A Z-scheme g-C₃N₄/TiO₂ heterojunction for enhanced performance in protecting magnesium and nickel couple from galvanic corrosion

Large interfacial contact is crucial for designing novel heterostructure materials to achieve good photoelectrochemical performance. Herein, we prepared a composite photoanode consisting of titanium dioxide (TiO₂) nanotubes and graphitic carbon nitride (g-C₃N₄) nanosheets for enhancing the photocathodic protection (PCP) capability of the nickel-coated Mg alloy (Mg/Ni). The composite g-C₃N₄/TiO₂ (CN/TiO₂) photoanode was achieved by depositing g-C₃N₄ on the TiO₂ nanotubes grown titanium foil via a one-step thermal polymerization of melamine and thiourea mixture. A series of characterizations, including transmission electron microscope, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectra, manifested the successful deposition of g-C₃N₄ at the inner wall of the TiO₂ nanotubes to achieve sufficient interfacial contact and the formation of a Z-scheme heterojunction to promote the charge carriers’ transfer and separation. Compared with the pure TiO₂ photoanode, the heterojunction exhibited enhanced photoelectrochemical and photocathodic protection performances, which was confirmed by the electrochemical measurements. The heterojunction achieved a duration of 6.5 h to protect the Mg-Ni couple from galvanic corrosion, representing a tenfold enhancement compared with the uncoupled Mg/Ni electrode. These findings demonstrate the great potential of constructing a unique Z-scheme heterojunction with a sizeable interfacial contact area to enhance the PCP capability of metals.