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

This work proposes a new strategy to prepare a hematite (α-Fe 2 O 3 ) bilayer photoanode by hydrothermally depositing α-Fe 2 O 3 (B) on the α-Fe 2 O 3 (A) films prepared by electrochemical deposition. Compact smooth surfaced α-Fe 2 O 3 (A) films were electrochemically deposited on FTO (SnO 2 :F) substrates from an aqueous bath. The α-Fe 2 O 3 (A), α-Fe 2 O 3 (B), and α-Fe 2 O 3 /α-Fe 2 O 3 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-Fe 2 O 3 (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-Fe 2 O 3 (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-Fe 2 O 3 (A)/α-Fe 2 O 3 (B) interface. The photoelectrochemical performance of the α-Fe 2 O 3 (A)/α-Fe 2 O 3 (B) structure was examined by chronoamperometry, which found that the α-Fe 2 O 3 (A)/α-Fe 2 O 3 (B) structure exhibited greater photoelectrochemical activity than the α-Fe 2 O 3 (A) and α-Fe 2 O 3 (B) thin films. The highest photocurrent density was obtained for the bilayer α-Fe 2 O 3 (A)/α-Fe 2 O 3 (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-Fe 2 O 3 (A)/α-Fe 2 O 3 (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-Fe 2 O 3 (A)/α-Fe 2 O 3 (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-Fe 2 O 3 (A) and α-Fe 2 O 3 (B) films.