Ultrathin-layer α-Fe2O3 deposited under hematite for solar water splitting

This work proposes a new strategy to prepare a hematite (alpha-Fe2O3) bilayer photoanode by hydrothermally depositing alpha-Fe2O3 (B) on the alpha-Fe2O3 (A) films prepared by electrochemical deposition. Compact smooth surfaced alpha-Fe2O3 (A) films were electrochemically deposited on FTO (SnO2:F) substrates from an aqueous bath. The alpha-Fe2O3 (A), alpha-Fe2O3 (B), and alpha-Fe2O3/alpha-Fe2O3 bilayer films' characteristics were defined by X-ray diffraction (XRD) measurements, field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) spectroscopy. Pure crystalline alpha-Fe2O3 (B) films with a typical anisotropic-like nanoparticle formation, which exhibited nanostructured rods covering the substrate and formed the characteristic mesoporous film morphology, were hydrothermally deposited on alpha-Fe2O3 (A) films prepared by electrochemical depositing in a solution bath at 25 A degrees C and a potential of - 0.15 V. The photocurrent measurements exhibited increased 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, which found that the alpha-Fe2O3 (A)/alpha-Fe2O3 (B) structure exhibited greater photoelectrochemical activity than the alpha-Fe2O3 (A) and alpha-Fe2O3 (B) thin films. The highest photocurrent density was obtained for the bilayer alpha-Fe2O3 (A)/alpha-Fe2O3 (B) films in 1 M NaOH electrolyte. This great photoactivity was ascribed to the highly active surface area, and to the externally applied bias that favored the transfer and separation of photogenerated charge carriers in alpha-Fe2O3 (A)/alpha-Fe2O3 (B). The improved photocurrent density was attributed to an appropriate band edge alignment of semiconductors and to enhanced light absorption by both semiconductors. The best performing samples were alpha-Fe2O3 (A)/alpha-Fe2O3 (B), which reached the maximum incident photon conversion efficiencies (IPCE) of 400 nm at the potential of 0.1 V. In this case, the IPCE values were 3-fold higher than those of the alpha-Fe2O3 (A) and alpha-Fe2O3 (B) films.