Graphene-intercalated Fe2O3/TiO2 heterojunctions for efficient photoelectrolysis of water

Interfacial modification of alpha-Fe2O3/TiO2 multilayer photoanodes by intercalating few-layer graphene (FLG) was found to improve water splitting efficiency due to superior transport properties, when compared to individual iron and titanium oxides and heterojunctions thereof. Both metal oxides and graphene sheets were grown by plasma-enhanced chemical vapor deposition. Compared to the onset potential achieved for alpha-Fe2O3 films (1 V vs. RHE), the alpha-Fe2O3/TiO2 bilayer structure yielded a better onset potential (0.3 V vs. RHE). Heterojunctioned bilayers exhibited a higher photocurrent density (0.32 mA cm(-2) at 1.23 V vs. RHE) than the single alpha-Fe2O3 layer (0.22 mA cm(-2) at 1.23 V vs. RHE), indicating more efficient light harvesting and higher concentration of photogenerated charge carriers. For more efficient charge transport at the interface, a few layer graphene sheet was intercalated into the alpha-Fe2O3/TiO2 interface, which substantially increased the photocurrent density to 0.85 mA cm(-2) (1.23 V vs. RHE) and shifted the onset potential (0.25 V vs. RHE). Ultrafast transient absorption spectroscopy studies indicated that the incorporation of FLG between the alpha-Fe2O3 and TiO2 layers resulted in reduced recombination in the alpha-Fe2O3 layer. The results showed that graphene intercalation improved the charge separation and the photocurrent density of the FTO/alpha-Fe2O3/FLG/TiO2 system

Columnar Fe2O3 arrays via plasma-enhanced growth: Interplay of fluorine substitution and photoelectrochemical properties

A single-step plasma enhanced-chemical vapor deposition (PE-CVD) route for the synthesis of F-doped iron(III) oxide nanomaterials is presented. Growth experiments, performed from a fluorinated Fe(II) beta-diketonate precursor on Indium Tin Oxide (ITO) between 200 and 400 degrees C, yielded columnar beta-Fe2O3 arrays with a preferential (100) growth direction. The fluorine content in the deposits could be adjusted by the sole variation of the deposition temperature controlling, in turn, the optical absorption and energy bandgap. Photocurrent measurements and Mott-Schottky analyses, carried out in Na2SO4 solution under one sun illumination, evidenced a conductivity switch from n- to p-type upon increasing fluorine amount in the obtained nanomaterials. The sample photocurrent density, donor content and flatband potential support the hypothesis that a progressive substitution of oxygen by fluorine in the iron(III) oxide lattice can alter electronic structure and extend charge carrier lifetimes, making anion-doped beta-Fe2O3 an efficient water oxidation catalyst. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved