In situ depositing a metal–organic framework film on TiO₂ nanoarray toward stable photogenerated cathodic protection for nickel-coated magnesium alloy

The photoelectrochemical performance of single TiO₂ nanotubes (NTs) under visible light irradiation is unacceptable for application as a photogenerated cathodic protection photoanode owing to the wide band gap and narrow light absorption range. To develop a stable photoanode for photogenerated cathodic protection, this paper proposes preparing a new class of metal–organic framework (MOF, i.e., UIO-66-NH₂) modified TiO₂ NTs composite by a solvothermal method. An ortho-octahedral structure of the synthesized MOF powder was identified by different characterizations, including high-resolution transmission electron microscopy (HRTEM). X-ray photoelectron spectroscopy (XPS) and HRTEM show that the MOF and TiO₂ form a type-II heterojunction, significantly enhancing the photoelectrochemical performance, confirmed by the electrochemical measurements. Compared with the single-component TiO₂ photoanode, the MOF/TiO₂ composite exhibits significantly higher photogenerated current density by a factor of 3.3, remarkably lower charge transfer resistance, and a negatively shifted bias threshold. The MOF/TiO₂ composite coupled with nickel- phosphorus-plated magnesium alloy (Mg/Ni) is shown to impart the Mg/Ni with more negative and stable polarization potential. This finding indicates that the photoanode can provide stable photogenerated cathodic protection for Mg/Ni electrode. These findings offer insight into preparing highly efficient and durable photocatalytic materials and composite photoanodes for photogenerated cathodic protection.