Transforming g-C3N4 from amphoteric to n-type semiconductor: The important role of p/n type on photoelectrochemical cathodic protection

Abstract Photoelectrochemical cathodic protection is emerging as a green and environmental method to protect metals against corrosion. Graphitic carbon nitride (g-C3N4) shows great application potential in this area because of its high efficiency, high stability and low cost. However, the pristine g-C3N4 shows amphoteric properties, resulting in its failure in providing photoelectrochemical cathodic protection for the coupled metal in NaCl solution. In this work, a K&I co-doping technique was performed to modulate the band structure of g-C3N4, and an n-type g-C3N4 (n-C3N4) was obtained. The changes in the molecular structure were studied by SEM, HRTEM, XRD, EDS, XPS and FT-IR technologies. The n-type semiconductor characteristics were verified by the photoinduced i-V curves, SKP potential distributions and pH drift techniques. The n-C3N4 can generate positive photocurrent in the whole investigated potential range, making it able to provide photoelectrochemical cathodic protection for the coupled 316L stainless steel in NaCl solution. This work is very helpful for promoting the application of g-C3N4 in the fields of the photoelectric conversion and the photoelectrochemical cathodic protection.