Ultrathin-layer α-Fe2O3 deposited under hematite for solar water splitting
This work proposes a new strategy to prepare a hematite (α-Fe2O3) bilayer photoanode by hydrothermally depositing α-Fe2O3 (B) on the α-Fe2O3 (A) films prepared by electrochemical deposition. Compact smooth surfaced α-Fe2O3 (A) films were electrochemically deposited on FTO (SnO2:F) substrates from an aqueous bath. The α-Fe2O3 (A), α-Fe2O3 (B), and α-Fe2O3/α-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 α-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 α-Fe2O3 (A) films prepared by electrochemical depositing in a solution bath at 25 °C and a potential of − 0.15 V. The photocurrent measurements exhibited increased intrinsic surface states (or defects) at the α-Fe2O3 (A)/α-Fe2O3 (B) interface. The photoelectrochemical performance of the α-Fe2O3 (A)/α-Fe2O3 (B) structure was examined by chronoamperometry, which found that the α-Fe2O3 (A)/α-Fe2O3 (B) structure exhibited greater photoelectrochemical activity than the α-Fe2O3 (A) and α-Fe2O3 (B) thin films. The highest photocurrent density was obtained for the bilayer α-Fe2O3 (A)/α-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 α-Fe2O3 (A)/α-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 α-Fe2O3 (A)/α-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 α-Fe2O3 (A) and α-Fe2O3 (B) films.
Keywordsα-Fe2O3 Interface Electrochemical deposition Hydrothermal deposition XRD analysis FESEM analysis Optical properties Photoelectrochemical properties
This work was supported by the Ministry of High Education and Scientific Research (Tunisia), Research and Technology Centre of Energy (CRTEn) Borj-Cedria, and the Spanish Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R), and the Generalitat valenciana (Prometeus 2014/044).
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