Effect of HF Treatment on the Photoelectrochemical Properties of a Hematite Thin Film Photoanode for Water Splitting

Abstract

The effects of HF treatment on the photoelectrochemical(PEC) properties of sol-gel prepared hematite(α-Fe2O3) thin films were investigated. Pores and interstices between the grains developed on the film surface as the HF etching time increased. The photocurrent density of the α-Fe2O3photoanode decreased within the first 5 min of etching, and then increased quickly as the etching time increased. At longer time than 15 min the photocurrent density deteriorated. Re-annealing the etched samples significantly enhanced the photocurrent density. Based on electrochemical impedance spectroscopy, Raman and X-ray photoelectron spectroscopies,we propose that two factors contribute to photocurrent density reversely: the porosity and the lowered crystallinity of the α-Fe2O3surface because of HF treatment. A schematic model was compiled to explain the enhanced PEC activities of the etched plus re-annealed α-Fe2O3photoanode. The PEC and water splitting measurements showed that the etched plus re-annealed photoanode is more stable than the as-prepared one.