Journal of Oceanology and Limnology https://doi.org/10.1007/s00343-020-9327-y Photoelectrochemical cathodic protection of Cu 2 O/TiO 2 p-n heterojunction under visible light* TIAN Jing 1, 3, 4 , CHEN Zhuoyuan 1, 3, ** , JING Jiangping 1 , FENG Chang 1, 4 , SUN Mengmeng 1 , LI Weibing 2 1 Key Laboratory of Marine Environmental Corrosion and Bio-fouling, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China 2 School of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, China 3 Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China 4 University of Chinese Academy of Sciences, Beijing 100049, China Received Dec. 19, 2019; accepted in principle Jan. 30, 2020; accepted for publication Mar. 16, 2020 © Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract The Cu 2 O/TiO 2 p-n heterojunction composite photoelectrodes were prepared by depositing Cu 2 O nanoparticles on the surface of TiO 2 nanotubes via anodic oxidation and constant current deposition. Field emission scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analyses showed that Cu 2 O nanoparticles not only deposited on the surface of TiO 2 nanotube array, but also on the wall of TiO 2 nanotubes. The Cu 2 O deposition amount could be adjusted by changing the deposition time. The photoelectrochemical cathodic protection (PECCP) performance of the prepared photoelectrodes for 316L stainless steel (SS) was tested under visible light. The constant current deposition time had a significant effect on the PECCP performance of Cu 2 O/TiO 2 -X photoelectrodes and Cu 2 O/TiO 2 -20 had the best PECCP performance for the coupled 316L SS. This was attributed to the appropriate amount and thickness of Cu 2 O to form p-n heterojunctions with TiO 2 , in which separation of the photogenerated carriers was accelerated and transfer of the photogenerated electrons to 316L SS for PECCP was facilitated. Keyword: Cu 2 O/TiO 2 ; p-n heterojunction; 316L SS; photoelectrochemical cathodic protection 1 INTRODUCTION Metallic corrosion can cause huge economic losses and great harm to human’s living environments. Traditional anti-corrosion technologies, such as organic coating and cathodic protection, cause not only waste of resources and energy, but also environmental pollution. The photoelectrochemical cathodic protection (PECCP) technology couples semiconductor materials with metallic materials and transfers the photoinduced electrons generated by the semiconductor materials under light illumination to the metallic materials to protect them. Therefore, the PECCP technology is considered an environmentally friendly novel corrosion protection technology (Bu et al., 2018). Semiconductor materials that can be used for PECCP mainly include TiO 2 (Ohko et al., 2001; Sun et al., 2013; Momeni et al., 2019a), ZnO (Sun et al., 2014; Yang and Cheng, 2018), SrTiO 3 (Yang and Cheng, 2017), and g-C 3 N 4 (Bu et al., 2013; Jing et al., 2019b). Among them, TiO 2 has been widely used in photocatalytic degradation of organic pollutants (Zhuang et al., 2010), dye-sensitized solar cells (Roy et al., 2010; Sauvage et al., 2010), supercapacitors (Lu et al., 2012, 2013), photocatalytic sterilization (Foster et al., 2011; Yadav et al., 2014), photocatalytic hydrogen production (Kho et al., 2010; Xiang et al., 2012), and in other fields since the photoelectric conversion effect was found by Fujishima and Honda (1972). In addition, TiO 2 is of low cost, easy preparation, and good stability, and can control the * Supported by the National Natural Science Foundation of China (Nos. 41576114, 41676069), the State Key Laboratory for Marine Corrosion and Protection, Luoyang Ship Material Research Institute, China (No. 614290101011703), and the Qingdao Innovative Leading Talent Foundation (No. 15-10-3-15-(39)-zch) ** Corresponding author: zychen@qdio.ac.cn