Controllable Band Structure Engineering of CoxNi1−x-ZIF/TiO2 Heterojunction for Durable Photocathodic Protection

Photocathodic protection has emerged as a promising green strategy for mitigating metal corrosion; however, its practical application is still limited by the insufficient visible-light response of conventional semiconductors and the rapid recombination of photogenerated charge carriers. To address these challenges, Co x Ni 1− x -zeolitic imidazolate framework (ZIF)/TiO 2 nanotube array composite photoanodes were fabricated and applied for the photocathodic protection of 304 stainless steel (304SS). By introducing different proportions of Co 2+ and Ni 2+ into the ZIF framework, the electronic structure of the bimetallic ZIFs was effectively regulated. Co 0.5 Ni 0.5 -ZIF exhibited the most favorable band alignment with TiO 2 , enabling the formation of a type-II heterojunction and promoting efficient separation of photogenerated charge carriers. Under illumination in 3.5 wt.% NaCl solution, the optimized composite photoanode induced a negative shift of the open-circuit potential of 304SS to −0.44 V and reduced the corrosion current density by approximately one order of magnitude. Furthermore, pitting corrosion was significantly suppressed, with the pitting potential shifting from −0.50 V to −2.43 V. Long-term immersion tests under natural light conditions demonstrated stable photocathodic protection performance for up to 28 days.