title: Photoelectrochemical water splitting with mesoporous hematite prepared by a solution-based colloidal approach.
abstract: Sustainable hydrogen production through photoelectrochemical water splitting using hematite (alpha-Fe(2)O(3)) is a promising approach for the chemical storage of solar energy, but is complicated by the material's nonoptimal optoelectronic properties. Nanostructuring approaches have been shown to increase the performance of hematite, but the ideal nanostructure giving high efficiencies for all absorbed light wavelengths remains elusive. Here, we report for the first time mesoporous hematite photoelectodes prepared by a solution-based colloidal method which yield water-splitting photocurrents of 0.56 mA cm(-2) under standard conditions (AM 1.5G 100 mW cm(-2), 1.23 V vs reversible hydrogen electrode, RHE) and over 1.0 mA cm(-2) before the dark current onset (1.55 V vs RHE). The sintering temperature is found to increase the average particle size, and have a drastic effect on the photoactivity. X-ray photoelectron spectroscopy and magnetic measurements using a SQUID magnetometer link this effect to the diffusion and incorporation of dopant atoms from the transparent conducting substrate. In addition, examining the optical properties of the films reveals a considerable change in the absorption coefficient and onset properties, critical aspects for hematite as a solar energy converter, as a function of the sintering temperature. A detailed investigation into hematite's crystal structure using powder X-ray diffraction with Rietveld refinement to account for these effects correlates an increase in a C(3v)-type crystal lattice distortion to the improved optical properties.
authors.affiliation: Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, Laboratory of Photonics and Interfaces, Station 6, CH-1015 Lausanne, Switzerland. kevin.sivula@epfl.ch
authors.forename: Kevin
authors.initials: K
authors.lastname: Sivula
authors.forename: Radek
authors.initials: R
authors.lastname: Zboril
authors.forename: Florian
authors.initials: F
authors.lastname: Le Formal
authors.forename: Rosa
authors.initials: R
authors.lastname: Robert
authors.forename: Anke
authors.initials: A
authors.lastname: Weidenkaff
authors.forename: Jiri
authors.initials: J
authors.lastname: Tucek
authors.forename: Jiri
authors.initials: J
authors.lastname: Frydrych
authors.forename: Michael
authors.initials: M
authors.lastname: Grätzel