Two-Step Solvothermal Process for Nanoarchitectonics of Metastable Hexagonal WO₃ Nanoplates

Hexagonal tungsten trioxide (h-WO₃) has shown great potential for application in electrochromic devices, gas sensors, battery electrodes, and as photo-catalysts. The h-WO₃ structure features a unique large network of open hexagonal channels that allow for intercalation. The hydrothermal synthesis of h-WO₃ using sodium tungstate dihydrate as a precursor is widely explored, however, the residual alkaline ions are difficult to eliminate during the synthesis. The solvothermal synthesis using tungsten hexachloride as starting materials largely avoids the use of alkaline ions, but the effect of various synthesis parameters is not well-understood yet. To resolve these ambiguities, this study provides a reliable route to obtain h-WO₃ via solvothermal synthesis and dehydration annealing. The effects of precursor concentration, water content, synthesis temperature, and synthesis time, as well as dehydration temperature, on the as-synthesized crystal structure and crystal morphology are studied.