The Study Of The Modification Of α-Fe₂O₃ Photoanode For Photoelectrochemical Water Splitting

Hematite（α-Fe₂O₃）has become a research hotspot due to its suitable optical band gap,non-toxicity and earth-abundance.However,due to the inherent defects of hematite itself,such as poor conductivity,short hole diffusion length and sluggish water oxidation kinetics,it cannot reach the theoretical values of solar to hydrogen conversion efficiency and photocurrent density.Therefore,the modification of hematite is particularly important.The dual modification from the bulk to the surface can greatly alleviate the limitations caused by its inherent defects.We mainly adopt the method of doping in the bulk and depositing the cocatalyst in the surface to modify the hematite,the main contents are as following:1.Construction of efficient hole transfer pathway on the fluorine-doped hematite photoanode for photoelectrochemical water oxidationDual-layers ultrathin（ca.3nm）amorphous Fe OOH and Co OOH cocatalysts were deposited orderly onto F-doped hematite（F-Fe₂O₃）to construct an elaborate photoanode for photoelectrochemical（PEC）water splitting.The co-modification from the bulk to the surface prominently ameliorates the inherent drawbacks ofα-Fe₂O₃photoanode.To be specific,doping with F significantly increases the charge density and improves the electroconductivity of hematite,then amorphous ultrathin Fe OOH layer was deposited to extract photo-induced holes and passivate surface trapping states for accelerated charge transfer.Whereafter,through photo-assisted electrodeposition,Co OOH as an excellent cocatalyst was coated onto Fe OOH/F-Fe₂O₃ remarkably expediting oxygen evolution reaction（OER）kinetics.This co-modification treatment satisfies the needs of both high charge transfer/separation efficiency and beneficial kinetics,displaying a satisfactory photocurrent density（3.3-fold higher than bareα-Fe₂O₃）and negative shifted onset potential of 80 m V versus RHE.The bulk charge separation efficiency and the surface hole injection efficiency are significantly improved compared withα-Fe₂O₃,and the incident photon-to-current conversion efficiency（IPCE）reaches 49%.2.Doping in the bulk and the surface to ameliorate the hematite anode for photoelectrochemical water oxidationAiming at the drawbacks of hematite like poor conductivity and tardy oxidation kinetics,herein,we utilized dual dopants in the bulk and surface to ameliorate the situation.Specifically,doping optimal amount of Zr in the hematite（Zr:Fe₂O₃）not only changes the morphology but also enhances the conductivity of the hematite,resulting a higher charge carriers density and charge separation efficiency.Based on this,further doping with F in the Fe OOH,the OER kinetics are accelerated,because of an enhanced activate sites compared with single Fe OOH cocatalyst.the composite anode（F:Fe OOH/Zr:Fe₂O₃）shows a negatively shifted onset potential of 120 m V relative to Zr:Fe₂O₃,and a 3.25 times enhanced of photocurrent density comparing withα-Fe₂O₃,which is put down to the formation of p-n juntion between F:Fe OOH and Zr:Fe₂O₃.The charge separation efficiency of the bulk and surface reached 14.6%and 84.0%,respectively,which were significantly improved compared withα-Fe₂O₃（7.7%,46.6%）.