Facile Solution Synthesis of α-FeF3•3H2O Nanowires and Their Conversion to α-Fe2O3 Nanowires for Photoelectrochemical Application

We report for the first time the facile solution growth of alpha-FeF3 center dot 3H(2)O nanowires (NWs) in large quantity at a low supersaturation level and their scalable conversion to porous semiconducting alpha-Fe2O3 (hematite) NWs of high aspect ratio via a simple thermal treatment in air. The structural characterization by transmission electron microscopy shows that thin alpha-FeF3 center dot 3H(2)O NWs (typically < 100 nm in diameter) are converted to single-crystal alpha-Fe2O3 NWs with internal pores, while thick ones (typically > 100 nm in diameter) become polycrystalline porous alpha-Fe2O3 NWs. We further demonstrated the photoelectrochemical (PEC) application of the nanostructured photoelectrodes prepared from these converted hematite NWs. The optimized photoelectrode with similar to 400 nm thick hematite NW film yielded a photocurrent density of 0.54 mA/cm(2) at 1.23 V vs reversible hydrogen electrode potential after modification with cobalt catalyst under standard conditions (AM 1.5 G, 100 mW/cm(2), pH = 13.6, 1 M NaOH). The low cost, large quantity, and high aspect ratio of the converted hematite NWs, together with the resulting simpler photoelectrode preparation, can be of great benefit for hematite-based PEC water splitting. Furthermore, the ease and scalability of the conversion from hydrated fluoride NWs to oxide NWs suggest a potentially versatile and low-cost strategy to make NWs of other useful iron-based compounds that may enable their large-scale renewable energy applications.