The Preparation And Modification Of ?-Fe₂O₃ Nanorod Photoanodes In Photoelectrochemical Water Splitting System

As a clean,high efficient and renewable energy,hydrogen occupies an important position in energy structure.Photoelectrochemial?PEC?water splitting can utilize water and solar energy to prepare hydrogen,attracting the wide concern of researchers.In this paper,the?-Fe₂O₃ nanorods were prepared and applied as the photoanodes for PEC water splitting.In this work,?-Fe₂O₃ nanorods grown on the fluorine-doped tin oxide?FTO?coated glass substrate with the hydrothermal method and the ethylene glycol?EG?assisted hydrothermal method were annealed under different atmospheres?oxygen,air,nitrogen and argon?and used as the photoanodes.The effect of annealing atmosphere and EG on the surface properties and PEC performance of?-Fe₂O₃ photoanodes were studied by the X-ray diffraction,Scanning electron microscope,X-ray photoelectron spectroscopy,Ultraviolet and visible absorption spectrum,Photocurrent density-voltage curves,Electrochemical impedance spectra and Mott-Schottky technique.The results shows that:i)The lower oxygen concentration in the atmosphere is more conducive to the formation of oxygen vacancy,which can improve the visible light absorption and electron conductivity,reduce the recombination of electron and hole and further enhance the PEC activity of the samples.ii)EG can change the microstructure of the sample and increase specific surface area.Additionally,the carbon of EG was not fully decomposed and stayed in the lattice and surface of?-Fe₂O₃,which helps to increase the electron conductivity and improve the sample PEC activity.iii)The above factors work together making sample AT-EG-Ar which prepared by EG assisted hydrothermal method and annealed in Ar has the best PEC activity with the current density of 0.917 mA·cm^-2?1.23 V vs.RHE?.The value increased by 219.5%than that of AT-EG-O₂(0.287 mA·cm^-2)which prepared by EG assisted hydrothermal method and annealed in O₂,507.3%than that of AT-O₂(0.151 mA·cm^-2)which prepared by hydrothermal method and annealed in O₂ and 15.1%than that of AT-Ar(0.287 mA·cm^-2)which prepared by hydrothermal method and annealed in Ar.The carbon quantum dots?CQDs?and carbon nitride quantum dot?CNQDs?were prepared by electrochemical method and low-temperature solid-phase method,respectively.The hydrothermal method was used to load the quantum dots on the?-Fe₂O₃ nanorods and the effect of CQDs and CNQDs on the PEC performance of?-Fe₂O₃ was investigated.The results showed that:i)CQDs and CNQDs were both beneficial to enhance the visible light absorption and electron conductivity of Fe₂O₃,accelerate the separation and transfer of carriers,and further improve the PEC activity of Fe₂O₃.ii)When CQDs and CNQDs are loaded together,the CNQDs could form heterojunction with Fe₂O₃,and CQDs could accelerate the electron transfer between the heterojunction and also promote the decomposition of H₂O₂ produced on the CNQDs surface,resulting in a further improvement of PEC performance.iii)At a bias of 1.23 V vs.the reversible hydrogen electrode?RHE?,the photocurrent density of samples Fe₂O₃,CQDs/Fe₂O₃,CNQDs/Fe₂O₃ and CQDs@CNQDs/Fe₂O₃ were 0.607,0.722,0.763 and 0.899 mA·cm^-2,respectively.The co-sensitized sample CQDs@CNQDs/Fe₂O₃ has the maximum photocurrent density,achieving an increase of 48.1%in comparison with the blank Fe₂O₃.