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

Abstract 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 WO3 nanoplate array films, which generated surface oxygen vacancies (Ovs) with the concomitant reduction of surface W6+ to W5+/W4+. As a result, the visible-light absorption and photogenerated charge separation of WO3 was enhanced, as evidenced by X-ray photoelectron spectroscopy (XPS), UV/Vis diffuse-reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. A WO3 photoanode subjected to Ar plasma treatment for 120 s exhibited a photocurrent density of 1.32 mA cm−2 and an O2 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 WO3 photoanode and electrolyte. Our Ar plasma surface modification also has potential for developing other photoanodes for efficient PEC performance.