Facile Green Synthesis of WO3·H2O Nanoplates and WO3 Nanowires with Enhanced Photoelectrochemical Performance

The synthesis of nanostructured materials with controlled shape without using a capping agent and/or a hazardous chemical is one of the major existing challenges. Herein, we report a facile precipitation method to synthesize stacked orthorhombic tungsten trioxide hydrate (WO3·H2O) nanoplates by simply mixing WCl6 (0.025 M) in ethanol at room temperature for 1 h. On subsequent solvothermal treatment of WO3·H2O nanoplates at 200 °C in ethanol, formation of monoclinic tungsten trioxide (WO3) nanowires of <20 nm diameter is demonstrated. The morphology evolution of WO3 nanowires from WO3·H2O nanoplates and change in growth direction through dissolution and recrystallization process is further confirmed by varying the solvothermal duration and temperature. The as-synthesized WO3·H2O nanoplates and WO3 nanowires are used as photoanodes for the hydrogen generation through photoelectrochemical (PEC) water splitting in a neutral pH. The photocurrent density of WO3 nanowires is found ∼21 times higher than that of WO3·H2O nanoplates at 1.0 V vs saturated calomel electrode (SCE) and also higher than the reported WO3 nanostructures. The superior PEC performance of WO3 nanowires is justified on the basis of its (200) oriented one-dimensional morphology, large surface area, and small interfacial charge transfer resistance.