Surface decoration of photoanodes with oxygen evolution cocatalysts is an efficient approach to improve the photoelectrochemical water splitting performance. Herein, ultrafine CoOx was selectively immobilized on the surface of BiVO4/WO3 photoanode by using the photogenerated holes to in-situ oxidize Co4O4 cubane. The composited photoanode (CoOx/BiVO4/WO3) displayed an enhanced photoelectrochemical (PEC) water oxidation performance, with a photocurrent density of 2.3 mA/cm(2) at 1.23 V-RHE under the simulated sunlight irradiation, which was 2 times higher than that of bare BiVO4/WO3. The characterization results for the morphological, optical and electrochemical properties of the photoelectrodes revealed that, the enhanced PEC performances could be attributed to the improved charge carrier separation/transport behaviors and the promoted water oxidation kinetics when the photoelectrodes were loaded with CoOx. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.