Photoactivities of Nanostructured α-Fe2O3 Anodes Prepared by Pulsed Electrodeposition

Abstract

Ferric oxide (α-Fe2O3, hematite) is an n-type semiconductor; due to its narrow band gap (Eg = 2.1 eV), it is a highly attractive and desirable material for use in solar hydrogenation by water oxidation. However, the actual conversion efficiency achieved with Fe2O3 is considerably lower than the theoretical values because the considerably short diffusion length (2-4 nm) of holes in Fe2O3 induces excessive charge recombination and low absorption. This is a significant hurdle that must be overcome in order to obtain high solar-to-hydrogen conversion efficiency. In consideration of this, it is thought that elemental doping, which may make it possible to enhance the charge transfer at the interface, will have a marked effect in terms of improving the photoactivities of α-Fe2O3 photoanodes. Herein, we report on the synthesis by pulsed electrodeposition of α-Fe2O3-based anodes; we also report on the resulting photoelectrochemical (PEC) properties. We attempted Ti-doping to enhance the PEC properties of α-Fe2O3 anodes. It is revealed that the photocurrent density of a bare α-Fe2O3 anode can be dramatically changed by controlling the condition of the electrodeposition and the concentration of TiCl3. Under optimum conditions, a modified α-Fe2O3 anode exhibits a maximum photocurrent density of 0.4 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) under 1.5 G simulated sunlight illumination; this photocurrent density value is about 3 times greater than that of unmodified α-Fe2O3 anodes. Key words: α-Fe2O3, Pulsed electrodeposition, Water splitting, Doping, TiCl3