A stable S-scheme heterojunction for sustainable photoelectrochemical cathodic protection of nickel-phosphorus-coated magnesium alloy

A novel and long-lasting N 3 BD/TiO 2 composite photoanode with stable and superior photoelectrochemical and photoelectrochemical cathodic protection (PECCP) performances was achieved by synthesizing and depositing covalent organic framework (N 3 BD) on titanium oxide (TiO 2 ) nanotube arrays. The composite's increased visible light absorption capability enhanced the galvanic corrosion protection of nickel-phosphorus alloy-coated magnesium alloy (Mg/Ni) through PECCP technology. The open circuit potential (OCP) drops of the Mg/Ni electrode coupling with the N 3 BD/TiO 2 composite were 310 and 630 mV at dark state and under illumination, respectively. They remained relatively stable under intermittent visible light irradiation within 72 h, demonstrating excellent long-term stability. The superior photoelectrochemical and PECCP properties of the N 3 BD/TiO 2 are attributed to forming S-scheme heterojunctions, which effectively promote the separation and transfer of photogenerated electron-hole pairs and retain a strong redox capacity. This finding provides new insight into the design and synthesis of COF-modified photoanode with highly efficient and stable photoelectrochemical and PECCP performances.