Here, we demonstrate that ultrathin graphitic-phase C3N4 nanosheets (g-C3N4-NS) could serve as an efficient metal-free cocatalyst for improving oxygen evolution activity on nanoporous BiVO4 photoanode. More specifically, as compared with pure BiVO4 photoanode, ultrathin g-C3N4 nanolayers not only suppress the surface charge recombination of BiVO4, but also effectively transfer and store holes for water oxidation. As expected, the ultrathin graphitic-phase C3N4 cocatalyst modified BiVO4 photoanode exhibited significantly improved photocurrent density and H-2 generation capability, nearly 7 and 12 times with respect to the pristine BiVO4 under the same conditions. These results demonstrate an effective approach for the design and construction of low-cost and highly efficient PEC systems. (C) 2016 Elsevier B.V. All rights reserved.