TiO ₂ /CdZnS/Bi ₂ S ₃ Multiheterojunction Photoanode with Multisynergistic Oxygen Vacancy-Induced Charge Storage Mechanisms for Photoelectrochemical Cathodic Protection

The existing photoelectrochemical cathodic protection (PECCP) technology relies on light-trapped photogenerated electrons for the corrosion protection of metals, but it is difficult to protect them for a long time under dark conditions. To overcome this limitation, a TiO₂/CdZnS/Bi₂S₃ multilayer heterojunction photoanode was constructed. This photoanode achieved highly efficient separation of photogenerated charges and electrons with a photocurrent density of 2.21 mA/cm² by synergistically modulating the energy band gradient, utilizing the energy storage mechanism realized by the oxidative reduction valence change of Bi⁵⁺/Bi³⁺, and engineering the oxygen vacancy (O_V) defect state. Meanwhile, the valence state jump of the photogenerated holes (h⁺) oxidizing Bi³⁺ to Bi⁵⁺ accelerates the depletion of the photogenerated holes in the presence of light. In the dark, Bi⁵⁺ accepts electrons (e^-) to be reduced to Bi³⁺, releasing the stored electrons. Owing to this mechanism, the heterojunction system significantly prolonged the dark protection time to 9.5 h after 1 h of light irradiation. A built-in electric field at the heterojunction interface was realized to drive the directional migration of photoelectrons to the 304 stainless steel substrate (304 SS), providing a new strategy for corrosion protection of metals with full-cycle electronic self-regulation in marine environments.