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 Fe 3+ to Fe 2+ by using H 2 or CO gases. Here, Fe 2 O 3 - and FeO-based nanorods (NRs) on fluorine-doped tin oxide (FTO) substrate have been prepared, where the latter was obtained by doping Sn 4+ ions in FeOOH to reduce Fe 3+ ions to Fe 2+ . X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements indicate that the dominant content of Fe element on the surface of Sn-doped Fe 2 O 3 and Sn-FeOOH samples is Fe 2+ . FeO-based NRs have a Fe 3 O 2 /FeO heterostructure with some SnO 2 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 μmol h -1 cm -1 . The improved photocurrent and photocatalytic activity can be ascribed to the Sn-dopant, as the introduction of Sn 4+ not only leads to the formation of the Fe 3 O 2 /FeO heterostructure but also increases the carrier concentration. Fe 3 O 2 /FeO heterostructure with SnO 2 nanoparticles on its surface has a good band energy alignment, which is beneficial to the PEC water oxidation and reduction.