Modifying bismuth vanadate (BiVO4) photoanode with secondary component is a promising strategy for improving the performance of photoelectrocatalytic water oxidation. Herein, we investigate on polyoxometalates (POMs) molecular doping in BiVO4 photoanodes to improve photoelectrocatalytic water oxidation performance of BiVO4. The water oxidation performance of BiVO4/POMs photoanodes was markedly enhanced in comparison with pristine BiVO4 photoanode. Moreover, the improved photoelectrocatalytic performance of BiVO4/POMs composite photoanodes is clearly relevant to the type and amount of POMs. The mechanism of the photogenerated electron transfer from BiVO4 to POMs is also revealed by photoluminescence spectroscopy and surface photovoltage measurements. Such a mechanism suggests that the introduction of POMs is capable of facilitating charge separation and transport as well as retarding electron-hole recombination. (C) 2017 Elsevier B.V. All rights reserved.