A series of heterostructured composites composed of insoluble copper (II) compounds (CuX) loaded on P25, in which the CuX possess different solubility products (K-sp), have been fabricated to compare the charge separation efficiencies and photocatalytic hydrogen production activities. The results indicate that the K-sp of CuX in the as-prepared photocatalysts strongly correlates with the charge separation efficiencies and photocatalytic activities for hydrogen production. The as-optimized Cu-2(OH)(2)CO3/P25 photocatalyst shows an excellent photocatalytic activity for hydrogen production with an apparent quantum efficiency up to 31.9%, far exceeding that of bare P25 by 485 times. An innovative strategy for constructing highly efficient insoluble compound-semiconductor heterostructured photocatalysts is proposed, where regulating the reduction potential (phi) of the insoluble compounds can simultaneously control both the separation efficiency of photogenerated charge carriers and the reduction ability of the transferred electrons. This design strategy shows an obvious advantage that changing K-sp through selecting right Xn- can easily modulate the phi of the insoluble compounds to significantly enhance the photocatalytic activity of the heterostructured photocatalyst. The results reported here not only inspire us to engineer highly efficient photocatalysts by the utilization of insoluble compounds as cocatalysts, but also offer an innovative possibility for the enhanced separation of photogenerated charge carriers in solar cells. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.