Enhanced Charge Transportation in Type II WO₃/ZnWO₄ Nanoflakes for Boosting Saline Water‐splitting Reaction

Photoelectrochemical (PEC) water-splitting is an energy-efficient and eco-friendly technique to produce green hydrogen (H₂). Here, WO₃ is synthesized for saline water-splitting reaction. Initially, the activity of WO₃ is enhanced through morphology tuning. Nanoparticles (NPs), thick nanosheets (TSs), and nanoflakes (NFs) of WO₃ are synthesized, and their PEC activity is determined. The NFs show a photocurrent density of 1.53 mA/cm² at 1.2 V vs. Ag/AgCl, whereas TSs and NPs can generate 1.17 mA/cm² and 1.07 mA/cm² at 1.2 V vs. Ag/AgCl, respectively. The low charge transportation rate inhibits the PEC performance of these NFs in water-splitting reactions. To mitigate this problem, the type-II heterojunction is constructed with optimized deposition of ZnWO₄ on WO_3, which favors the migration of charge-carriers in opposite directions, facilitating the charge-carrier separation and eventually enhancing the PEC activity. The optimized heterojunction shows a photocurrent density 1.5 times greater than bare WO₃ and 2.4 times enhanced carrier density, 2.16×10²¹ cm^-3. The heterostructure's rapid OCP decay and higher charge injection efficiency indicate an improved charge transport capability, the primary driving force for enhanced PEC activity. The stability of WO₃/ZnWO₄ is studied for one hour.