Photogenerated cathodic protection technology as a valuable branch of photocatalysis and photoelectrochemistry has played a pivotal role in mitigating marine corrosion.

Semiconductor quantum dots with high quantum yield and photovoltaic conversion efficiency have ushered in a brilliant moment for constructing internal electric field heterojunctions for photogenerated cathodic protection applications.

Recently, the research team led by Prof. WANG Jing from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) provided new insight into the elevated photo-induced cathodic protection of CuInS₂/TiO₂ (CIS-9/T) photoanode composites for 304 stainless steel (304 SS) in simulated seawater.

The study was published in Journal of Materials Science & Technology on Mar. 25.

Researchers used immersion, in-situ growth of quantum dots and calcination to sensitise the TiO₂ substrate. They found a possible efficient photo-induced cathodic protection mechanism via photoelectrochemical tests.

Specifically, the oxidated Ti surface was pretreated in L-cysteine (L-cys) solution for couple of days to display sulfhydryl groups for coordinating with heavy metal ions to facilitate the in-situ growth of CuInS₂ quantum dots.

The transient photocurrent of TiO₂ substrates loaded with varying growth times CuInS₂ increased rapidly in the positive direction. Researchers suggested that the deposition of CuInS₂ on TiO₂ will boost the photoelectric conversion efficiency of the composite film and improve the photosensitivity. They pointed out that the most notable increment was observed in CIS-9/T composite, which stabilized at 118 μA·cm^-2, about four times higher than that of pure TiO₂ (29 μA·cm^-2).

Researchers compared six open-circuit potential (OCP) curves, the order of cathodic protection performance of different photoanodes from weak to strong is pure TiO₂, CIS-3/T, CIS-12/T, CIS-18/T, CIS-6/T, and CIS-9/T. Exactly, the CIS-9/T photoanode provided the best photogenerated cathodic protection for 304 SS, with a coupling electrode potential drop of about 0.45 V. They also found numerous heterojunction electric fields were constructed owing to the excellent energy band matching between CuInS₂ and TiO₂. During several irradiation intervals, electrons can migrate uni-directionally to the 304 SS surface to achieve cathodic polarization.

"Heterojunction construction has become the focus of marine anticorrosion. But the application of quantum dots, which have many superior properties, to photo-induced cathodic protection has been relatively little studied. For this study, it is particularly important to use a facile but applicable method to combine carefully selected CuInS₂ semiconductors with TiO₂ to implement synergistic effects," said Prof. WANG.

"At present, in the field of photocathodic protection, many researchers only consider the preparation of excellent performance of photoanode, but ignore how to sensitize the material more firmly anchored on the matrix material, and play a long-term protection. The immersion pretreatment operation in this study provides favorable conditions for the growth of quantum dots later, and thus performs better anticorrosion performance together with TiO₂," said Dr. WANG Ning, first author of the study.

The research was supported by the National Natural Science Foundation of China.

Photocurrent density (A), and the photo-induced cathodic protection mechanism (B), and potential changes (C)

Wang N., Liu, J., Zheng, F.W., Wang C.X., Wang J., Hou, B.R., Zhao, Q.Y., Ning, Y.L., Hu, Y.T. (2022). CuInS₂/TiO₂ heterojunction with elevated photo-electrochemical performance for cathodic protection. Journal of Materials Science & Technology, 122: 211-218.

WANG Jing, WANG Ning

Institute of Oceanology

E-mail: wangjing1@qdio.ac.cn; wangning@qdio.ac.cn 

(Editor: ZHANG Yiyi)