Combined metal ferrite oxide photoanodes and photocathodes for unassisted sunlight-driven tandem photoelectrochemical cells

Abstract

Metal ferrite oxide (MFe2O4) and iron oxide (Fe2O3) were explored as an unassisted operation for the solar light harvesting photoelectrochemical cell (PEC). The metal ferrite oxides studied in this work were CuFe2O4, NiFe2O4, and ZnFe2O4 which were synthesized by the electrochemical deposition method. The crystal structure, surface morphology, and chemical species of the Fe2O3 and metal ferrite oxides were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The result showed that the CuFe2O4 exhibited the p-type semiconductor characteristic while the Fe2O3, NiFe2O4, and ZnFe2O4 exhibited the n-type semiconductor characteristic. Thus, the coupling between the n-type and p-type semiconductors can form the PEC without external bias. As a result, the CuFe2O4 was set as the photocathode while the others were set as the photoanode. The parallel and general tandem photoelectrochemical configurations were investigated. All materials can be used as the unbiased PEC, and the highest performance is the Fe2O3 coupled with the CuFe2O4. The maximum photocurrent of the Fe2O3-CuFe2O4 tandem PEC is ∼6 µA/cm2 in the parallel illumination.