Preparation of Co3O4@ZnO core-shell nanocomposites with intrinsic p-n junction as high-performance photoelectrodes for photoelectrochemical cathodic protection under visible light

Abstract In this work, Co3O4@ZnO nanocomposite photoelectrodes with a core-shell structure were prepared, enabling enhanced photoelectrochemical activity under visible light illumination. This was demonstrated by the photoinduced cathodic polarization of 304 stainless steel in 3.5 wt% NaCl solution. The morphology, composition, crystalline structure and optical absorption properties of the photoelectrodes were characterized by various analysis techniques and UV–vis diffuse reflectance absorption spectroscopy. Results show that, compared to the ZnO nanorods, the Co3O4@ZnO nanocomposite photoelectrodes have a red shift of optical absorption and enhanced photoelectrochemical cathodic polarization on stainless steel under visible light. The enhanced photoelectrochemical performance is attributed to the narrow band gap of Co3O4 and the p-n junction formed at the Co3O4/ZnO interface. The Co3O4@ZnO nanocomposite photoelectrodes fabricated in this work achieve a photocurrent density of 10.5 μA/cm2 and a cathodic polarization potential of −720 mV (saturated calomel electrode) for 304 stainless steel in 3.5 wt% NaCl solution under visible light.