Internal polar field is found to be an original and effective method of separate photo generated carriers and thus to enhance the efficiency of photocatalysis. Here, BiOIO3 nanoplate, as a pyroelectric material, is used to probe the influence of internal polar field effect on the separation of photogenerated carriers and photocatalytic H-2 evolution. It is demonstrated that there is a 7-fold increase in the H-2 evolution using 150 nm BiOIO3 nanoplates compared to 25 nm nanoplates in thickness. This achievement is ascribed to the increased internal polar field effect from the increased thickness of the BiOIO3 nano plates. The internal polar field effect ensures a tightly bound layer of the absorbed ions on the surface of BiOIO3 nanoplates, and also acts as an accelerator to separate the photo excited carriers. Both of these features contributed to the enhanced photocatalytic performance of H-2 evolution. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.