Evaluation of dual layered photoanode for enhancement of visible-light-driven applications

Abstract

Ternary structures consisting of hollow g-C3N4 nanofibers/MoS2/sulfur, nitrogen-doped graphene and bulk g-C3N4 (TCN) were designed as a dual layered film and fabricated using a spin-coating method. The first ternary structures were spin-coated on fluorine-doped tin oxide (FTO) glass, followed by spin-coating of g-C3N4 film to form dual layers. We characterized the microstructural morphologies, chemical composition/bonding and optical properties of the dual layered film and observed significantly reduced recombination rates of photo-induced electron-hole pairs due to effective separation of the charge carriers. We tested methylene blue (MB) photodegradation and observed remarkable MB degradation by the dual layered film over 5 hours, with a kinetic rate constant of 1.24 x 10(-3) min(-1), which is about four times faster than that of bare TCN film. Furthermore, we estimated the H2 evolution of the dual layered film to be 44.9 mmol over 5 hours, and carried out stable recycling over 45 hours under visible irradiation. Due to the lower electrochemical impedance spectroscopy (EIS) resistance value of the dual layered film (similar to 50 ohm cm2) compared to the TCN film, the ternary structures and bulk g-C3N4 film were well-connected as a heterojunction, reducing the resistance at the interface between the film and the electrolyte. These results indicate that the effective separation of the photo-induced electron-hole pairs using the dual layered film dramatically improved its photo-response ability under visible light irradiation.