Direct Z-scheme nanoporous BiVO4/CdS quantum dots heterojunction composites as photoanodes for photocathodic protection of 316 stainless steel under visible light

A direct Z-scheme nanoporous BiVO4/CdS quantum dots (QDs) heterojunction composites were successfully synthesized on FTO glass by electrodeposition and successive ionic layer adsorption and reaction (SILAR) methods to improve the photocathodic protection (PCP) ability of BiVO4 under visible light. Results showed that a large number of cubic CdS QDs were uniformly loaded on the nanoporous monoclinic BiVO4 surface. The BiVO4/CdS synthesized by SILAR deposition with 8 cycles showed the optimal PCP performance on the 316 stainless steel (SS) under visible light. The photocurrent density of BiVO4/CdS(8) coupled with 316 SS reached 304 μA·cm−2, which was approximately 5 times that of pure BiVO4. The potential drop of BiVO4/CdS(8) was 330 mV under visible light in 3.5 wt% NaCl solution, which was increased by 154% over pure BiVO4. The improvement of PCP performance of the composites was attributed to the enhanced visible light response and improved photogenerated carrier transport efficiency. The formed direct Z-scheme structure maintained the high redox ability of holes or electrons, thereby improving the PCP performance of BiVO4/CdS. After 10 h of visible light irradiation, the delayed protective effect in the dark state can be maintained for 14 h.