Abstract:

Surface modification of semiconductor materials is an effective way to improve their photocatalysis and photo-conversion activities. Bare and V-modified α-Fe₂O₃ photoelectrode materials were prepared using hydrothermal, chemical bath deposition and heat treatment approaches. Their physicochemical and photoelectrochemical (PEC) properties were then investigated with X-ray diffractometry (XRD), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), voltammetry, and electrochemical AC impedance spectroscopy (EIS) techniques. The existence of FeVO₄ was indicated by its characteristic X-ray diffractometry patterns, while no significant red shifts in the photoabsorption edge were detected in UV-Vis diffuse reflectance spectroscopy spectra. With V-modified and bare Fe₂O₃ serving as a photoanode, photoelectrochemical measurements were carried out for water splitting in 1 molmol·L^-1 NaOH (pH 13.6). The enhancement of α-Fe₂O₃ photoelectrochemical activities through V-modification was indicated by significantly increased photocurrents and decreased photocharge-recombination probability. By measuring electrochemical AC impedance spectroscopy spectra, pseudo-first-order rate constants for the charge transfer at the illuminated electrode/solution interface were estimated. The rate constant for V-modification of the Fe₂O₃ electrode was higher than that of the bare Fe₂O₃ electrode. Improved interfacial charge transfer kinetics through V-modification is responsible for the enhanced photoelectrochemical activities of α-Fe₂O₃. The interfacial photocharge transfer and recombination processes and their properties are discussed with a semiconductor energy band model constructed for the electrode system.

Key words: Water splitting, Interfacial charge transfer, Surface recombination, Photocurrent, AC impedance spectroscopy