Sulfur/Nitrogen-Codoped Carbon-Dot-Modified WO₃ Nanosheets toward Enhanced Charge-Carrier Separation in a Saline Water-Splitting Reaction

Hydrogen (H 2 ) is considered to be a future fuel because of its high energy density and could replace fossil fuels. It can be produced in a greener way by using abundant solar light and saline water and applying a photoelectrochemical (PEC) pathway. To produce green H 2, WO 3 2D nanosheets are developed, and their performance in saline water splitting is studied under PEC conditions. WO 3 is very efficient in absorbing visible light from solar irradiation; however, it suffers from low charge-transfer rates, which inhibits its PEC performance. To increase the charge transportation ability, WO 3 is sensitized with sulfur/nitrogen-codoped carbon dots (SNCDs). Impedance analysis indicates an enhanced charge transportation ability of the formed heterostructure. The best-obtained heterostructure of WO 3 and SNCDs exhibits nearly 1.62 times more photocurrent density than bare WO 3 . Bare WO 3 nanosheets can produce a photocurrent density of 1.59 mA/cm 2 at 1.39 V vs Ag/AgCl. The best-obtained heterostructure of WO 3 and SNCDs can produce photocurrent density of 2.57 mA/cm 2 at 1.39 V vs Ag/AgCl. A type II staggered heterostructure of WO 3 /SNCDs leads to improved PEC activity. Enhanced carrier density and lowered charge-transfer resistances are observed from Mott–Schottky and PEC impedance analyses, respectively. The carrier density increases nearly 84 times in the heterostructure. The heterostructure exhibits effective photostability under uninterrupted illumination for 2 h.