Investigation on the CdS-incorporated decorated TiO2 nanoporous arrays as a photoanode for cathodic protection of 304 SS in a 0.5 M NaCl solution

Abstract

A CdS-incorporated TiO₂ nanoporous material was fabricated using an anodic oxidation method combined with a chemical bath deposition technique. The three steps of anodization were completed to grow the anodic TiO₂ nanoporous arrays (TNPs) on a titanium sheet in an ethylene glycol electrolyte containing 0.38wt% NH₄F with the addition of 1.79 wt% H₂O under an applied potential of 40 V. The CdS-decorated TiO₂ nanoporous arrays (CdS/TNPs) were prepared using five dipping cycles of CdS deposition on the TNPs sample, which was calcined at 600°C in air for 3 h at a heating rate of 5 °C min^-1. The structure and composition of the as-prepared TNPs and CdS/TNPs were characterized using field emission scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The photoelectrochemical performance of the TNPs and CdS/TNPs electrode in a 0.5 M NaCl solution was evaluated through the electrochemical measurements under illumination and dark conditions. Decoration of CdS onto the TiO₂ nanoporous array gave a higher transient photocurrent indicating a higher separation efficiency of the photogenerated electron-hole pairs and facile transport of these electrons to the metal substrate. Compared to a bare TiO₂ nanoporous array, the CdS/TNPs photoanode exhibited more effective photocathodic protection properties for 304 stainless steel (304SS) under visible light illumination, with a photopotential of -412 mV versus silver-silver chloride electrode (SSE). This indicates that CdS has an enhanced effect on the photogenerated cathodic protection of TiO₂ nanoporous array for 304SS.