Photocatalytic Hydrogen Evolution from Substoichiometric Colloidal WO_3–x Nanowires

We report direct photocatalytic hydrogen evolution from substoichiometric highly reduced tungsten oxide (WOx) nanowires (NWs) using sacrificial alcohol. WOx NWs are synthesized via nonaqueous colloidal synthesis with a diameter of about 4 nm and an average length of about 250 nm. As-synthesized WOx NWs exhibit a broad absorption across the visible to infrared regions attributed to the presence of oxygen vacancies. The optical band gap is increased in these WOx NWs compared to stoichiometric bulk tungsten oxide (WO3) powders as a result of the Burstein–Moss shift. As a consequence of this increase, we demonstrate direct photocatalytic hydrogen production from WOx NWs through alcohol photoreforming. The stable H2 evolution on platinized WOx NWs is observed under conditions in which platinized bulk WO3 and bulk WO2.9 powders either do not show activity or show very low rates, suggesting that increased surface area and specific exposed facets are key for the improved performance of WOx NWs. This work demonstrates that control of size and composition can lead to unexpected and beneficial changes in the photocatalytic properties of semiconductor materials.