In₂S₃@TiO₂/In₂S₃ Z-Scheme Heterojunction with Synergistic Effect for Enhanced Photocathodic Protection of Steel

In this work, a TiO₂/In₂S₃ heterojunction film was successfully synthesized using a one-step hydrothermal method and applied in the photocathodic protection (PCP) of 304SS. The octahedral In₂S₃ and In₂S₃@TiO₂ nanoparticles combined and coexisted with each other, with In₂S₃ quantum dots growing on the surface of TiO₂ to form In₂S₃@TiO₂ with a wrapping structure. The composite photoelectrode, which includes TiO₂ with a mixed crystalline phase and In₂S₃, exhibited significantly enhanced PCP performance for 304SS compared with pure In₂S₃ and TiO₂. The In₂S₃@TiO₂/In₂S₃ composites with 0.3 g of P25 titanium dioxide (P25) showed the best protection performance, resulting in a cathodic shift of its OCP coupled with 304SS to -0.664 V_AgCl. The electron transfer tracking results demonstrate that In₂S₃@TiO₂/In₂S₃ forms a Z-scheme heterojunction structure. The enhanced PCP performance could be attributed to the synergistic effect of the mixed crystalline phase and the Z-scheme heterojunction system. The mixed crystalline phase of TiO₂ provides more electrons, and these electrons are gathered at higher energy potentials in the Z-scheme system. Additionally, the built-in electric field further promotes the more effective electrons transfer from photoelectrode to the protected metals, thus, leading to enhanced photoelectrochemical cathodic protection of 304SS.