Revealing the Beneficial Effects of FeVO₄ Nanoshell Layer on the BiVO₄ Inverse Opal Core Layer for Photoelectrochemical Water Oxidation

In this paper we developed a template-assisted three-dimensionally ordered BiVO 4 inverse opal (IO) film by sandwich-type infiltration through self-assembled colloidal polystyrene (PS) opal beads with a diameter of 410 nm (±20 nm) for photoelectrochemical hydrogen production. Herein, the ordered BiVO 4 inverse opal structure possessed a pore diameter of ∼340 nm and wall thickness of ∼20 nm, providing a large surface area. Their photoelectrochemical behavior were assessed under 1 sun illumination (100 mW/cm 2 with AM 1.5 filter) in 0.5 M Na 2 SO 4 (pH 7) which displayed a photocurrent density ( J sc ) of 0.8 mA/cm 2 at 1.23 V vs a normal hydrogen electrode (NHE). Low photocurrents of BiVO 4 IO photoelectrodes are due to their limited photoelectrochemical ability to split water under light irradiation and their intrinsically low electronic conductivities. To overcome these problems, BiVO 4 IO film was modified to deposit a nanolayer of n-type FeVO 4 having a narrow band gap ( E g = 2.06 eV). The bilayered BiVO 4 /FeVO 4 core–shell film has efficient photoelectrochemical (PEC) properties compared to unmodified BiVO 4, showing a photocurrent density of 2.5 mA/cm 2 at 1.23 V vs NHE, probably resulting from a favorable charge transfer/transport phenomenon under beneficial band alignment as well as visible light absorption by the FeVO 4 layer.