Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron (III) Oxide

Abstract

AbstractPolycrystalline Mg‐doped (0.1–5 at. %) Fe2O3 photoelectrodes have been prepared by annealing at 1573 K followed by slow cooling in air to ambient temperature. These materials are essentially single‐phase at Mg concentrations not exceeding 0.5 at. %. Disk‐shaped (photo)‐electrodes were prepared, and their electric and photoelectrochemical (PEC) properties were measured. The positive sign of the photovoltage and of the thermoelectric power θ, confirmed the materials to be p‐type semiconducting.—Carrier concentrations calculated from θ, revealed each Mg2+ to introduce one electron‐hole up to about 0.1 at. % Mg. The a.c. conductivities, showing conductivity activation enthalpies of about 0.5 eV in the temperature region 300–800 K, are affected by grain growth and porosity.—The current‐voltage characteristics in the dark and under illumination, the spectral response, and the flatband potential (Vfb = +2.2 V vs. SCE pH = 10) have also been determined.—PEC photocurrents in the visible region correspond to very low (∼0.1%) monochromatic quantum efficiency which is due to the low electron‐hole mobility. The electronic transition in the visible region is indirect, and evidence has been found for this transition to be Fe‐Fe charge transfer. Surface pretreatment is found to have a major effect on the photoelectrochemical properties as deduced from current‐voltage curves. The stability of the α‐Fe2O3 electrode in alkaline solution is discussed.