Effect of Oxygen–Iron Composition on Charge Transport and Interface Reaction in Hematite

Hematite is composed of iron and oxygen elements, and the iron–oxygen spatial distribution would affect directly its photoelectrochemical (PEC) performance. However, less work has focused on the effect of iron–oxygen composition on the characteristic of charge transport and interfacial reaction. Here, we investigated the charge transfer and interface reaction of two typical iron–oxygen compositions of hematite prepared from the precursors of Fe and FeOOH in which different iron–oxygen ratios were obtained. X-ray photoelectron spectroscopy etching confirms that different precursors do cause differences in spatial elemental composition after thermal treatment. For Fe precursors, oxygen deficiency in the bulk is responsible for its lower bulk efficiency, whereas the defect-free surface results in a high surface separation efficiency and a low interfacial reaction catalysis rate. The FeOOH precursor forms an oxygen-rich surface and, therefore, introduces a large number of surface hole traps. Excessive traps significantly hinder surface charge separation and transport but favor surface electrocatalytic kinetics. Our work provides a perspective on the relationship between the semiconductor electrode performance and its structure and provides effective guidance for further optimization.