Photo-deposition of cobalt-phosphate group modified hematite for efficient water splitting

Abstract

In this work, Cobalt Phosphate Group (Co−Pi) Modified nanostructured hematite (α-Fe2O3) photoanodes films were deposited on fluorine-doped tin oxide (FTO) coated glass by means of the hydrothermal process. The α-Fe2O3 film morphology can be tuned from nanoparticle – based patterns to high-density cabbage-like structures as Co−Pi deposition time is increased.Systematic studies were performed to clarify the mechanisms that enhance water-splitting performance of α-Fe2O3 electrodes as Co−Pi deposition time increases. All samples followed morphological and structural studies using field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. Chronoamperometry measurements showed that Co-Pi/α-Fe2O3 photoanode exhibited higher photoelectrochemical activity than the α-Fe2O3 films. The maximum photocurrent density and incident photon conversion efficiencies (IPCE) were obtained for 30 s Co-Pi/α-Fe2O3 photoanode. All samples reached their best IPCE at 400 nm. IPCE values for 30 s Co-Pi hematite films were 5 times higher than that of α-Fe2O3 sample. For the α-Fe2O3 photoanode, the H2 evolution rate was ∼5.14 μmol cm−2 h−1. After decoration by Co-Pi, the rate increases to ∼7.31 μmol cm−2 h−1, showing an enhancement of about ∼ 42.2%. It was found that under illumination, the Co−Pi catalyst can efficiently collect and store photogenerated holes from the α-Fe2O3 electrode. This charge separation reduces surface state recombination, leading to the enhancement of the efficiency of water oxidation. Thicker catalytic Co−Pi films were found to increase charge separation and surface area, which in turn increase water oxidation efficiency. These results provide important new understanding of the catalytic enhancement and limitations of the Co−Pi catalyst once coupled to semiconductor electrodes for water-splitting applications.