Synergistic crystal facet engineering and structural control of WO₃ films exhibiting unprecedented photoelectrochemical performance

WO₃ nanoplate arrays with (002) oriented facets grown on fluorine doped SnO₂ (FTO) glass substrates are tailored by tuning the precursor solution via a facile hydrothermal method. A 2-step hydrothermal method leads to the preferential growth of WO₃ film with enriched (002) facets, which exhibits extraordinary photoelectrochemical (PEC) performance with a remarkable photocurrent density of 3.7 mA cm^-2 at 1.23 V vs. revisable hydrogen electrode (RHE) under AM 1.5 G illumination without the use of any cocatalyst, corresponding to ~93% of the theoretical photocurrent of WO₃. Density functional theory (DFT) calculations together with experimental studies reveal that the enhanced photocatalytic activity and better photo-stability of the WO₃ films are attributed to the synergistic effect of highly reactive (002) facet and nanoplate structure which facilitates the photo-induced charge carrier separation and suppresses the formation of peroxo-species. Without the use of oxygen evolution cocatalysts, the excellent PEC performance, demonstrated in this work, by simply tuning crystal facets and nanostructure of pristine WO₃ films may open up new opportunities in designing high performance photoanodes for PEC water splitting.