A CuBi₂O₄/TiO₂ p–n Heterojunction for Enhancing the Barrier Protection of a Nickel-Based Layer on the Magnesium Alloy

Herein, CuBi 2 O 4 microspheres were first deposited on TiO 2 nanotube arrays to develop a p–n CuBi 2 O 4 /TiO 2 heterojunction by a facile hydrothermal protocol. The variations in the photoinduced open-circuit potential, photocurrent, and electrochemical parameters of the nickel-plated magnesium alloy (Mg/Ni) demonstrated the remarkably strengthened photoelectrochemical efficiency and photocathodic protection (PCP) capability caused by the CuBi 2 O 4 modification. This enhancement is attributed to establishing a built-in electric field and intensified light absorption in a broadened wavelength spectrum, confirmed by the valence band XPS and ultraviolet–visible spectra. The as-prepared photoanode showed an unprecedentedly high photocurrent density compared with that of current heterojunctions based on CuBi 2 O 4 and TiO 2 semiconductors. The heterojunction continuously provided PCP to the Mg/Ni couple and suppressed the galvanic corrosion between the Mg and nickel–phosphorus alloy. This study proposed a new strategy for constructing a heterojunction with a novel morphology and considerably enhanced photoelectrochemical performance.