Synthesis and Photoelectrochemical Properties of Fe2O3/ZnFe2O4 Composite Photoanodes for Use in Solar Water Oxidation

α-Fe2O3/ZnFe2O4 composite electrodes are prepared via a simple surface treatment performed on nanoparticulate α-Fe2O3 electrodes. The α-Fe2O3 electrodes are uniformly covered with a solution containing Zn2+ ions which react with Fe2O3 upon heating to form ZnFe2O4. As Zn2+ ions do not completely diffuse into the core of Fe2O3 particles under mild heating conditions, the ZnFe2O4 forms only on the surface of Fe2O3 as a shell layer, resulting in the formation of Fe2O3/ZnFe2O4 composite electrodes. Any unreacted ZnO is removed by dissolution in 1 M NaOH, where ZnFe2O4 and Fe2O3 are stable. X-ray diffraction and energy-dispersive spectroscopy studies show that a crystalline ZnFe2O4 phase forms after the heat treatment and the composite electrode with the best photoelectrochemical performances contains a 1:1 mol ratio of ZnFe2O4 and Fe2O3. The Fe2O3/ZnFe2O4 composite electrode shows a significantly enhanced photocurrent response compared to the bare Fe2O3 electrode because ZnFe2O4 has conduction and valence band...