New Progress in Spatial Charge Separation for Photocatalytic Water Splitting
Recently, on the basis of their previous studies towards photogenerated charge separation between different facets of semiconductor-based crystals, Prof. Can Li from SKLC and DNL, rationally designed and controlled the exposed facets of high symmetry SrTiO3 nanocrystal from isotropic facets to anisotropic facets. They found that the reduction and oxidation catalytic sites can only be separately distributed only on the anisotropic facets of 18-facet SrTiO3 nanocrystals. Based on this finding, the selective distribution of dual-cocatalysts on anisotropic facets of 18-facet SrTiO3 nanocrystals leads to a remarkable enhancement of the apparent quantum efficiency. This work has recently been published as an Article in Energy Environ. Sci. (Energy Environ. Sci., 2016, DOI: 10.1039/c6ee00526h).
Hydrogen production by photocatalytic water splitting is regarded as one of the promising solutions to tackle with energy and environmental problems. Charge separation and surface catalytic reactions are of great significance to enhance the efficiency of solar energy conversion. Cocatalysts serve as the active sites and catalyze the proton reduction and water oxidation reactions. Traditionally, cocatalysts are loaded randomly on the surface of photocatalysts by an impregnation or adsorption method. In this case, some cocatalysts are possibly deposited on the wrong sites, e.g., the reduction cocatalyst is deposited on the hole-accumulating site or the oxidation cocatalyst is deposited on the electron-accumulating site, so that the probability for the recombination of charge carriers is increased and the deposited cocatalysts are not fully functioned. It is a big challenge to spatially separate the active sites to efficiently block the charge recombination, especially for some high-symmetric crystals with equivalent exposed facets.
In this work, taking the cubic-phase SrTiO3 crystal as an example, the researchers creatively used a nanocrystal morphology-tailored strategy to rationally controlled the exposed facets of SrTiO3 nanocrystal from isotropic facets (6-facet SrTiO3) to anisotropic facets (18-facet SrTiO3).Interestingly, they found that the reduction and oxidation catalytic sites can only be separately distributed on the anisotropic facets of 18-facet SrTiO3 nanocrystals, but randomly distributed on every facet of 6-facet SrTiO3 nanocrystals. Based on this finding, the selective distribution of dual-cocatalysts on anisotropic facets of 18-facet SrTiO3 nanocrystals leads to a more than fivefold enhancement of the apparent quantum efficiency. The superior performance can be attributed to the charge separation between anisotropic facets and the separation of the reduction and oxidation catalytic sites to reduce the charge recombination. These findings will be instructive for the rational design of constructing a highly efficiency efficient photocatalysttic system for solar energy conversion.
This work has been financially supported by National Natural Science Foundation of China, 973 National Basic Research Program of the Ministry of Science and Technology and the Collaborative Innovation Center of Chemistry for Energy Materials. (Reported by Rengui Li & Linchao Mu).