Lowering the Onset Potential of Fe₂TiO₅/Fe₂O₃ Photoanodes by Interface Structures: F- and Rh-Based Treatments

Hematite is recognized as a promising photocatalyst for solar water oxidation. However, its practical performance at a low bias is still very low due to large onset potential. Here we report a combination of F-treatment and Rh-treatment on Fe₂TiO₅/Fe₂O₃ to lower the onset potential with a large value of 230 mV. The final onset potential is 0.63 V versus RHE comparable to the lowest value ever reported for hematite. The F- and Rh-cotreated photoanode yields a high photocurrent of 1.47 mA/cm² at 1.0 V versus RHE, which is more than 3 times that of the pristine sample. X-ray photoelectron spectroscopy reveals the existence of surface Ti–F bonds after F-treatment. Moreover, the surface groups can be further modified after immersion in the working NaOH solution, which can form an interfacial hydrogen-bond network to accelerate the hole transfer. The surface Fe atoms are also partly reduced to accelerate the hole transport. Rh-treatment can further lower the onset potential with a good stability. The enhanced performance can be attributed to a synergetic effect of F- and Rh-based treatments, in which the F-based interface structure accelerates the hole transfer while the Rh-based material improves the catalytic performance