathodic protection applications.