Homophase Junction for Promoting Spatial Charge Separation in Photocatalytic Water Splitting

The widespread heterojunction or p-n junction strategies fabricated between different semiconductors are generally used to promote the spatial charge separation in photocatalysis and solar cells, which originated from the principle that the junction composites possess totally different crystalline and energy structures. A vagarious and supreme challenge remained as to whether a junction could be formed between the identical composites with the same semiconductors and the crystalline phases. Herein, taking model semiconductor TiO2 as a prototype and proof-of-concept, a homophase junction was fabricated between the same crystalline phases of TiO2 with large and small nanoparticles. Photocatalytic H-2 evolution and water splitting performances on three common TiO2, phases, brookite, anatase, and rutile, can be remarkably enhanced using such homophase junction strategy. The high photocatalytic activities are proposed to be attributed to the different surface band bending inducing the formation of a built-in electric field at the interface of large and small particles, which facilitates the spatial charge separation and inhibits the charge recombination. Our work provides a strategy for spatial charge separation in constructing highly efficient solar energy conversion systems, which is differentiated from the traditional junction strategies.