Effects of In Situ Co or Ni Doping on the Photoelectrochemical Performance of Hematite Nanorod Arrays

Abstract

Co-doped and Ni-doped hematite (α-Fe2O3) nanorod arrays were prepared on fluorine-doped tin oxide (FTO) conductive glass via aqueous chemical growth, in which the doping and the formation of nanorods occurred simultaneously (i.e., in situ doping). These samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet (UV)–visible spectrophotometry, linear sweep voltammetry and Mott–Schottky (M–S) measurement. Results showed that the introduction of 5% Co or Ni into α-Fe2O3 (the molar ratio of dopant to Fe is 1:20) did not change its crystal phase, morphology, energy gap and flat band potential. Both the undoped and the doped α-Fe2O3 showed a direct band gap of 2.24 eV, an indirect band gap of 1.85 eV, and a flat band potential of −0.22 V vs. saturated calomel electrode (SCE). At an applied potential of 0.2 V vs. SCE, the Co-doped and the Ni-doped α-Fe2O3 exhibited a photocurrent of 1.28 mA/cm2 and 0.79 mA/cm2, respectively, which were 2.1 times and 1.3 times that of the undoped α-Fe2O3. After the Co or Ni doping, the charge carrier concentration increased from 1.65 × 1025 m−3 to 3.74 × 1025 m−3 and 2.50 × 1025 m−3, respectively. Therefore, the increase in the photocurrent of the doped α-Fe2O3 was likely attributed to their enhanced conductivity.