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

Hydrogen (H2) 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 H2, WO3 2D nanosheets are developed, and their performance in saline water splitting is studied under PEC conditions. WO3 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, WO3 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 WO3 and SNCDs exhibits nearly 1.62 times more photocurrent density than bare WO3. Bare WO3 nanosheets can produce a photocurrent density of 1.59 mA/cm2 at 1.39 V vs Ag/AgCl. The best-obtained heterostructure of WO3 and SNCDs can produce photocurrent density of 2.57 mA/cm2 at 1.39 V vs Ag/AgCl. A type II staggered heterostructure of WO3/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.