Yb-doped WO3 photocatalysts were prepared by co-sputtering WO3 and Yb, followed by annealing in air for water oxidation with visible light. All the obtained photocatalysts were monoclinic with sputtering power of Yb up to 10 W and displayed no optical absorption red shift. In photoelectrochemical (PEC) studies, the photocurrent densities were improved with up to 0.34 at.% Yb in WO3, with the highest photocurrent of 1.3 mA/cm(2) (1.2 V vs. Ag/AgCl) achieved with <0.1 at.% Yb. Electrochemical impedance spectroscopy (EIS) measurements showed that optimized Yb doping reduced charge transfer resistance and increased donor density of WO3 photocatalyst. The improvement in photocurrent density was attributed to enhanced conductive carrier path, increased oxygen vacancies and 4f(13) orbital configuration due to Yb3+ substitution of W6+. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.