Physical and photo-electrochemical characterizations of α-Fe2O3. Application for hydrogen production

The optical, electrical and photo-electrochemical properties of dense hematite alpha-Fe2O3 have been studied for the photo-catalytic hydrogen production. The band gap was evaluated at 1.96 eV from the diffuse reflectance spectrum and the transition is directly allowed; further indirect transition occurs at 2.04 eV. The oxygen deficiency permits the altering of the transport properties and the oxide exhibits n type behavior with activation energy of 0.11 eV. alpha-Fe2O3 is found to be photo-electrochemically active. The flat band potential V-fb (-0.51 V-SCE) and the density N-D (19.12 x 10(19) cm(-3)) were obtained respectively by extrapolating the linear part to C-2 = 0 and the slope of the Mott-Schottky plot. The complex impedance pattern is circular in the high frequency region followed by a straight line in the low frequency one, a behavior attributed to the Warburg ionic diffusion. The conduction band edge (-0.62 V-SCE) lies below the H2O/H-2 level (-0.50 V-SCE) and Fe2O3 offers the possibility to be used as hydrogen photocathode. The best activity was obtained in SO32- (0.5 M, pH 13.8) solution with a rate evolution of 6 ml (g catalyst)(-1) min(-1). (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.