Enhanced Charge Transportation in Type II WO 3 /ZnWO 4 Nanoflakes for Boosting Saline Water‐splitting Reaction

Abstract Photoelectrochemical (PEC) water‐splitting is an energy‐efficient and eco‐friendly technique to produce green hydrogen (H 2 ). Here, WO 3 is synthesized for saline water‐splitting reaction. Initially, the activity of WO 3 is enhanced through morphology tuning. Nanoparticles (NPs), thick nanosheets (TSs), and nanoflakes (NFs) of WO 3 are synthesized, and their PEC activity is determined. The NFs show a photocurrent density of 1.53 mA/cm 2 at 1.2 V vs. Ag/AgCl, whereas TSs and NPs can generate 1.17 mA/cm 2 and 1.07 mA/cm 2 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 ZnWO 4 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 WO 3 and 2.4 times enhanced carrier density, 2.16×10 21 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 WO 3 /ZnWO 4 is studied for one hour.