In-situ Electron Capture by Surface Co-Ci to Facilitate the Solar Water Splitting of Fe2O3

Surface co-catalyst has been widely used to improve the performance of hematite for solar water splitting. However, the specific working mechanism for co-catalyst has not yet been extensively studied, especially lacking for in-situ information. Here we report a Co-Ci/Zr-Fe2O3 (LV) photoanode for efficient water splitting and probe the working mechanism of surface Co-Ci by in-situ X-ray absorption spectroscopy (XAS) under illumination. The low vacuum treatment and the Zr-doping in Co-Ci/Zr-Fe2O3 (LV) can significantly increase the donor density and then facilitate the bulk charge transfer, while the surface Co-Ci co-catalyst can greatly reduce the electron-hole recombination and then lower the onset potential. In-situ XAS reveals that under illumination, the photonexcited electrons will be quickly transferred to the Co sites in Co-Ci, while the excited holes will be left on Fe to form the high-valence Fe4+ to enhance the oxidation capability. As a result, the combined Co-Ci/Zr-Fe2O3 (LV) photoanode shows a quick bulk charge transfer and a low surface charge recombination, leading to a high photocurrent density of 4.10 mA/cm2 (1.23 VRHE) and a low onset potential of 0.85 VRHE with good stability.