Surface oxygen vacancies on WO3 nanoplate arrays induced by Ar plasma treatment for efficient photoelectrochemical water oxidation

The construction of surface defects on semiconductor oxide photoanodes has been identified as a promising route for attaining improved photoelectrochemical (PEC) performance. Here, Ar plasma treatment has been used to etch the surface of hydrothermally synthesized WO 3 nanoplate array films, which generated surface oxygen vacancies (O v s) with the concomitant reduction of surface W 6+ to W 5+ /W 4+ . As a result, the visible-light absorption and photogenerated charge separation of WO 3 was enhanced, as evidenced by X-ray photoelectron spectroscopy (XPS), UV/Vis diffuse-reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. A WO 3 photoanode subjected to Ar plasma treatment for 120 s exhibited a photocurrent density of 1.32 mA cm −2 and an O 2 evolution rate of 1.0 μmol cm −2 ·min −1 under simulated solar light irradiation at a bias potential of 1.23 V vs. reversible hydrogen electrode, approximately 1.7- and 5-times higher, respectively, than those of a pristine sample. This improvement is mainly attributed to the facilitative effect of surface oxygen vacancy defects, which promote electron–hole generation and separation rates and decrease the interfacial charge-transfer resistance between the WO 3 photoanode and electrolyte. Our Ar plasma surface modification also has potential for developing other photoanodes for efficient PEC performance.