FeO-Based Hierarchical Structures on FTO Substrates and Their Photocurrent

As one of the most promising photoanode materials for photoelectrochemical (PEC) water oxidation, earth-abundant hematite has been severely restricted by its poor electrical conductivity, poor charge separation, and sluggish oxygen evolution reaction kinetics. FeO has an ability to produce hydrogen, while its preparation needs high temperature to reduce Fe3+ to Fe2+ by using H-2 or CO gases. Here, Fe2O3- and FeO-based nanorods (NRs) on fluorine-doped tin oxide (FTO) substrate have been prepared, where the latter was obtained by doping Sn4+ ions in FeOOH to reduce Fe3+ ions to Fe2+. X-ray diffraction (X-RD) and X-ray photoelectron spectroscopy (XPS) measurements indicate that the dominant content of Fe element on the surface of Sn-doped Fe2O3 and Sn-FeOOH samples is Fe2+. FeO-based NRs have a Fe2O3/FeO heterostructure with some SnO2 nanoparticles distributed on their surface. These prepared samples were used as PEC photoanodes under a visible-light irradiation. The results showed that the modified FeO-based NRs have a photocurrent density of 0.2 mA cm(-2) at 1.23 V vs reference hydrogen electrode (RHE) using Hg/HgO electrode as the reference electrode. Furthermore, they also have a better photocatalytic hydrogen evolution activity with a rate of 2.3 mu mol(-1) h(-1) cm(-1). The improved photocurrent and photocatalytic activity can be ascribed to the Sn-dopant, as the introduction of Sn4+ not only leads to the formation of the Fe2O3/FeO heterostructure but also increases the carrier concentration. Fe2O3/FeO heterostructure with SnO2 nanoparticles on its surface has a good band energy alignment, which is beneficial to the PEC water oxidation and reduction.