Ultrathin-Layer α-Fe2O3 Deposited under Hematite for Solar Water Splitting

within this work is proposed a new strategy for preparing a Hematite (alpha-Fe2O3) bilayer photoanode, which is prepared by hydrothermally depositing alpha-Fe2O3 (B) on (top of) alpha-Fe2O3 (A) films prepared by electrochemical depositing. Compact and smooth surfaced alpha-Fe2O3 (A) films were deposited electrochemically on a (SnO2: F) FTO substrate from an aqueous bath. The characteristics of the alpha-Fe2O3 (A), alpha-Fe2O3 (B), and alpha-Fe2O3/alpha-Fe2O3 bilayer films were defined by X-Ray Diffraction (XRD) measurements, Field Emission Scanning Electron Microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX). Pure crystalline alpha-Fe2O3 (B) films with typical anisotropic-like nanoparticle formation, that exhibited nanostructured rods covering the Substrate and that formed the characteristic mesoporous film morphology, were hydrothermally deposited on alpha-Fe2O3 (A) films prepared by electrochemical depositing in the solution bath at 25 degrees C and at a potential of -0.15 V. The photocurrent measurements exhibited an increase of the intrinsic surface states (or defects) at the alpha-Fe2O3 (A)/alpha-Fe2O3 (B) interface. The photoelectrochemical performance of the alpha-Fe2O3 (A)/alpha-Fe2O3 (B) structure was examined by chronoamperometry. It was found that the alpha-Fe2O3(A)/alpha-Fe2O3(B) structure exhibits a higher photoelectrochemical activity when compared to alpha-Fe2O3 (A) and alpha-Fe2O3 (B) thin films. The highest photocurrent density was obtained for alpha-Fe2O3 (A)/alpha-Fe2O3 (B) films in 1 M NaOH electrolyte. This high photoactivity was ascribed to the highly active surface area and to the externally applied bias favouring the transfer and separation of photogenerated charge carriers in alpha-Fe2O3 (A)/alpha-Fe2O3 (B). The improvement in the photocurrent density was attributed to an appropriate band edge alignment of the semiconductors as well as enhanced light absorption by both semiconductors. The best performing samples were alpha-Fe2O3 (A)/alpha-Fe2O3 (B) that had (IPCE) Incident Photon Conversion Efficiencies of 400 nm, at the potential of 0.4V vs Ag/AgCl. IPCE values in this case were 3 times higher than the ones of the alpha-Fe2O3 (A) and alpha-Fe2O3 (B) films.