The study of carrier transfer mechanism for nanostructural hematite photoanode for solar water splitting

Due to the band gap of hematite (α-Fe2O3) (Eg = 2.1 eV) in visible light region, it is regarded as suitable n-type semiconductor material for solar water splitting. Although theoretical conversion efficiency can achieve 12.9%, the drawbacks of hematite, such as short hole diffusion length (∼10 nm), poor charge transport and slow oxygen evolution kinetic rate, cause the generated holes being trapped in photoanodes for low conversion efficiency. In this study, hematite nanorods photoanode was prepared via hydrothermal method and the grain sizes of hematite nanorods increased by adding absolute ethanol into growth aqueous solution. In addition, the morphologies observed by SEM showed that hematite nanorods transformed to nanocorals due to the addition of ethanol. To improve the electrical conductivity for reducing carrier recombination, Ti4+ ions were doped into hematite nanocorals photoanode. Herein, the photocurrent density of Ti-doped hematite nanocorals photoanode could achieve 1.72 mA/cm2 at 1.23 V (vs. RHE). Finally, the surfaces of hematite nanocorals photoanode was decorated by ZnFe2O4 heterojunction layer and Co-Pi oxygen evolution catalysts (OECs) to improve the oxygen evolution reaction. The current density and power conversion efficiency could furthermore improve to 3.60 mA/cm2 at 1.23 V and 0.33%, respectively.